Auto merge of #52336 - ishitatsuyuki:dyn-rollup, r=Mark-Simulacrum

Rollup of bare_trait_objects PRs

All deny attributes were moved into bootstrap so they can be disabled with a line of config.

Warnings for external tools are allowed and it's up to the tool's maintainer to keep it warnings free.

r? @Mark-Simulacrum
cc @ljedrz @kennytm

112 files changed, 315 insertions, 345 deletions

diff --git a/src/bootstrap/bin/rustc.rs b/src/bootstrap/bin/rustc.rs
index f2b2f6f1eeb..7192cae8956 100644
--- a/src/bootstrap/bin/rustc.rs
+++ b/src/bootstrap/bin/rustc.rs
@@ -296,8 +296,10 @@ fn main() {
         cmd.arg("--color=always");
     }
 
-    if env::var_os("RUSTC_DENY_WARNINGS").is_some() {
+    if env::var_os("RUSTC_DENY_WARNINGS").is_some() && env::var_os("RUSTC_EXTERNAL_TOOL").is_none()
+    {
         cmd.arg("-Dwarnings");
+        cmd.arg("-Dbare_trait_objects");
     }
 
     if verbose > 1 {
diff --git a/src/bootstrap/check.rs b/src/bootstrap/check.rs
index 39c5c832831..8838cdeed86 100644
--- a/src/bootstrap/check.rs
+++ b/src/bootstrap/check.rs
@@ -12,7 +12,7 @@
 
 use compile::{run_cargo, std_cargo, test_cargo, rustc_cargo, rustc_cargo_env, add_to_sysroot};
 use builder::{RunConfig, Builder, ShouldRun, Step};
-use tool::{self, prepare_tool_cargo};
+use tool::{self, prepare_tool_cargo, SourceType};
 use {Compiler, Mode};
 use cache::{INTERNER, Interned};
 use std::path::PathBuf;
@@ -222,7 +222,8 @@ impl Step for Rustdoc {
                                            Mode::ToolRustc,
                                            target,
                                            "check",
-                                           "src/tools/rustdoc");
+                                           "src/tools/rustdoc",
+                                           SourceType::InTree);
 
         let _folder = builder.fold_output(|| format!("stage{}-rustdoc", compiler.stage));
         println!("Checking rustdoc artifacts ({} -> {})", &compiler.host, target);
diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index f71cb119b77..fd3730ffc78 100644
--- a/src/bootstrap/doc.rs
+++ b/src/bootstrap/doc.rs
@@ -28,7 +28,7 @@ use build_helper::up_to_date;
 
 use util::symlink_dir;
 use builder::{Builder, Compiler, RunConfig, ShouldRun, Step};
-use tool::{self, prepare_tool_cargo, Tool};
+use tool::{self, prepare_tool_cargo, Tool, SourceType};
 use compile;
 use cache::{INTERNER, Interned};
 use config::Config;
@@ -814,6 +814,7 @@ impl Step for Rustdoc {
             target,
             "doc",
             "src/tools/rustdoc",
+            SourceType::InTree,
         );
 
         cargo.env("RUSTDOCFLAGS", "--document-private-items");
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 639c96bc208..7c69197885c 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -30,7 +30,7 @@ use compile;
 use dist;
 use flags::Subcommand;
 use native;
-use tool::{self, Tool};
+use tool::{self, Tool, SourceType};
 use toolstate::ToolState;
 use util::{self, dylib_path, dylib_path_var};
 use Crate as CargoCrate;
@@ -222,17 +222,18 @@ impl Step for Cargo {
             compiler,
             target: self.host,
         });
-        let mut cargo = builder.cargo(compiler, Mode::ToolRustc, self.host, "test");
-        cargo
-            .arg("--manifest-path")
-            .arg(builder.src.join("src/tools/cargo/Cargo.toml"));
+        let mut cargo = tool::prepare_tool_cargo(builder,
+                                                 compiler,
+                                                 Mode::ToolRustc,
+                                                 self.host,
+                                                 "test",
+                                                 "src/tools/cargo",
+                                                 SourceType::Submodule);
+
         if !builder.fail_fast {
             cargo.arg("--no-fail-fast");
         }
 
-        // Don't build tests dynamically, just a pain to work with
-        cargo.env("RUSTC_NO_PREFER_DYNAMIC", "1");
-
         // Don't run cross-compile tests, we may not have cross-compiled libstd libs
         // available.
         cargo.env("CFG_DISABLE_CROSS_TESTS", "1");
@@ -286,10 +287,8 @@ impl Step for Rls {
                                                  Mode::ToolRustc,
                                                  host,
                                                  "test",
-                                                 "src/tools/rls");
-
-        // Don't build tests dynamically, just a pain to work with
-        cargo.env("RUSTC_NO_PREFER_DYNAMIC", "1");
+                                                 "src/tools/rls",
+                                                 SourceType::Submodule);
 
         builder.add_rustc_lib_path(compiler, &mut cargo);
 
@@ -341,10 +340,9 @@ impl Step for Rustfmt {
                                                  Mode::ToolRustc,
                                                  host,
                                                  "test",
-                                                 "src/tools/rustfmt");
+                                                 "src/tools/rustfmt",
+                                                 SourceType::Submodule);
 
-        // Don't build tests dynamically, just a pain to work with
-        cargo.env("RUSTC_NO_PREFER_DYNAMIC", "1");
         let dir = testdir(builder, compiler.host);
         t!(fs::create_dir_all(&dir));
         cargo.env("RUSTFMT_TEST_DIR", dir);
@@ -392,13 +390,14 @@ impl Step for Miri {
             extra_features: Vec::new(),
         });
         if let Some(miri) = miri {
-            let mut cargo = builder.cargo(compiler, Mode::ToolRustc, host, "test");
-            cargo
-                .arg("--manifest-path")
-                .arg(builder.src.join("src/tools/miri/Cargo.toml"));
+            let mut cargo = tool::prepare_tool_cargo(builder,
+                                                 compiler,
+                                                 Mode::ToolRustc,
+                                                 host,
+                                                 "test",
+                                                 "src/tools/miri",
+                                                 SourceType::Submodule);
 
-            // Don't build tests dynamically, just a pain to work with
-            cargo.env("RUSTC_NO_PREFER_DYNAMIC", "1");
             // miri tests need to know about the stage sysroot
             cargo.env("MIRI_SYSROOT", builder.sysroot(compiler));
             cargo.env("RUSTC_TEST_SUITE", builder.rustc(compiler));
@@ -450,13 +449,14 @@ impl Step for Clippy {
             extra_features: Vec::new(),
         });
         if let Some(clippy) = clippy {
-            let mut cargo = builder.cargo(compiler, Mode::ToolRustc, host, "test");
-            cargo
-                .arg("--manifest-path")
-                .arg(builder.src.join("src/tools/clippy/Cargo.toml"));
+            let mut cargo = tool::prepare_tool_cargo(builder,
+                                                 compiler,
+                                                 Mode::ToolRustc,
+                                                 host,
+                                                 "test",
+                                                 "src/tools/clippy",
+                                                 SourceType::Submodule);
 
-            // Don't build tests dynamically, just a pain to work with
-            cargo.env("RUSTC_NO_PREFER_DYNAMIC", "1");
             // clippy tests need to know about the stage sysroot
             cargo.env("SYSROOT", builder.sysroot(compiler));
             cargo.env("RUSTC_TEST_SUITE", builder.rustc(compiler));
@@ -1739,7 +1739,8 @@ impl Step for CrateRustdoc {
                                                  Mode::ToolRustc,
                                                  target,
                                                  test_kind.subcommand(),
-                                                 "src/tools/rustdoc");
+                                                 "src/tools/rustdoc",
+                                                 SourceType::InTree);
         if test_kind.subcommand() == "test" && !builder.fail_fast {
             cargo.arg("--no-fail-fast");
         }
diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 0969e5abe07..5e68b797b3d 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -76,13 +76,20 @@ impl Step for CleanTools {
 }
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
+pub enum SourceType {
+    InTree,
+    Submodule,
+}
+
+#[derive(Debug, Clone, Hash, PartialEq, Eq)]
 struct ToolBuild {
     compiler: Compiler,
     target: Interned<String>,
     tool: &'static str,
     path: &'static str,
     mode: Mode,
-    is_ext_tool: bool,
+    is_optional_tool: bool,
+    source_type: SourceType,
     extra_features: Vec<String>,
 }
 
@@ -102,7 +109,7 @@ impl Step for ToolBuild {
         let target = self.target;
         let tool = self.tool;
         let path = self.path;
-        let is_ext_tool = self.is_ext_tool;
+        let is_optional_tool = self.is_optional_tool;
 
         match self.mode {
             Mode::ToolRustc => {
@@ -115,7 +122,15 @@ impl Step for ToolBuild {
             _ => panic!("unexpected Mode for tool build")
         }
 
-        let mut cargo = prepare_tool_cargo(builder, compiler, self.mode, target, "build", path);
+        let mut cargo = prepare_tool_cargo(
+            builder,
+            compiler,
+            self.mode,
+            target,
+            "build",
+            path,
+            self.source_type,
+        );
         cargo.arg("--features").arg(self.extra_features.join(" "));
 
         let _folder = builder.fold_output(|| format!("stage{}-{}", compiler.stage, tool));
@@ -216,7 +231,7 @@ impl Step for ToolBuild {
         });
 
         if !is_expected {
-            if !is_ext_tool {
+            if !is_optional_tool {
                 exit(1);
             } else {
                 return None;
@@ -238,6 +253,7 @@ pub fn prepare_tool_cargo(
     target: Interned<String>,
     command: &'static str,
     path: &'static str,
+    source_type: SourceType,
 ) -> Command {
     let mut cargo = builder.cargo(compiler, mode, target, command);
     let dir = builder.src.join(path);
@@ -247,6 +263,10 @@ pub fn prepare_tool_cargo(
     // stages and such and it's just easier if they're not dynamically linked.
     cargo.env("RUSTC_NO_PREFER_DYNAMIC", "1");
 
+    if source_type == SourceType::Submodule {
+        cargo.env("RUSTC_EXTERNAL_TOOL", "1");
+    }
+
     if let Some(dir) = builder.openssl_install_dir(target) {
         cargo.env("OPENSSL_STATIC", "1");
         cargo.env("OPENSSL_DIR", dir);
@@ -274,7 +294,8 @@ pub fn prepare_tool_cargo(
 }
 
 macro_rules! tool {
-    ($($name:ident, $path:expr, $tool_name:expr, $mode:expr $(,llvm_tools = $llvm:expr)*;)+) => {
+    ($($name:ident, $path:expr, $tool_name:expr, $mode:expr
+        $(,llvm_tools = $llvm:expr)* $(,is_external_tool = $external:expr)*;)+) => {
         #[derive(Copy, PartialEq, Eq, Clone)]
         pub enum Tool {
             $(
@@ -351,7 +372,12 @@ macro_rules! tool {
                     tool: $tool_name,
                     mode: $mode,
                     path: $path,
-                    is_ext_tool: false,
+                    is_optional_tool: false,
+                    source_type: if false $(|| $external)* {
+                        SourceType::Submodule
+                    } else {
+                        SourceType::InTree
+                    },
                     extra_features: Vec::new(),
                 }).expect("expected to build -- essential tool")
             }
@@ -370,7 +396,8 @@ tool!(
     Compiletest, "src/tools/compiletest", "compiletest", Mode::ToolBootstrap, llvm_tools = true;
     BuildManifest, "src/tools/build-manifest", "build-manifest", Mode::ToolBootstrap;
     RemoteTestClient, "src/tools/remote-test-client", "remote-test-client", Mode::ToolBootstrap;
-    RustInstaller, "src/tools/rust-installer", "fabricate", Mode::ToolBootstrap;
+    RustInstaller, "src/tools/rust-installer", "fabricate", Mode::ToolBootstrap,
+        is_external_tool = true;
     RustdocTheme, "src/tools/rustdoc-themes", "rustdoc-themes", Mode::ToolBootstrap;
 );
 
@@ -401,7 +428,8 @@ impl Step for RemoteTestServer {
             tool: "remote-test-server",
             mode: Mode::ToolStd,
             path: "src/tools/remote-test-server",
-            is_ext_tool: false,
+            is_optional_tool: false,
+            source_type: SourceType::InTree,
             extra_features: Vec::new(),
         }).expect("expected to build -- essential tool")
     }
@@ -449,12 +477,15 @@ impl Step for Rustdoc {
             target: builder.config.build,
         });
 
-        let mut cargo = prepare_tool_cargo(builder,
-                                           build_compiler,
-                                           Mode::ToolRustc,
-                                           target,
-                                           "build",
-                                           "src/tools/rustdoc");
+        let mut cargo = prepare_tool_cargo(
+            builder,
+            build_compiler,
+            Mode::ToolRustc,
+            target,
+            "build",
+            "src/tools/rustdoc",
+            SourceType::InTree,
+        );
 
         // Most tools don't get debuginfo, but rustdoc should.
         cargo.env("RUSTC_DEBUGINFO", builder.config.rust_debuginfo.to_string())
@@ -525,7 +556,8 @@ impl Step for Cargo {
             tool: "cargo",
             mode: Mode::ToolRustc,
             path: "src/tools/cargo",
-            is_ext_tool: false,
+            is_optional_tool: false,
+            source_type: SourceType::Submodule,
             extra_features: Vec::new(),
         }).expect("expected to build -- essential tool")
     }
@@ -574,7 +606,8 @@ macro_rules! tool_extended {
                     mode: Mode::ToolRustc,
                     path: $path,
                     extra_features: $sel.extra_features,
-                    is_ext_tool: true,
+                    is_optional_tool: true,
+                    source_type: SourceType::Submodule,
                 })
             }
         }
diff --git a/src/build_helper/lib.rs b/src/build_helper/lib.rs
index 00e5dee256e..1cbb8e49bfa 100644
--- a/src/build_helper/lib.rs
+++ b/src/build_helper/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 use std::fs::File;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 63cf01a0fac..ef619527e06 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -72,7 +72,6 @@
        test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 #![no_std]
 #![needs_allocator]
-#![deny(bare_trait_objects)]
 #![deny(missing_debug_implementations)]
 
 #![cfg_attr(test, allow(deprecated))] // rand
diff --git a/src/liballoc/tests/arc.rs b/src/liballoc/tests/arc.rs
index 753873dd294..d90c22a3b18 100644
--- a/src/liballoc/tests/arc.rs
+++ b/src/liballoc/tests/arc.rs
@@ -18,7 +18,7 @@ fn uninhabited() {
     a = a.clone();
     assert!(a.upgrade().is_none());
 
-    let mut a: Weak<Any> = a;  // Unsizing
+    let mut a: Weak<dyn Any> = a;  // Unsizing
     a = a.clone();
     assert!(a.upgrade().is_none());
 }
@@ -39,7 +39,7 @@ fn slice() {
 #[test]
 fn trait_object() {
     let a: Arc<u32> = Arc::new(4);
-    let a: Arc<Any> = a;  // Unsizing
+    let a: Arc<dyn Any> = a;  // Unsizing
 
     // Exercise is_dangling() with a DST
     let mut a = Arc::downgrade(&a);
@@ -49,7 +49,7 @@ fn trait_object() {
     let mut b = Weak::<u32>::new();
     b = b.clone();
     assert!(b.upgrade().is_none());
-    let mut b: Weak<Any> = b;  // Unsizing
+    let mut b: Weak<dyn Any> = b;  // Unsizing
     b = b.clone();
     assert!(b.upgrade().is_none());
 }
diff --git a/src/liballoc/tests/btree/set.rs b/src/liballoc/tests/btree/set.rs
index 6171b8ba624..0330bda5e32 100644
--- a/src/liballoc/tests/btree/set.rs
+++ b/src/liballoc/tests/btree/set.rs
@@ -40,7 +40,7 @@ fn test_hash() {
 }
 
 fn check<F>(a: &[i32], b: &[i32], expected: &[i32], f: F)
-    where F: FnOnce(&BTreeSet<i32>, &BTreeSet<i32>, &mut FnMut(&i32) -> bool) -> bool
+    where F: FnOnce(&BTreeSet<i32>, &BTreeSet<i32>, &mut dyn FnMut(&i32) -> bool) -> bool
 {
     let mut set_a = BTreeSet::new();
     let mut set_b = BTreeSet::new();
diff --git a/src/liballoc/tests/lib.rs b/src/liballoc/tests/lib.rs
index 2c361598e89..91bc778ad4c 100644
--- a/src/liballoc/tests/lib.rs
+++ b/src/liballoc/tests/lib.rs
@@ -63,7 +63,7 @@ fn test_boxed_hasher() {
     5u32.hash(&mut hasher_1);
     assert_eq!(ordinary_hash, hasher_1.finish());
 
-    let mut hasher_2 = Box::new(DefaultHasher::new()) as Box<Hasher>;
+    let mut hasher_2 = Box::new(DefaultHasher::new()) as Box<dyn Hasher>;
     5u32.hash(&mut hasher_2);
     assert_eq!(ordinary_hash, hasher_2.finish());
 }
diff --git a/src/liballoc/tests/rc.rs b/src/liballoc/tests/rc.rs
index baa0406acfc..9ec7c831444 100644
--- a/src/liballoc/tests/rc.rs
+++ b/src/liballoc/tests/rc.rs
@@ -18,7 +18,7 @@ fn uninhabited() {
     a = a.clone();
     assert!(a.upgrade().is_none());
 
-    let mut a: Weak<Any> = a;  // Unsizing
+    let mut a: Weak<dyn Any> = a;  // Unsizing
     a = a.clone();
     assert!(a.upgrade().is_none());
 }
@@ -39,7 +39,7 @@ fn slice() {
 #[test]
 fn trait_object() {
     let a: Rc<u32> = Rc::new(4);
-    let a: Rc<Any> = a;  // Unsizing
+    let a: Rc<dyn Any> = a;  // Unsizing
 
     // Exercise is_dangling() with a DST
     let mut a = Rc::downgrade(&a);
@@ -49,7 +49,7 @@ fn trait_object() {
     let mut b = Weak::<u32>::new();
     b = b.clone();
     assert!(b.upgrade().is_none());
-    let mut b: Weak<Any> = b;  // Unsizing
+    let mut b: Weak<dyn Any> = b;  // Unsizing
     b = b.clone();
     assert!(b.upgrade().is_none());
 }
diff --git a/src/liballoc_jemalloc/lib.rs b/src/liballoc_jemalloc/lib.rs
index 413b212281b..b3b20715511 100644
--- a/src/liballoc_jemalloc/lib.rs
+++ b/src/liballoc_jemalloc/lib.rs
@@ -10,7 +10,6 @@
 
 #![no_std]
 #![allow(unused_attributes)]
-#![deny(bare_trait_objects)]
 #![unstable(feature = "alloc_jemalloc",
             reason = "implementation detail of std, does not provide any public API",
             issue = "0")]
diff --git a/src/liballoc_system/lib.rs b/src/liballoc_system/lib.rs
index c6c0abefbab..64348e05de7 100644
--- a/src/liballoc_system/lib.rs
+++ b/src/liballoc_system/lib.rs
@@ -10,7 +10,6 @@
 
 #![no_std]
 #![allow(unused_attributes)]
-#![deny(bare_trait_objects)]
 #![unstable(feature = "alloc_system",
             reason = "this library is unlikely to be stabilized in its current \
                       form or name",
diff --git a/src/libarena/lib.rs b/src/libarena/lib.rs
index 6f692923c85..0f4a5d16e17 100644
--- a/src/libarena/lib.rs
+++ b/src/libarena/lib.rs
@@ -30,7 +30,6 @@
 #![cfg_attr(test, feature(test))]
 
 #![allow(deprecated)]
-#![deny(bare_trait_objects)]
 
 extern crate alloc;
 extern crate rustc_data_structures;
diff --git a/src/libcore/any.rs b/src/libcore/any.rs
index 94f23db1ccc..6b26093439e 100644
--- a/src/libcore/any.rs
+++ b/src/libcore/any.rs
@@ -120,7 +120,7 @@ impl<T: 'static + ?Sized > Any for T {
 ///////////////////////////////////////////////////////////////////////////////
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl fmt::Debug for Any {
+impl fmt::Debug for dyn Any {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Any")
     }
@@ -130,20 +130,20 @@ impl fmt::Debug for Any {
 // hence used with `unwrap`. May eventually no longer be needed if
 // dispatch works with upcasting.
 #[stable(feature = "rust1", since = "1.0.0")]
-impl fmt::Debug for Any + Send {
+impl fmt::Debug for dyn Any + Send {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Any")
     }
 }
 
 #[stable(feature = "any_send_sync_methods", since = "1.28.0")]
-impl fmt::Debug for Any + Send + Sync {
+impl fmt::Debug for dyn Any + Send + Sync {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Any")
     }
 }
 
-impl Any {
+impl dyn Any {
     /// Returns `true` if the boxed type is the same as `T`.
     ///
     /// # Examples
@@ -203,7 +203,7 @@ impl Any {
     pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
         if self.is::<T>() {
             unsafe {
-                Some(&*(self as *const Any as *const T))
+                Some(&*(self as *const dyn Any as *const T))
             }
         } else {
             None
@@ -240,7 +240,7 @@ impl Any {
     pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
         if self.is::<T>() {
             unsafe {
-                Some(&mut *(self as *mut Any as *mut T))
+                Some(&mut *(self as *mut dyn Any as *mut T))
             }
         } else {
             None
@@ -248,7 +248,7 @@ impl Any {
     }
 }
 
-impl Any+Send {
+impl dyn Any+Send {
     /// Forwards to the method defined on the type `Any`.
     ///
     /// # Examples
@@ -332,7 +332,7 @@ impl Any+Send {
     }
 }
 
-impl Any+Send+Sync {
+impl dyn Any+Send+Sync {
     /// Forwards to the method defined on the type `Any`.
     ///
     /// # Examples
diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs
index b6087628ea6..137e9fe2c15 100644
--- a/src/libcore/cell.rs
+++ b/src/libcore/cell.rs
@@ -1532,7 +1532,7 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
 
 #[allow(unused)]
 fn assert_coerce_unsized(a: UnsafeCell<&i32>, b: Cell<&i32>, c: RefCell<&i32>) {
-    let _: UnsafeCell<&Send> = a;
-    let _: Cell<&Send> = b;
-    let _: RefCell<&Send> = c;
+    let _: UnsafeCell<&dyn Send> = a;
+    let _: Cell<&dyn Send> = b;
+    let _: RefCell<&dyn Send> = c;
 }
diff --git a/src/libcore/fmt/builders.rs b/src/libcore/fmt/builders.rs
index e8ea2e743da..3c5f934d4d8 100644
--- a/src/libcore/fmt/builders.rs
+++ b/src/libcore/fmt/builders.rs
@@ -11,7 +11,7 @@
 use fmt;
 
 struct PadAdapter<'a> {
-    buf: &'a mut (fmt::Write + 'a),
+    buf: &'a mut (dyn fmt::Write + 'a),
     on_newline: bool,
 }
 
@@ -107,7 +107,7 @@ pub fn debug_struct_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>,
 impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
     /// Adds a new field to the generated struct output.
     #[stable(feature = "debug_builders", since = "1.2.0")]
-    pub fn field(&mut self, name: &str, value: &fmt::Debug) -> &mut DebugStruct<'a, 'b> {
+    pub fn field(&mut self, name: &str, value: &dyn fmt::Debug) -> &mut DebugStruct<'a, 'b> {
         self.result = self.result.and_then(|_| {
             let prefix = if self.has_fields {
                 ","
@@ -204,7 +204,7 @@ pub fn debug_tuple_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> D
 impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
     /// Adds a new field to the generated tuple struct output.
     #[stable(feature = "debug_builders", since = "1.2.0")]
-    pub fn field(&mut self, value: &fmt::Debug) -> &mut DebugTuple<'a, 'b> {
+    pub fn field(&mut self, value: &dyn fmt::Debug) -> &mut DebugTuple<'a, 'b> {
         self.result = self.result.and_then(|_| {
             let (prefix, space) = if self.fields > 0 {
                 (",", " ")
@@ -258,7 +258,7 @@ struct DebugInner<'a, 'b: 'a> {
 }
 
 impl<'a, 'b: 'a> DebugInner<'a, 'b> {
-    fn entry(&mut self, entry: &fmt::Debug) {
+    fn entry(&mut self, entry: &dyn fmt::Debug) {
         self.result = self.result.and_then(|_| {
             if self.is_pretty() {
                 let mut slot = None;
@@ -340,7 +340,7 @@ pub fn debug_set_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugSet<'a, 'b
 impl<'a, 'b: 'a> DebugSet<'a, 'b> {
     /// Adds a new entry to the set output.
     #[stable(feature = "debug_builders", since = "1.2.0")]
-    pub fn entry(&mut self, entry: &fmt::Debug) -> &mut DebugSet<'a, 'b> {
+    pub fn entry(&mut self, entry: &dyn fmt::Debug) -> &mut DebugSet<'a, 'b> {
         self.inner.entry(entry);
         self
     }
@@ -411,7 +411,7 @@ pub fn debug_list_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugList<'a,
 impl<'a, 'b: 'a> DebugList<'a, 'b> {
     /// Adds a new entry to the list output.
     #[stable(feature = "debug_builders", since = "1.2.0")]
-    pub fn entry(&mut self, entry: &fmt::Debug) -> &mut DebugList<'a, 'b> {
+    pub fn entry(&mut self, entry: &dyn fmt::Debug) -> &mut DebugList<'a, 'b> {
         self.inner.entry(entry);
         self
     }
@@ -482,7 +482,7 @@ pub fn debug_map_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugMap<'a, 'b
 impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     /// Adds a new entry to the map output.
     #[stable(feature = "debug_builders", since = "1.2.0")]
-    pub fn entry(&mut self, key: &fmt::Debug, value: &fmt::Debug) -> &mut DebugMap<'a, 'b> {
+    pub fn entry(&mut self, key: &dyn fmt::Debug, value: &dyn fmt::Debug) -> &mut DebugMap<'a, 'b> {
         self.result = self.result.and_then(|_| {
             if self.is_pretty() {
                 let mut slot = None;
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index d91bf463383..928f95e3ba2 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -255,7 +255,7 @@ pub struct Formatter<'a> {
     width: Option<usize>,
     precision: Option<usize>,
 
-    buf: &'a mut (Write+'a),
+    buf: &'a mut (dyn Write+'a),
     curarg: slice::Iter<'a, ArgumentV1<'a>>,
     args: &'a [ArgumentV1<'a>],
 }
@@ -272,7 +272,7 @@ struct Void {
     ///
     /// It was added after #45197 showed that one could share a `!Sync`
     /// object across threads by passing it into `format_args!`.
-    _oibit_remover: PhantomData<*mut Fn()>,
+    _oibit_remover: PhantomData<*mut dyn Fn()>,
 }
 
 /// This struct represents the generic "argument" which is taken by the Xprintf
@@ -1020,7 +1020,7 @@ pub trait UpperExp {
 ///
 /// [`write!`]: ../../std/macro.write.html
 #[stable(feature = "rust1", since = "1.0.0")]
-pub fn write(output: &mut Write, args: Arguments) -> Result {
+pub fn write(output: &mut dyn Write, args: Arguments) -> Result {
     let mut formatter = Formatter {
         flags: 0,
         width: None,
@@ -1062,7 +1062,7 @@ pub fn write(output: &mut Write, args: Arguments) -> Result {
 
 impl<'a> Formatter<'a> {
     fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c>
-        where 'b: 'c, F: FnOnce(&'b mut (Write+'b)) -> &'c mut (Write+'c)
+        where 'b: 'c, F: FnOnce(&'b mut (dyn Write+'b)) -> &'c mut (dyn Write+'c)
     {
         Formatter {
             // We want to change this
@@ -1342,7 +1342,7 @@ impl<'a> Formatter<'a> {
     }
 
     fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
-        fn write_bytes(buf: &mut Write, s: &[u8]) -> Result {
+        fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result {
             buf.write_str(unsafe { str::from_utf8_unchecked(s) })
         }
 
diff --git a/src/libcore/iter/iterator.rs b/src/libcore/iter/iterator.rs
index afc273d265b..48c6eb94144 100644
--- a/src/libcore/iter/iterator.rs
+++ b/src/libcore/iter/iterator.rs
@@ -18,7 +18,7 @@ use super::{Inspect, Map, Peekable, Scan, Skip, SkipWhile, StepBy, Take, TakeWhi
 use super::{Zip, Sum, Product};
 use super::{ChainState, FromIterator, ZipImpl};
 
-fn _assert_is_object_safe(_: &Iterator<Item=()>) {}
+fn _assert_is_object_safe(_: &dyn Iterator<Item=()>) {}
 
 /// An interface for dealing with iterators.
 ///
diff --git a/src/libcore/panic.rs b/src/libcore/panic.rs
index 10f02ca2fdc..17cac5aa0a0 100644
--- a/src/libcore/panic.rs
+++ b/src/libcore/panic.rs
@@ -43,7 +43,7 @@ use fmt;
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 #[derive(Debug)]
 pub struct PanicInfo<'a> {
-    payload: &'a (Any + Send),
+    payload: &'a (dyn Any + Send),
     message: Option<&'a fmt::Arguments<'a>>,
     location: Location<'a>,
 }
@@ -64,7 +64,7 @@ impl<'a> PanicInfo<'a> {
 
     #[doc(hidden)]
     #[inline]
-    pub fn set_payload(&mut self, info: &'a (Any + Send)) {
+    pub fn set_payload(&mut self, info: &'a (dyn Any + Send)) {
         self.payload = info;
     }
 
@@ -86,7 +86,7 @@ impl<'a> PanicInfo<'a> {
     /// panic!("Normal panic");
     /// ```
     #[stable(feature = "panic_hooks", since = "1.10.0")]
-    pub fn payload(&self) -> &(Any + Send) {
+    pub fn payload(&self) -> &(dyn Any + Send) {
         self.payload
     }
 
@@ -270,6 +270,6 @@ impl<'a> fmt::Display for Location<'a> {
 #[unstable(feature = "std_internals", issue = "0")]
 #[doc(hidden)]
 pub unsafe trait BoxMeUp {
-    fn box_me_up(&mut self) -> *mut (Any + Send);
-    fn get(&mut self) -> &(Any + Send);
+    fn box_me_up(&mut self) -> *mut (dyn Any + Send);
+    fn get(&mut self) -> &(dyn Any + Send);
 }
diff --git a/src/libcore/task/context.rs b/src/libcore/task/context.rs
index c69d45248a5..1fc975cb178 100644
--- a/src/libcore/task/context.rs
+++ b/src/libcore/task/context.rs
@@ -21,7 +21,7 @@ use super::{Executor, Waker, LocalWaker};
 /// when performing a single `poll` step on a task.
 pub struct Context<'a> {
     local_waker: &'a LocalWaker,
-    executor: &'a mut Executor,
+    executor: &'a mut dyn Executor,
 }
 
 impl<'a> fmt::Debug for Context<'a> {
@@ -34,7 +34,7 @@ impl<'a> fmt::Debug for Context<'a> {
 impl<'a> Context<'a> {
     /// Create a new task `Context` with the provided `local_waker`, `waker`, and `executor`.
     #[inline]
-    pub fn new(local_waker: &'a LocalWaker, executor: &'a mut Executor) -> Context<'a> {
+    pub fn new(local_waker: &'a LocalWaker, executor: &'a mut dyn Executor) -> Context<'a> {
         Context {
             local_waker,
             executor,
@@ -58,7 +58,7 @@ impl<'a> Context<'a> {
     /// This method is useful primarily if you want to explicitly handle
     /// spawn failures.
     #[inline]
-    pub fn executor(&mut self) -> &mut Executor {
+    pub fn executor(&mut self) -> &mut dyn Executor {
         self.executor
     }
 
diff --git a/src/libcore/task/wake.rs b/src/libcore/task/wake.rs
index 3b901c9aef0..321b432d3f4 100644
--- a/src/libcore/task/wake.rs
+++ b/src/libcore/task/wake.rs
@@ -23,7 +23,7 @@ use ptr::NonNull;
 /// trait, allowing notifications to get routed through it.
 #[repr(transparent)]
 pub struct Waker {
-    inner: NonNull<UnsafeWake>,
+    inner: NonNull<dyn UnsafeWake>,
 }
 
 impl Unpin for Waker {}
@@ -41,7 +41,7 @@ impl Waker {
     /// use the `Waker::from` function instead which works with the safe
     /// `Arc` type and the safe `Wake` trait.
     #[inline]
-    pub unsafe fn new(inner: NonNull<UnsafeWake>) -> Self {
+    pub unsafe fn new(inner: NonNull<dyn UnsafeWake>) -> Self {
         Waker { inner: inner }
     }
 
@@ -98,7 +98,7 @@ impl Drop for Waker {
 /// behavior.
 #[repr(transparent)]
 pub struct LocalWaker {
-    inner: NonNull<UnsafeWake>,
+    inner: NonNull<dyn UnsafeWake>,
 }
 
 impl Unpin for LocalWaker {}
@@ -119,7 +119,7 @@ impl LocalWaker {
     /// For this function to be used safely, it must be sound to call `inner.wake_local()`
     /// on the current thread.
     #[inline]
-    pub unsafe fn new(inner: NonNull<UnsafeWake>) -> Self {
+    pub unsafe fn new(inner: NonNull<dyn UnsafeWake>) -> Self {
         LocalWaker { inner: inner }
     }
 
diff --git a/src/libcore/tests/any.rs b/src/libcore/tests/any.rs
index 2d3e81aa131..a80bf939530 100644
--- a/src/libcore/tests/any.rs
+++ b/src/libcore/tests/any.rs
@@ -17,7 +17,7 @@ static TEST: &'static str = "Test";
 
 #[test]
 fn any_referenced() {
-    let (a, b, c) = (&5 as &Any, &TEST as &Any, &Test as &Any);
+    let (a, b, c) = (&5 as &dyn Any, &TEST as &dyn Any, &Test as &dyn Any);
 
     assert!(a.is::<i32>());
     assert!(!b.is::<i32>());
@@ -34,7 +34,11 @@ fn any_referenced() {
 
 #[test]
 fn any_owning() {
-    let (a, b, c) = (box 5_usize as Box<Any>, box TEST as Box<Any>, box Test as Box<Any>);
+    let (a, b, c) = (
+        box 5_usize as Box<dyn Any>,
+        box TEST as Box<dyn Any>,
+        box Test as Box<dyn Any>,
+    );
 
     assert!(a.is::<usize>());
     assert!(!b.is::<usize>());
@@ -51,7 +55,7 @@ fn any_owning() {
 
 #[test]
 fn any_downcast_ref() {
-    let a = &5_usize as &Any;
+    let a = &5_usize as &dyn Any;
 
     match a.downcast_ref::<usize>() {
         Some(&5) => {}
@@ -69,9 +73,9 @@ fn any_downcast_mut() {
     let mut a = 5_usize;
     let mut b: Box<_> = box 7_usize;
 
-    let a_r = &mut a as &mut Any;
+    let a_r = &mut a as &mut dyn Any;
     let tmp: &mut usize = &mut *b;
-    let b_r = tmp as &mut Any;
+    let b_r = tmp as &mut dyn Any;
 
     match a_r.downcast_mut::<usize>() {
         Some(x) => {
@@ -113,7 +117,7 @@ fn any_downcast_mut() {
 #[test]
 fn any_fixed_vec() {
     let test = [0_usize; 8];
-    let test = &test as &Any;
+    let test = &test as &dyn Any;
     assert!(test.is::<[usize; 8]>());
     assert!(!test.is::<[usize; 10]>());
 }
diff --git a/src/libcore/tests/hash/mod.rs b/src/libcore/tests/hash/mod.rs
index 8716421b424..85c9d41b65b 100644
--- a/src/libcore/tests/hash/mod.rs
+++ b/src/libcore/tests/hash/mod.rs
@@ -128,7 +128,7 @@ fn test_custom_state() {
 fn test_indirect_hasher() {
     let mut hasher = MyHasher { hash: 0 };
     {
-        let mut indirect_hasher: &mut Hasher = &mut hasher;
+        let mut indirect_hasher: &mut dyn Hasher = &mut hasher;
         5u32.hash(&mut indirect_hasher);
     }
     assert_eq!(hasher.hash, 5);
diff --git a/src/libcore/tests/intrinsics.rs b/src/libcore/tests/intrinsics.rs
index 2b380abf63c..9f3cba26a62 100644
--- a/src/libcore/tests/intrinsics.rs
+++ b/src/libcore/tests/intrinsics.rs
@@ -22,7 +22,7 @@ fn test_typeid_sized_types() {
 #[test]
 fn test_typeid_unsized_types() {
     trait Z {}
-    struct X(str); struct Y(Z + 'static);
+    struct X(str); struct Y(dyn Z + 'static);
 
     assert_eq!(TypeId::of::<X>(), TypeId::of::<X>());
     assert_eq!(TypeId::of::<Y>(), TypeId::of::<Y>());
diff --git a/src/libcore/tests/mem.rs b/src/libcore/tests/mem.rs
index f55a1c81463..714f2babbdf 100644
--- a/src/libcore/tests/mem.rs
+++ b/src/libcore/tests/mem.rs
@@ -109,11 +109,11 @@ fn test_transmute() {
     trait Foo { fn dummy(&self) { } }
     impl Foo for isize {}
 
-    let a = box 100isize as Box<Foo>;
+    let a = box 100isize as Box<dyn Foo>;
     unsafe {
         let x: ::core::raw::TraitObject = transmute(a);
         assert!(*(x.data as *const isize) == 100);
-        let _x: Box<Foo> = transmute(x);
+        let _x: Box<dyn Foo> = transmute(x);
     }
 
     unsafe {
diff --git a/src/libcore/tests/option.rs b/src/libcore/tests/option.rs
index bc3e61a4f54..324ebf43565 100644
--- a/src/libcore/tests/option.rs
+++ b/src/libcore/tests/option.rs
@@ -240,7 +240,7 @@ fn test_collect() {
     assert!(v == None);
 
     // test that it does not take more elements than it needs
-    let mut functions: [Box<Fn() -> Option<()>>; 3] =
+    let mut functions: [Box<dyn Fn() -> Option<()>>; 3] =
         [box || Some(()), box || None, box || panic!()];
 
     let v: Option<Vec<()>> = functions.iter_mut().map(|f| (*f)()).collect();
diff --git a/src/libcore/tests/ptr.rs b/src/libcore/tests/ptr.rs
index 31bc1d67768..92160910d8f 100644
--- a/src/libcore/tests/ptr.rs
+++ b/src/libcore/tests/ptr.rs
@@ -84,16 +84,16 @@ fn test_is_null() {
     assert!(nms.is_null());
 
     // Pointers to unsized types -- trait objects
-    let ci: *const ToString = &3;
+    let ci: *const dyn ToString = &3;
     assert!(!ci.is_null());
 
-    let mi: *mut ToString = &mut 3;
+    let mi: *mut dyn ToString = &mut 3;
     assert!(!mi.is_null());
 
-    let nci: *const ToString = null::<isize>();
+    let nci: *const dyn ToString = null::<isize>();
     assert!(nci.is_null());
 
-    let nmi: *mut ToString = null_mut::<isize>();
+    let nmi: *mut dyn ToString = null_mut::<isize>();
     assert!(nmi.is_null());
 }
 
@@ -140,16 +140,16 @@ fn test_as_ref() {
         assert_eq!(nms.as_ref(), None);
 
         // Pointers to unsized types -- trait objects
-        let ci: *const ToString = &3;
+        let ci: *const dyn ToString = &3;
         assert!(ci.as_ref().is_some());
 
-        let mi: *mut ToString = &mut 3;
+        let mi: *mut dyn ToString = &mut 3;
         assert!(mi.as_ref().is_some());
 
-        let nci: *const ToString = null::<isize>();
+        let nci: *const dyn ToString = null::<isize>();
         assert!(nci.as_ref().is_none());
 
-        let nmi: *mut ToString = null_mut::<isize>();
+        let nmi: *mut dyn ToString = null_mut::<isize>();
         assert!(nmi.as_ref().is_none());
     }
 }
@@ -182,10 +182,10 @@ fn test_as_mut() {
         assert_eq!(nms.as_mut(), None);
 
         // Pointers to unsized types -- trait objects
-        let mi: *mut ToString = &mut 3;
+        let mi: *mut dyn ToString = &mut 3;
         assert!(mi.as_mut().is_some());
 
-        let nmi: *mut ToString = null_mut::<isize>();
+        let nmi: *mut dyn ToString = null_mut::<isize>();
         assert!(nmi.as_mut().is_none());
     }
 }
diff --git a/src/libcore/tests/result.rs b/src/libcore/tests/result.rs
index d9927ce4487..0616252c82c 100644
--- a/src/libcore/tests/result.rs
+++ b/src/libcore/tests/result.rs
@@ -81,7 +81,7 @@ fn test_collect() {
     assert!(v == Err(2));
 
     // test that it does not take more elements than it needs
-    let mut functions: [Box<Fn() -> Result<(), isize>>; 3] =
+    let mut functions: [Box<dyn Fn() -> Result<(), isize>>; 3] =
         [box || Ok(()), box || Err(1), box || panic!()];
 
     let v: Result<Vec<()>, isize> = functions.iter_mut().map(|f| (*f)()).collect();
diff --git a/src/libfmt_macros/lib.rs b/src/libfmt_macros/lib.rs
index 30a3bbdc58e..3aa09a91e07 100644
--- a/src/libfmt_macros/lib.rs
+++ b/src/libfmt_macros/lib.rs
@@ -14,8 +14,6 @@
 //! Parsing does not happen at runtime: structures of `std::fmt::rt` are
 //! generated instead.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
diff --git a/src/libgraphviz/lib.rs b/src/libgraphviz/lib.rs
index 9e71ed4063e..158d0101515 100644
--- a/src/libgraphviz/lib.rs
+++ b/src/libgraphviz/lib.rs
@@ -283,8 +283,6 @@
 //!
 //! * [DOT language](http://www.graphviz.org/doc/info/lang.html)
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
diff --git a/src/libpanic_abort/lib.rs b/src/libpanic_abort/lib.rs
index 02ab28507d7..392bf17968f 100644
--- a/src/libpanic_abort/lib.rs
+++ b/src/libpanic_abort/lib.rs
@@ -21,7 +21,6 @@
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/")]
 #![panic_runtime]
 #![allow(unused_features)]
-#![deny(bare_trait_objects)]
 
 #![feature(core_intrinsics)]
 #![feature(libc)]
diff --git a/src/libpanic_unwind/lib.rs b/src/libpanic_unwind/lib.rs
index f8cd29fc086..5c320bb369e 100644
--- a/src/libpanic_unwind/lib.rs
+++ b/src/libpanic_unwind/lib.rs
@@ -22,7 +22,6 @@
 //! More documentation about each implementation can be found in the respective
 //! module.
 
-#![deny(bare_trait_objects)]
 #![no_std]
 #![unstable(feature = "panic_unwind", issue = "32837")]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
diff --git a/src/libproc_macro/lib.rs b/src/libproc_macro/lib.rs
index 61da9db76f6..bf6e4a3aaa4 100644
--- a/src/libproc_macro/lib.rs
+++ b/src/libproc_macro/lib.rs
@@ -22,7 +22,6 @@
 //! See [the book](../book/first-edition/procedural-macros.html) for more.
 
 #![stable(feature = "proc_macro_lib", since = "1.15.0")]
-#![deny(bare_trait_objects)]
 #![deny(missing_docs)]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
diff --git a/src/libprofiler_builtins/lib.rs b/src/libprofiler_builtins/lib.rs
index 3d91505cd77..6d0d6d115b7 100644
--- a/src/libprofiler_builtins/lib.rs
+++ b/src/libprofiler_builtins/lib.rs
@@ -15,5 +15,4 @@
             reason = "internal implementation detail of rustc right now",
             issue = "0")]
 #![allow(unused_features)]
-#![deny(bare_trait_objects)]
 #![feature(staged_api)]
diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index d709a4debd1..b6cb336648b 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -36,8 +36,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_allocator/lib.rs b/src/librustc_allocator/lib.rs
index 1227936ce96..b217d3665a2 100644
--- a/src/librustc_allocator/lib.rs
+++ b/src/librustc_allocator/lib.rs
@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
 #![feature(rustc_private)]
 
 #[macro_use] extern crate log;
diff --git a/src/librustc_apfloat/lib.rs b/src/librustc_apfloat/lib.rs
index c7cd958016d..08438805a70 100644
--- a/src/librustc_apfloat/lib.rs
+++ b/src/librustc_apfloat/lib.rs
@@ -40,8 +40,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_asan/lib.rs b/src/librustc_asan/lib.rs
index 7bd1e98f85d..0c78fd74a23 100644
--- a/src/librustc_asan/lib.rs
+++ b/src/librustc_asan/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![sanitizer_runtime]
 #![feature(alloc_system)]
 #![feature(sanitizer_runtime)]
diff --git a/src/librustc_borrowck/lib.rs b/src/librustc_borrowck/lib.rs
index d583a32c431..a5a20af0e4e 100644
--- a/src/librustc_borrowck/lib.rs
+++ b/src/librustc_borrowck/lib.rs
@@ -13,7 +13,6 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![allow(non_camel_case_types)]
-#![deny(bare_trait_objects)]
 
 #![feature(from_ref)]
 #![feature(quote)]
diff --git a/src/librustc_codegen_llvm/lib.rs b/src/librustc_codegen_llvm/lib.rs
index 8aa7902021f..90f96c9687b 100644
--- a/src/librustc_codegen_llvm/lib.rs
+++ b/src/librustc_codegen_llvm/lib.rs
@@ -23,7 +23,6 @@
 #![feature(custom_attribute)]
 #![feature(fs_read_write)]
 #![allow(unused_attributes)]
-#![deny(bare_trait_objects)]
 #![feature(libc)]
 #![feature(quote)]
 #![feature(range_contains)]
diff --git a/src/librustc_codegen_utils/lib.rs b/src/librustc_codegen_utils/lib.rs
index e9031007a4e..f59cf5832fc 100644
--- a/src/librustc_codegen_utils/lib.rs
+++ b/src/librustc_codegen_utils/lib.rs
@@ -20,7 +20,6 @@
 #![feature(box_syntax)]
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
-#![deny(bare_trait_objects)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index ef0d57c7b7c..a9e582e510e 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -16,8 +16,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://www.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_driver/lib.rs b/src/librustc_driver/lib.rs
index 000025c49a6..9e818641dec 100644
--- a/src/librustc_driver/lib.rs
+++ b/src/librustc_driver/lib.rs
@@ -14,8 +14,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index c0f07645f49..67d2aa4d770 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_incremental/lib.rs b/src/librustc_incremental/lib.rs
index 2ef88041d33..3839c133a6e 100644
--- a/src/librustc_incremental/lib.rs
+++ b/src/librustc_incremental/lib.rs
@@ -10,8 +10,6 @@
 
 //! Support for serializing the dep-graph and reloading it.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 798c289ac2f..78a8c494f48 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -19,8 +19,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_llvm/lib.rs b/src/librustc_llvm/lib.rs
index c60016cde0d..741758cb954 100644
--- a/src/librustc_llvm/lib.rs
+++ b/src/librustc_llvm/lib.rs
@@ -12,7 +12,6 @@
 #![allow(non_camel_case_types)]
 #![allow(non_snake_case)]
 #![allow(dead_code)]
-#![deny(bare_trait_objects)]
 
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
diff --git a/src/librustc_lsan/lib.rs b/src/librustc_lsan/lib.rs
index 7bd1e98f85d..0c78fd74a23 100644
--- a/src/librustc_lsan/lib.rs
+++ b/src/librustc_lsan/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![sanitizer_runtime]
 #![feature(alloc_system)]
 #![feature(sanitizer_runtime)]
diff --git a/src/librustc_metadata/lib.rs b/src/librustc_metadata/lib.rs
index d535c1ef903..5cba0387d17 100644
--- a/src/librustc_metadata/lib.rs
+++ b/src/librustc_metadata/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_mir/lib.rs b/src/librustc_mir/lib.rs
index 382248c2d15..54730ecd75f 100644
--- a/src/librustc_mir/lib.rs
+++ b/src/librustc_mir/lib.rs
@@ -14,8 +14,6 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 
 */
 
-#![deny(bare_trait_objects)]
-
 #![feature(slice_patterns)]
 #![feature(slice_sort_by_cached_key)]
 #![feature(from_ref)]
diff --git a/src/librustc_msan/lib.rs b/src/librustc_msan/lib.rs
index 7bd1e98f85d..0c78fd74a23 100644
--- a/src/librustc_msan/lib.rs
+++ b/src/librustc_msan/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![sanitizer_runtime]
 #![feature(alloc_system)]
 #![feature(sanitizer_runtime)]
diff --git a/src/librustc_passes/lib.rs b/src/librustc_passes/lib.rs
index 15d7c0fdaa3..41f1e782965 100644
--- a/src/librustc_passes/lib.rs
+++ b/src/librustc_passes/lib.rs
@@ -14,8 +14,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_platform_intrinsics/lib.rs b/src/librustc_platform_intrinsics/lib.rs
index 92e83fd70fa..b57debdd994 100644
--- a/src/librustc_platform_intrinsics/lib.rs
+++ b/src/librustc_platform_intrinsics/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![allow(bad_style)]
-#![deny(bare_trait_objects)]
 
 pub struct Intrinsic {
     pub inputs: &'static [&'static Type],
diff --git a/src/librustc_plugin/lib.rs b/src/librustc_plugin/lib.rs
index b2c492f204f..348aa6a7cef 100644
--- a/src/librustc_plugin/lib.rs
+++ b/src/librustc_plugin/lib.rs
@@ -60,8 +60,6 @@
 //! See the [`plugin` feature](../unstable-book/language-features/plugin.html) of
 //! the Unstable Book for more examples.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_privacy/lib.rs b/src/librustc_privacy/lib.rs
index 7b13c98b31d..405952065da 100644
--- a/src/librustc_privacy/lib.rs
+++ b/src/librustc_privacy/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 765016fdc4a..8130c4e8326 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_save_analysis/lib.rs b/src/librustc_save_analysis/lib.rs
index c84f194f023..a250d4a3598 100644
--- a/src/librustc_save_analysis/lib.rs
+++ b/src/librustc_save_analysis/lib.rs
@@ -13,7 +13,6 @@
        html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
-#![deny(bare_trait_objects)]
 
 #![recursion_limit="256"]
 
diff --git a/src/librustc_target/lib.rs b/src/librustc_target/lib.rs
index e611d26da56..8f491157439 100644
--- a/src/librustc_target/lib.rs
+++ b/src/librustc_target/lib.rs
@@ -21,8 +21,6 @@
 //! one that doesn't; the one that doesn't might get decent parallel
 //! build speedups.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/librustc_traits/lib.rs b/src/librustc_traits/lib.rs
index 2a4cacb5623..d17cf35f181 100644
--- a/src/librustc_traits/lib.rs
+++ b/src/librustc_traits/lib.rs
@@ -11,8 +11,6 @@
 //! New recursive solver modeled on Chalk's recursive solver. Most of
 //! the guts are broken up into modules; see the comments in those modules.
 
-#![deny(bare_trait_objects)]
-
 #![feature(crate_in_paths)]
 #![feature(crate_visibility_modifier)]
 #![feature(extern_prelude)]
diff --git a/src/librustc_tsan/lib.rs b/src/librustc_tsan/lib.rs
index 7bd1e98f85d..0c78fd74a23 100644
--- a/src/librustc_tsan/lib.rs
+++ b/src/librustc_tsan/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![sanitizer_runtime]
 #![feature(alloc_system)]
 #![feature(sanitizer_runtime)]
diff --git a/src/librustc_typeck/lib.rs b/src/librustc_typeck/lib.rs
index e343fb1a57b..6bf1ec8f697 100644
--- a/src/librustc_typeck/lib.rs
+++ b/src/librustc_typeck/lib.rs
@@ -70,7 +70,6 @@ This API is completely unstable and subject to change.
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![allow(non_camel_case_types)]
-#![deny(bare_trait_objects)]
 
 #![feature(box_patterns)]
 #![feature(box_syntax)]
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 98684b27973..c601f138d0a 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -375,7 +375,7 @@ impl fmt::Debug for Item {
 
         let fake = MAX_DEF_ID.with(|m| m.borrow().get(&self.def_id.krate)
                                    .map(|id| self.def_id >= *id).unwrap_or(false));
-        let def_id: &fmt::Debug = if fake { &"**FAKE**" } else { &self.def_id };
+        let def_id: &dyn fmt::Debug = if fake { &"**FAKE**" } else { &self.def_id };
 
         fmt.debug_struct("Item")
             .field("source", &self.source)
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 6e1b4589547..4b8dbaf4211 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -55,7 +55,7 @@ pub struct DocContext<'a, 'tcx: 'a, 'rcx: 'a> {
     /// The stack of module NodeIds up till this point
     pub mod_ids: RefCell<Vec<NodeId>>,
     pub crate_name: Option<String>,
-    pub cstore: Rc<CrateStore>,
+    pub cstore: Rc<dyn CrateStore>,
     pub populated_all_crate_impls: Cell<bool>,
     // Note that external items for which `doc(hidden)` applies to are shown as
     // non-reachable while local items aren't. This is because we're reusing
diff --git a/src/librustdoc/html/highlight.rs b/src/librustdoc/html/highlight.rs
index 5939d5341e3..6cf9b143373 100644
--- a/src/librustdoc/html/highlight.rs
+++ b/src/librustdoc/html/highlight.rs
@@ -395,7 +395,7 @@ impl Class {
 
 fn write_header(class: Option<&str>,
                 id: Option<&str>,
-                out: &mut Write)
+                out: &mut dyn Write)
                 -> io::Result<()> {
     write!(out, "<pre ")?;
     if let Some(id) = id {
@@ -404,6 +404,6 @@ fn write_header(class: Option<&str>,
     write!(out, "class=\"rust {}\">\n", class.unwrap_or(""))
 }
 
-fn write_footer(out: &mut Write) -> io::Result<()> {
+fn write_footer(out: &mut dyn Write) -> io::Result<()> {
     write!(out, "</pre>\n")
 }
diff --git a/src/librustdoc/html/layout.rs b/src/librustdoc/html/layout.rs
index 5e93b20ea17..af7c0a04215 100644
--- a/src/librustdoc/html/layout.rs
+++ b/src/librustdoc/html/layout.rs
@@ -32,7 +32,7 @@ pub struct Page<'a> {
 }
 
 pub fn render<T: fmt::Display, S: fmt::Display>(
-    dst: &mut io::Write, layout: &Layout, page: &Page, sidebar: &S, t: &T,
+    dst: &mut dyn io::Write, layout: &Layout, page: &Page, sidebar: &S, t: &T,
     css_file_extension: bool, themes: &[PathBuf])
     -> io::Result<()>
 {
@@ -194,7 +194,7 @@ pub fn render<T: fmt::Display, S: fmt::Display>(
     )
 }
 
-pub fn redirect(dst: &mut io::Write, url: &str) -> io::Result<()> {
+pub fn redirect(dst: &mut dyn io::Write, url: &str) -> io::Result<()> {
     // <script> triggers a redirect before refresh, so this is fine.
     write!(dst,
 r##"<!DOCTYPE html>
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index ade33c8dd7d..f137f4acf44 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -1822,7 +1822,7 @@ impl Context {
     }
 
     fn render_item(&self,
-                   writer: &mut io::Write,
+                   writer: &mut dyn io::Write,
                    it: &clean::Item,
                    pushname: bool)
                    -> io::Result<()> {
diff --git a/src/librustdoc/test.rs b/src/librustdoc/test.rs
index eb980a7369b..2966b9e9819 100644
--- a/src/librustdoc/test.rs
+++ b/src/librustdoc/test.rs
@@ -249,7 +249,7 @@ fn run_test(test: &str, cratename: &str, filename: &FileName, line: usize,
         }
         fn flush(&mut self) -> io::Result<()> { Ok(()) }
     }
-    struct Bomb(Arc<Mutex<Vec<u8>>>, Box<Write+Send>);
+    struct Bomb(Arc<Mutex<Vec<u8>>>, Box<dyn Write+Send>);
     impl Drop for Bomb {
         fn drop(&mut self) {
             let _ = self.1.write_all(&self.0.lock().unwrap());
diff --git a/src/libserialize/lib.rs b/src/libserialize/lib.rs
index 7c1bb69434d..a5f4b32b329 100644
--- a/src/libserialize/lib.rs
+++ b/src/libserialize/lib.rs
@@ -14,8 +14,6 @@
 Core encoding and decoding interfaces.
 */
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
diff --git a/src/libstd/error.rs b/src/libstd/error.rs
index 1958915602f..29534696abc 100644
--- a/src/libstd/error.rs
+++ b/src/libstd/error.rs
@@ -138,7 +138,7 @@ pub trait Error: Debug + Display {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    fn cause(&self) -> Option<&Error> { None }
+    fn cause(&self) -> Option<&dyn Error> { None }
 
     /// Get the `TypeId` of `self`
     #[doc(hidden)]
@@ -151,22 +151,22 @@ pub trait Error: Debug + Display {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, E: Error + 'a> From<E> for Box<Error + 'a> {
-    fn from(err: E) -> Box<Error + 'a> {
+impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
+    fn from(err: E) -> Box<dyn Error + 'a> {
         Box::new(err)
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<Error + Send + Sync + 'a> {
-    fn from(err: E) -> Box<Error + Send + Sync + 'a> {
+impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
+    fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
         Box::new(err)
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl From<String> for Box<Error + Send + Sync> {
-    fn from(err: String) -> Box<Error + Send + Sync> {
+impl From<String> for Box<dyn Error + Send + Sync> {
+    fn from(err: String) -> Box<dyn Error + Send + Sync> {
         #[derive(Debug)]
         struct StringError(String);
 
@@ -185,38 +185,38 @@ impl From<String> for Box<Error + Send + Sync> {
 }
 
 #[stable(feature = "string_box_error", since = "1.6.0")]
-impl From<String> for Box<Error> {
-    fn from(str_err: String) -> Box<Error> {
-        let err1: Box<Error + Send + Sync> = From::from(str_err);
-        let err2: Box<Error> = err1;
+impl From<String> for Box<dyn Error> {
+    fn from(str_err: String) -> Box<dyn Error> {
+        let err1: Box<dyn Error + Send + Sync> = From::from(str_err);
+        let err2: Box<dyn Error> = err1;
         err2
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, 'b> From<&'b str> for Box<Error + Send + Sync + 'a> {
-    fn from(err: &'b str) -> Box<Error + Send + Sync + 'a> {
+impl<'a, 'b> From<&'b str> for Box<dyn Error + Send + Sync + 'a> {
+    fn from(err: &'b str) -> Box<dyn Error + Send + Sync + 'a> {
         From::from(String::from(err))
     }
 }
 
 #[stable(feature = "string_box_error", since = "1.6.0")]
-impl<'a> From<&'a str> for Box<Error> {
-    fn from(err: &'a str) -> Box<Error> {
+impl<'a> From<&'a str> for Box<dyn Error> {
+    fn from(err: &'a str) -> Box<dyn Error> {
         From::from(String::from(err))
     }
 }
 
 #[stable(feature = "cow_box_error", since = "1.22.0")]
-impl<'a, 'b> From<Cow<'b, str>> for Box<Error + Send + Sync + 'a> {
-    fn from(err: Cow<'b, str>) -> Box<Error + Send + Sync + 'a> {
+impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
+    fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> {
         From::from(String::from(err))
     }
 }
 
 #[stable(feature = "cow_box_error", since = "1.22.0")]
-impl<'a> From<Cow<'a, str>> for Box<Error> {
-    fn from(err: Cow<'a, str>) -> Box<Error> {
+impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
+    fn from(err: Cow<'a, str>) -> Box<dyn Error> {
         From::from(String::from(err))
     }
 }
@@ -327,7 +327,7 @@ impl<T: Error> Error for Box<T> {
         Error::description(&**self)
     }
 
-    fn cause(&self) -> Option<&Error> {
+    fn cause(&self) -> Option<&dyn Error> {
         Error::cause(&**self)
     }
 }
@@ -368,7 +368,7 @@ impl Error for char::ParseCharError {
 }
 
 // copied from any.rs
-impl Error + 'static {
+impl dyn Error + 'static {
     /// Returns true if the boxed type is the same as `T`
     #[stable(feature = "error_downcast", since = "1.3.0")]
     #[inline]
@@ -390,7 +390,7 @@ impl Error + 'static {
     pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
         if self.is::<T>() {
             unsafe {
-                Some(&*(self as *const Error as *const T))
+                Some(&*(self as *const dyn Error as *const T))
             }
         } else {
             None
@@ -404,7 +404,7 @@ impl Error + 'static {
     pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
         if self.is::<T>() {
             unsafe {
-                Some(&mut *(self as *mut Error as *mut T))
+                Some(&mut *(self as *mut dyn Error as *mut T))
             }
         } else {
             None
@@ -412,60 +412,60 @@ impl Error + 'static {
     }
 }
 
-impl Error + 'static + Send {
+impl dyn Error + 'static + Send {
     /// Forwards to the method defined on the type `Any`.
     #[stable(feature = "error_downcast", since = "1.3.0")]
     #[inline]
     pub fn is<T: Error + 'static>(&self) -> bool {
-        <Error + 'static>::is::<T>(self)
+        <dyn Error + 'static>::is::<T>(self)
     }
 
     /// Forwards to the method defined on the type `Any`.
     #[stable(feature = "error_downcast", since = "1.3.0")]
     #[inline]
     pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
-        <Error + 'static>::downcast_ref::<T>(self)
+        <dyn Error + 'static>::downcast_ref::<T>(self)
     }
 
     /// Forwards to the method defined on the type `Any`.
     #[stable(feature = "error_downcast", since = "1.3.0")]
     #[inline]
     pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
-        <Error + 'static>::downcast_mut::<T>(self)
+        <dyn Error + 'static>::downcast_mut::<T>(self)
     }
 }
 
-impl Error + 'static + Send + Sync {
+impl dyn Error + 'static + Send + Sync {
     /// Forwards to the method defined on the type `Any`.
     #[stable(feature = "error_downcast", since = "1.3.0")]
     #[inline]
     pub fn is<T: Error + 'static>(&self) -> bool {
-        <Error + 'static>::is::<T>(self)
+        <dyn Error + 'static>::is::<T>(self)
     }
 
     /// Forwards to the method defined on the type `Any`.
     #[stable(feature = "error_downcast", since = "1.3.0")]
     #[inline]
     pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
-        <Error + 'static>::downcast_ref::<T>(self)
+        <dyn Error + 'static>::downcast_ref::<T>(self)
     }
 
     /// Forwards to the method defined on the type `Any`.
     #[stable(feature = "error_downcast", since = "1.3.0")]
     #[inline]
     pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
-        <Error + 'static>::downcast_mut::<T>(self)
+        <dyn Error + 'static>::downcast_mut::<T>(self)
     }
 }
 
-impl Error {
+impl dyn Error {
     #[inline]
     #[stable(feature = "error_downcast", since = "1.3.0")]
     /// Attempt to downcast the box to a concrete type.
-    pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Error>> {
+    pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error>> {
         if self.is::<T>() {
             unsafe {
-                let raw: *mut Error = Box::into_raw(self);
+                let raw: *mut dyn Error = Box::into_raw(self);
                 Ok(Box::from_raw(raw as *mut T))
             }
         } else {
@@ -474,30 +474,30 @@ impl Error {
     }
 }
 
-impl Error + Send {
+impl dyn Error + Send {
     #[inline]
     #[stable(feature = "error_downcast", since = "1.3.0")]
     /// Attempt to downcast the box to a concrete type.
     pub fn downcast<T: Error + 'static>(self: Box<Self>)
-                                        -> Result<Box<T>, Box<Error + Send>> {
-        let err: Box<Error> = self;
-        <Error>::downcast(err).map_err(|s| unsafe {
+                                        -> Result<Box<T>, Box<dyn Error + Send>> {
+        let err: Box<dyn Error> = self;
+        <dyn Error>::downcast(err).map_err(|s| unsafe {
             // reapply the Send marker
-            transmute::<Box<Error>, Box<Error + Send>>(s)
+            transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s)
         })
     }
 }
 
-impl Error + Send + Sync {
+impl dyn Error + Send + Sync {
     #[inline]
     #[stable(feature = "error_downcast", since = "1.3.0")]
     /// Attempt to downcast the box to a concrete type.
     pub fn downcast<T: Error + 'static>(self: Box<Self>)
                                         -> Result<Box<T>, Box<Self>> {
-        let err: Box<Error> = self;
-        <Error>::downcast(err).map_err(|s| unsafe {
+        let err: Box<dyn Error> = self;
+        <dyn Error>::downcast(err).map_err(|s| unsafe {
             // reapply the Send+Sync marker
-            transmute::<Box<Error>, Box<Error + Send + Sync>>(s)
+            transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s)
         })
     }
 }
@@ -533,13 +533,13 @@ mod tests {
     #[test]
     fn downcasting() {
         let mut a = A;
-        let a = &mut a as &mut (Error + 'static);
+        let a = &mut a as &mut (dyn Error + 'static);
         assert_eq!(a.downcast_ref::<A>(), Some(&A));
         assert_eq!(a.downcast_ref::<B>(), None);
         assert_eq!(a.downcast_mut::<A>(), Some(&mut A));
         assert_eq!(a.downcast_mut::<B>(), None);
 
-        let a: Box<Error> = Box::new(A);
+        let a: Box<dyn Error> = Box::new(A);
         match a.downcast::<B>() {
             Ok(..) => panic!("expected error"),
             Err(e) => assert_eq!(*e.downcast::<A>().unwrap(), A),
diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index b816f4b7850..754e2bbc412 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -891,7 +891,7 @@ impl Error for IntoStringError {
         "C string contained non-utf8 bytes"
     }
 
-    fn cause(&self) -> Option<&Error> {
+    fn cause(&self) -> Option<&dyn Error> {
         Some(&self.error)
     }
 }
diff --git a/src/libstd/io/error.rs b/src/libstd/io/error.rs
index bdd675e6e2b..02a3ce8b9c4 100644
--- a/src/libstd/io/error.rs
+++ b/src/libstd/io/error.rs
@@ -83,7 +83,7 @@ enum Repr {
 #[derive(Debug)]
 struct Custom {
     kind: ErrorKind,
-    error: Box<error::Error+Send+Sync>,
+    error: Box<dyn error::Error+Send+Sync>,
 }
 
 /// A list specifying general categories of I/O error.
@@ -250,12 +250,12 @@ impl Error {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new<E>(kind: ErrorKind, error: E) -> Error
-        where E: Into<Box<error::Error+Send+Sync>>
+        where E: Into<Box<dyn error::Error+Send+Sync>>
     {
         Self::_new(kind, error.into())
     }
 
-    fn _new(kind: ErrorKind, error: Box<error::Error+Send+Sync>) -> Error {
+    fn _new(kind: ErrorKind, error: Box<dyn error::Error+Send+Sync>) -> Error {
         Error {
             repr: Repr::Custom(Box::new(Custom {
                 kind,
@@ -373,7 +373,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "io_error_inner", since = "1.3.0")]
-    pub fn get_ref(&self) -> Option<&(error::Error+Send+Sync+'static)> {
+    pub fn get_ref(&self) -> Option<&(dyn error::Error+Send+Sync+'static)> {
         match self.repr {
             Repr::Os(..) => None,
             Repr::Simple(..) => None,
@@ -444,7 +444,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "io_error_inner", since = "1.3.0")]
-    pub fn get_mut(&mut self) -> Option<&mut (error::Error+Send+Sync+'static)> {
+    pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error+Send+Sync+'static)> {
         match self.repr {
             Repr::Os(..) => None,
             Repr::Simple(..) => None,
@@ -478,7 +478,7 @@ impl Error {
     /// }
     /// ```
     #[stable(feature = "io_error_inner", since = "1.3.0")]
-    pub fn into_inner(self) -> Option<Box<error::Error+Send+Sync>> {
+    pub fn into_inner(self) -> Option<Box<dyn error::Error+Send+Sync>> {
         match self.repr {
             Repr::Os(..) => None,
             Repr::Simple(..) => None,
@@ -551,7 +551,7 @@ impl error::Error for Error {
         }
     }
 
-    fn cause(&self) -> Option<&error::Error> {
+    fn cause(&self) -> Option<&dyn error::Error> {
         match self.repr {
             Repr::Os(..) => None,
             Repr::Simple(..) => None,
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 2b4644bd013..85304874848 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -1972,7 +1972,7 @@ impl<T: BufRead> BufRead for Take<T> {
     }
 }
 
-fn read_one_byte(reader: &mut Read) -> Option<Result<u8>> {
+fn read_one_byte(reader: &mut dyn Read) -> Option<Result<u8>> {
     let mut buf = [0];
     loop {
         return match reader.read(&mut buf) {
@@ -2081,7 +2081,7 @@ impl std_error::Error for CharsError {
             CharsError::Other(ref e) => std_error::Error::description(e),
         }
     }
-    fn cause(&self) -> Option<&std_error::Error> {
+    fn cause(&self) -> Option<&dyn std_error::Error> {
         match *self {
             CharsError::NotUtf8 => None,
             CharsError::Other(ref e) => e.cause(),
diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs
index fce85a200ba..fffe8fc559b 100644
--- a/src/libstd/io/stdio.rs
+++ b/src/libstd/io/stdio.rs
@@ -21,7 +21,7 @@ use thread::LocalKey;
 
 /// Stdout used by print! and println! macros
 thread_local! {
-    static LOCAL_STDOUT: RefCell<Option<Box<Write + Send>>> = {
+    static LOCAL_STDOUT: RefCell<Option<Box<dyn Write + Send>>> = {
         RefCell::new(None)
     }
 }
@@ -624,7 +624,7 @@ impl<'a> fmt::Debug for StderrLock<'a> {
                      with a more general mechanism",
            issue = "0")]
 #[doc(hidden)]
-pub fn set_panic(sink: Option<Box<Write + Send>>) -> Option<Box<Write + Send>> {
+pub fn set_panic(sink: Option<Box<dyn Write + Send>>) -> Option<Box<dyn Write + Send>> {
     use panicking::LOCAL_STDERR;
     use mem;
     LOCAL_STDERR.with(move |slot| {
@@ -648,7 +648,7 @@ pub fn set_panic(sink: Option<Box<Write + Send>>) -> Option<Box<Write + Send>> {
                      with a more general mechanism",
            issue = "0")]
 #[doc(hidden)]
-pub fn set_print(sink: Option<Box<Write + Send>>) -> Option<Box<Write + Send>> {
+pub fn set_print(sink: Option<Box<dyn Write + Send>>) -> Option<Box<dyn Write + Send>> {
     use mem;
     LOCAL_STDOUT.with(move |slot| {
         mem::replace(&mut *slot.borrow_mut(), sink)
@@ -670,7 +670,7 @@ pub fn set_print(sink: Option<Box<Write + Send>>) -> Option<Box<Write + Send>> {
 /// However, if the actual I/O causes an error, this function does panic.
 fn print_to<T>(
     args: fmt::Arguments,
-    local_s: &'static LocalKey<RefCell<Option<Box<Write+Send>>>>,
+    local_s: &'static LocalKey<RefCell<Option<Box<dyn Write+Send>>>>,
     global_s: fn() -> T,
     label: &str,
 )
diff --git a/src/libstd/io/util.rs b/src/libstd/io/util.rs
index 195310a26fe..33f741dbc38 100644
--- a/src/libstd/io/util.rs
+++ b/src/libstd/io/util.rs
@@ -223,7 +223,7 @@ mod tests {
         assert_eq!(copy(&mut r, &mut w).unwrap(), 4);
 
         let mut r = repeat(0).take(1 << 17);
-        assert_eq!(copy(&mut r as &mut Read, &mut w as &mut Write).unwrap(), 1 << 17);
+        assert_eq!(copy(&mut r as &mut dyn Read, &mut w as &mut dyn Write).unwrap(), 1 << 17);
     }
 
     #[test]
diff --git a/src/libstd/net/parser.rs b/src/libstd/net/parser.rs
index 008c5da171f..cf3e5354a31 100644
--- a/src/libstd/net/parser.rs
+++ b/src/libstd/net/parser.rs
@@ -58,7 +58,7 @@ impl<'a> Parser<'a> {
     }
 
     // Return result of first successful parser
-    fn read_or<T>(&mut self, parsers: &mut [Box<FnMut(&mut Parser) -> Option<T> + 'static>])
+    fn read_or<T>(&mut self, parsers: &mut [Box<dyn FnMut(&mut Parser) -> Option<T> + 'static>])
                -> Option<T> {
         for pf in parsers {
             if let Some(r) = self.read_atomically(|p: &mut Parser| pf(p)) {
diff --git a/src/libstd/net/tcp.rs b/src/libstd/net/tcp.rs
index 6b4bbdddf32..75c7a3d9280 100644
--- a/src/libstd/net/tcp.rs
+++ b/src/libstd/net/tcp.rs
@@ -927,7 +927,7 @@ mod tests {
     use time::{Instant, Duration};
     use thread;
 
-    fn each_ip(f: &mut FnMut(SocketAddr)) {
+    fn each_ip(f: &mut dyn FnMut(SocketAddr)) {
         f(next_test_ip4());
         f(next_test_ip6());
     }
diff --git a/src/libstd/net/udp.rs b/src/libstd/net/udp.rs
index d25e29999cb..0ebe3284b4f 100644
--- a/src/libstd/net/udp.rs
+++ b/src/libstd/net/udp.rs
@@ -826,7 +826,7 @@ mod tests {
     use time::{Instant, Duration};
     use thread;
 
-    fn each_ip(f: &mut FnMut(SocketAddr, SocketAddr)) {
+    fn each_ip(f: &mut dyn FnMut(SocketAddr, SocketAddr)) {
         f(next_test_ip4(), next_test_ip4());
         f(next_test_ip6(), next_test_ip6());
     }
diff --git a/src/libstd/panic.rs b/src/libstd/panic.rs
index 451420ae88a..b8c1c4f9e68 100644
--- a/src/libstd/panic.rs
+++ b/src/libstd/panic.rs
@@ -421,6 +421,6 @@ pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
 /// }
 /// ```
 #[stable(feature = "resume_unwind", since = "1.9.0")]
-pub fn resume_unwind(payload: Box<Any + Send>) -> ! {
+pub fn resume_unwind(payload: Box<dyn Any + Send>) -> ! {
     panicking::update_count_then_panic(payload)
 }
diff --git a/src/libstd/panicking.rs b/src/libstd/panicking.rs
index 46b6cf60705..283fd36af41 100644
--- a/src/libstd/panicking.rs
+++ b/src/libstd/panicking.rs
@@ -36,7 +36,7 @@ use sys_common::util;
 use thread;
 
 thread_local! {
-    pub static LOCAL_STDERR: RefCell<Option<Box<Write + Send>>> = {
+    pub static LOCAL_STDERR: RefCell<Option<Box<dyn Write + Send>>> = {
         RefCell::new(None)
     }
 }
@@ -64,7 +64,7 @@ extern {
 #[derive(Copy, Clone)]
 enum Hook {
     Default,
-    Custom(*mut (Fn(&PanicInfo) + 'static + Sync + Send)),
+    Custom(*mut (dyn Fn(&PanicInfo) + 'static + Sync + Send)),
 }
 
 static HOOK_LOCK: RWLock = RWLock::new();
@@ -104,7 +104,7 @@ static mut HOOK: Hook = Hook::Default;
 /// panic!("Normal panic");
 /// ```
 #[stable(feature = "panic_hooks", since = "1.10.0")]
-pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
+pub fn set_hook(hook: Box<dyn Fn(&PanicInfo) + 'static + Sync + Send>) {
     if thread::panicking() {
         panic!("cannot modify the panic hook from a panicking thread");
     }
@@ -149,7 +149,7 @@ pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
 /// panic!("Normal panic");
 /// ```
 #[stable(feature = "panic_hooks", since = "1.10.0")]
-pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
+pub fn take_hook() -> Box<dyn Fn(&PanicInfo) + 'static + Sync + Send> {
     if thread::panicking() {
         panic!("cannot modify the panic hook from a panicking thread");
     }
@@ -197,7 +197,7 @@ fn default_hook(info: &PanicInfo) {
     let thread = thread_info::current_thread();
     let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 
-    let write = |err: &mut ::io::Write| {
+    let write = |err: &mut dyn (::io::Write)| {
         let _ = writeln!(err, "thread '{}' panicked at '{}', {}",
                          name, msg, location);
 
@@ -248,7 +248,7 @@ pub fn update_panic_count(amt: isize) -> usize {
 pub use realstd::rt::update_panic_count;
 
 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
-pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
+pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
     #[allow(unions_with_drop_fields)]
     union Data<F, R> {
         f: F,
@@ -369,12 +369,12 @@ fn continue_panic_fmt(info: &PanicInfo) -> ! {
     }
 
     unsafe impl<'a> BoxMeUp for PanicPayload<'a> {
-        fn box_me_up(&mut self) -> *mut (Any + Send) {
+        fn box_me_up(&mut self) -> *mut (dyn Any + Send) {
             let contents = mem::replace(self.fill(), String::new());
             Box::into_raw(Box::new(contents))
         }
 
-        fn get(&mut self) -> &(Any + Send) {
+        fn get(&mut self) -> &(dyn Any + Send) {
             self.fill()
         }
     }
@@ -419,15 +419,15 @@ pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u3
     }
 
     unsafe impl<A: Send + 'static> BoxMeUp for PanicPayload<A> {
-        fn box_me_up(&mut self) -> *mut (Any + Send) {
+        fn box_me_up(&mut self) -> *mut (dyn Any + Send) {
             let data = match self.inner.take() {
-                Some(a) => Box::new(a) as Box<Any + Send>,
+                Some(a) => Box::new(a) as Box<dyn Any + Send>,
                 None => Box::new(()),
             };
             Box::into_raw(data)
         }
 
-        fn get(&mut self) -> &(Any + Send) {
+        fn get(&mut self) -> &(dyn Any + Send) {
             match self.inner {
                 Some(ref a) => a,
                 None => &(),
@@ -441,7 +441,7 @@ pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u3
 /// Executes the primary logic for a panic, including checking for recursive
 /// panics, panic hooks, and finally dispatching to the panic runtime to either
 /// abort or unwind.
-fn rust_panic_with_hook(payload: &mut BoxMeUp,
+fn rust_panic_with_hook(payload: &mut dyn BoxMeUp,
                         message: Option<&fmt::Arguments>,
                         file_line_col: &(&str, u32, u32)) -> ! {
     let (file, line, col) = *file_line_col;
@@ -496,17 +496,17 @@ fn rust_panic_with_hook(payload: &mut BoxMeUp,
 }
 
 /// Shim around rust_panic. Called by resume_unwind.
-pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
+pub fn update_count_then_panic(msg: Box<dyn Any + Send>) -> ! {
     update_panic_count(1);
 
-    struct RewrapBox(Box<Any + Send>);
+    struct RewrapBox(Box<dyn Any + Send>);
 
     unsafe impl BoxMeUp for RewrapBox {
-        fn box_me_up(&mut self) -> *mut (Any + Send) {
+        fn box_me_up(&mut self) -> *mut (dyn Any + Send) {
             Box::into_raw(mem::replace(&mut self.0, Box::new(())))
         }
 
-        fn get(&mut self) -> &(Any + Send) {
+        fn get(&mut self) -> &(dyn Any + Send) {
             &*self.0
         }
     }
@@ -517,9 +517,9 @@ pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
 /// A private no-mangle function on which to slap yer breakpoints.
 #[no_mangle]
 #[allow(private_no_mangle_fns)] // yes we get it, but we like breakpoints
-pub fn rust_panic(mut msg: &mut BoxMeUp) -> ! {
+pub fn rust_panic(mut msg: &mut dyn BoxMeUp) -> ! {
     let code = unsafe {
-        let obj = &mut msg as *mut &mut BoxMeUp;
+        let obj = &mut msg as *mut &mut dyn BoxMeUp;
         __rust_start_panic(obj as usize)
     };
     rtabort!("failed to initiate panic, error {}", code)
diff --git a/src/libstd/process.rs b/src/libstd/process.rs
index 00051d4487a..39692836866 100644
--- a/src/libstd/process.rs
+++ b/src/libstd/process.rs
@@ -813,13 +813,13 @@ impl fmt::Debug for Output {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
 
         let stdout_utf8 = str::from_utf8(&self.stdout);
-        let stdout_debug: &fmt::Debug = match stdout_utf8 {
+        let stdout_debug: &dyn fmt::Debug = match stdout_utf8 {
             Ok(ref str) => str,
             Err(_) => &self.stdout
         };
 
         let stderr_utf8 = str::from_utf8(&self.stderr);
-        let stderr_debug: &fmt::Debug = match stderr_utf8 {
+        let stderr_debug: &dyn fmt::Debug = match stderr_utf8 {
             Ok(ref str) => str,
             Err(_) => &self.stderr
         };
diff --git a/src/libstd/rt.rs b/src/libstd/rt.rs
index 8f945470b7e..9e957bd87d7 100644
--- a/src/libstd/rt.rs
+++ b/src/libstd/rt.rs
@@ -29,7 +29,7 @@ pub use panicking::{begin_panic, begin_panic_fmt, update_panic_count};
 // To reduce the generated code of the new `lang_start`, this function is doing
 // the real work.
 #[cfg(not(test))]
-fn lang_start_internal(main: &(Fn() -> i32 + Sync + ::panic::RefUnwindSafe),
+fn lang_start_internal(main: &(dyn Fn() -> i32 + Sync + ::panic::RefUnwindSafe),
                        argc: isize, argv: *const *const u8) -> isize {
     use panic;
     use sys;
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index cbda5afadcd..02a96b01cca 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/src/libstd/sync/mpsc/mod.rs
@@ -1638,7 +1638,7 @@ impl<T: Send> error::Error for SendError<T> {
         "sending on a closed channel"
     }
 
-    fn cause(&self) -> Option<&error::Error> {
+    fn cause(&self) -> Option<&dyn error::Error> {
         None
     }
 }
@@ -1681,7 +1681,7 @@ impl<T: Send> error::Error for TrySendError<T> {
         }
     }
 
-    fn cause(&self) -> Option<&error::Error> {
+    fn cause(&self) -> Option<&dyn error::Error> {
         None
     }
 }
@@ -1709,7 +1709,7 @@ impl error::Error for RecvError {
         "receiving on a closed channel"
     }
 
-    fn cause(&self) -> Option<&error::Error> {
+    fn cause(&self) -> Option<&dyn error::Error> {
         None
     }
 }
@@ -1742,7 +1742,7 @@ impl error::Error for TryRecvError {
         }
     }
 
-    fn cause(&self) -> Option<&error::Error> {
+    fn cause(&self) -> Option<&dyn error::Error> {
         None
     }
 }
@@ -1783,7 +1783,7 @@ impl error::Error for RecvTimeoutError {
         }
     }
 
-    fn cause(&self) -> Option<&error::Error> {
+    fn cause(&self) -> Option<&dyn error::Error> {
         None
     }
 }
diff --git a/src/libstd/sync/mpsc/select.rs b/src/libstd/sync/mpsc/select.rs
index 9310dad9172..a7a284cfb79 100644
--- a/src/libstd/sync/mpsc/select.rs
+++ b/src/libstd/sync/mpsc/select.rs
@@ -93,7 +93,7 @@ pub struct Handle<'rx, T:Send+'rx> {
     next: *mut Handle<'static, ()>,
     prev: *mut Handle<'static, ()>,
     added: bool,
-    packet: &'rx (Packet+'rx),
+    packet: &'rx (dyn Packet+'rx),
 
     // due to our fun transmutes, we be sure to place this at the end. (nothing
     // previous relies on T)
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index 443e2a6980d..10282ecb658 100644
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -309,7 +309,7 @@ impl Once {
     #[cold]
     fn call_inner(&self,
                   ignore_poisoning: bool,
-                  init: &mut FnMut(bool)) {
+                  init: &mut dyn FnMut(bool)) {
         let mut state = self.state.load(Ordering::SeqCst);
 
         'outer: loop {
diff --git a/src/libstd/sys/cloudabi/thread.rs b/src/libstd/sys/cloudabi/thread.rs
index 5d66936b2a4..8cca47efd22 100644
--- a/src/libstd/sys/cloudabi/thread.rs
+++ b/src/libstd/sys/cloudabi/thread.rs
@@ -32,7 +32,7 @@ unsafe impl Send for Thread {}
 unsafe impl Sync for Thread {}
 
 impl Thread {
-    pub unsafe fn new<'a>(stack: usize, p: Box<FnBox() + 'a>) -> io::Result<Thread> {
+    pub unsafe fn new<'a>(stack: usize, p: Box<dyn FnBox() + 'a>) -> io::Result<Thread> {
         let p = box p;
         let mut native: libc::pthread_t = mem::zeroed();
         let mut attr: libc::pthread_attr_t = mem::zeroed();
diff --git a/src/libstd/sys/redox/process.rs b/src/libstd/sys/redox/process.rs
index d0b94e14f54..02bc467541e 100644
--- a/src/libstd/sys/redox/process.rs
+++ b/src/libstd/sys/redox/process.rs
@@ -51,7 +51,7 @@ pub struct Command {
     uid: Option<u32>,
     gid: Option<u32>,
     saw_nul: bool,
-    closures: Vec<Box<FnMut() -> io::Result<()> + Send + Sync>>,
+    closures: Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>>,
     stdin: Option<Stdio>,
     stdout: Option<Stdio>,
     stderr: Option<Stdio>,
@@ -122,7 +122,7 @@ impl Command {
     }
 
     pub fn before_exec(&mut self,
-                       f: Box<FnMut() -> io::Result<()> + Send + Sync>) {
+                       f: Box<dyn FnMut() -> io::Result<()> + Send + Sync>) {
         self.closures.push(f);
     }
 
diff --git a/src/libstd/sys/redox/thread.rs b/src/libstd/sys/redox/thread.rs
index 110d46ca3ab..f4177087d77 100644
--- a/src/libstd/sys/redox/thread.rs
+++ b/src/libstd/sys/redox/thread.rs
@@ -28,7 +28,7 @@ unsafe impl Send for Thread {}
 unsafe impl Sync for Thread {}
 
 impl Thread {
-    pub unsafe fn new<'a>(_stack: usize, p: Box<FnBox() + 'a>) -> io::Result<Thread> {
+    pub unsafe fn new<'a>(_stack: usize, p: Box<dyn FnBox() + 'a>) -> io::Result<Thread> {
         let p = box p;
 
         let id = cvt(syscall::clone(syscall::CLONE_VM | syscall::CLONE_FS | syscall::CLONE_FILES))?;
diff --git a/src/libstd/sys/unix/process/process_common.rs b/src/libstd/sys/unix/process/process_common.rs
index 6396bb3a49e..77f125f3c5b 100644
--- a/src/libstd/sys/unix/process/process_common.rs
+++ b/src/libstd/sys/unix/process/process_common.rs
@@ -52,7 +52,7 @@ pub struct Command {
     uid: Option<uid_t>,
     gid: Option<gid_t>,
     saw_nul: bool,
-    closures: Vec<Box<FnMut() -> io::Result<()> + Send + Sync>>,
+    closures: Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>>,
     stdin: Option<Stdio>,
     stdout: Option<Stdio>,
     stderr: Option<Stdio>,
@@ -155,12 +155,12 @@ impl Command {
         self.gid
     }
 
-    pub fn get_closures(&mut self) -> &mut Vec<Box<FnMut() -> io::Result<()> + Send + Sync>> {
+    pub fn get_closures(&mut self) -> &mut Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>> {
         &mut self.closures
     }
 
     pub fn before_exec(&mut self,
-                       f: Box<FnMut() -> io::Result<()> + Send + Sync>) {
+                       f: Box<dyn FnMut() -> io::Result<()> + Send + Sync>) {
         self.closures.push(f);
     }
 
diff --git a/src/libstd/sys/unix/thread.rs b/src/libstd/sys/unix/thread.rs
index 7fdecc9c0c0..e26306c045d 100644
--- a/src/libstd/sys/unix/thread.rs
+++ b/src/libstd/sys/unix/thread.rs
@@ -49,7 +49,7 @@ unsafe fn pthread_attr_setstacksize(_attr: *mut libc::pthread_attr_t,
 }
 
 impl Thread {
-    pub unsafe fn new<'a>(stack: usize, p: Box<FnBox() + 'a>)
+    pub unsafe fn new<'a>(stack: usize, p: Box<dyn FnBox() + 'a>)
                           -> io::Result<Thread> {
         let p = box p;
         let mut native: libc::pthread_t = mem::zeroed();
diff --git a/src/libstd/sys/wasm/thread.rs b/src/libstd/sys/wasm/thread.rs
index 728e678a2e8..8173a624211 100644
--- a/src/libstd/sys/wasm/thread.rs
+++ b/src/libstd/sys/wasm/thread.rs
@@ -19,7 +19,7 @@ pub struct Thread(Void);
 pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
 
 impl Thread {
-    pub unsafe fn new<'a>(_stack: usize, _p: Box<FnBox() + 'a>)
+    pub unsafe fn new<'a>(_stack: usize, _p: Box<dyn FnBox() + 'a>)
         -> io::Result<Thread>
     {
         unsupported()
diff --git a/src/libstd/sys/windows/thread.rs b/src/libstd/sys/windows/thread.rs
index b6f63303dc2..44ec872b244 100644
--- a/src/libstd/sys/windows/thread.rs
+++ b/src/libstd/sys/windows/thread.rs
@@ -28,7 +28,7 @@ pub struct Thread {
 }
 
 impl Thread {
-    pub unsafe fn new<'a>(stack: usize, p: Box<FnBox() + 'a>)
+    pub unsafe fn new<'a>(stack: usize, p: Box<dyn FnBox() + 'a>)
                           -> io::Result<Thread> {
         let p = box p;
 
diff --git a/src/libstd/sys_common/at_exit_imp.rs b/src/libstd/sys_common/at_exit_imp.rs
index d268d9ad6f9..b28a4d2f8be 100644
--- a/src/libstd/sys_common/at_exit_imp.rs
+++ b/src/libstd/sys_common/at_exit_imp.rs
@@ -17,7 +17,7 @@ use ptr;
 use mem;
 use sys_common::mutex::Mutex;
 
-type Queue = Vec<Box<FnBox()>>;
+type Queue = Vec<Box<dyn FnBox()>>;
 
 // NB these are specifically not types from `std::sync` as they currently rely
 // on poisoning and this module needs to operate at a lower level than requiring
@@ -68,7 +68,7 @@ pub fn cleanup() {
     }
 }
 
-pub fn push(f: Box<FnBox()>) -> bool {
+pub fn push(f: Box<dyn FnBox()>) -> bool {
     unsafe {
         let _guard = LOCK.lock();
         if init() {
diff --git a/src/libstd/sys_common/backtrace.rs b/src/libstd/sys_common/backtrace.rs
index 2db47bd5947..77371782977 100644
--- a/src/libstd/sys_common/backtrace.rs
+++ b/src/libstd/sys_common/backtrace.rs
@@ -49,7 +49,7 @@ pub struct Frame {
 const MAX_NB_FRAMES: usize = 100;
 
 /// Prints the current backtrace.
-pub fn print(w: &mut Write, format: PrintFormat) -> io::Result<()> {
+pub fn print(w: &mut dyn Write, format: PrintFormat) -> io::Result<()> {
     static LOCK: Mutex = Mutex::new();
 
     // Use a lock to prevent mixed output in multithreading context.
@@ -62,7 +62,7 @@ pub fn print(w: &mut Write, format: PrintFormat) -> io::Result<()> {
     }
 }
 
-fn _print(w: &mut Write, format: PrintFormat) -> io::Result<()> {
+fn _print(w: &mut dyn Write, format: PrintFormat) -> io::Result<()> {
     let mut frames = [Frame {
         exact_position: ptr::null(),
         symbol_addr: ptr::null(),
@@ -176,7 +176,7 @@ pub fn log_enabled() -> Option<PrintFormat> {
 ///
 /// These output functions should now be used everywhere to ensure consistency.
 /// You may want to also use `output_fileline`.
-fn output(w: &mut Write, idx: usize, frame: Frame,
+fn output(w: &mut dyn Write, idx: usize, frame: Frame,
               s: Option<&str>, format: PrintFormat) -> io::Result<()> {
     // Remove the `17: 0x0 - <unknown>` line.
     if format == PrintFormat::Short && frame.exact_position == ptr::null() {
@@ -201,7 +201,7 @@ fn output(w: &mut Write, idx: usize, frame: Frame,
 ///
 /// See also `output`.
 #[allow(dead_code)]
-fn output_fileline(w: &mut Write,
+fn output_fileline(w: &mut dyn Write,
                    file: &[u8],
                    line: u32,
                    format: PrintFormat) -> io::Result<()> {
@@ -253,7 +253,7 @@ fn output_fileline(w: &mut Write,
 // Note that this demangler isn't quite as fancy as it could be. We have lots
 // of other information in our symbols like hashes, version, type information,
 // etc. Additionally, this doesn't handle glue symbols at all.
-pub fn demangle(writer: &mut Write, mut s: &str, format: PrintFormat) -> io::Result<()> {
+pub fn demangle(writer: &mut dyn Write, mut s: &str, format: PrintFormat) -> io::Result<()> {
     // During ThinLTO LLVM may import and rename internal symbols, so strip out
     // those endings first as they're one of the last manglings applied to
     // symbol names.
diff --git a/src/libstd/sys_common/poison.rs b/src/libstd/sys_common/poison.rs
index e74c40ae04b..1625efe4a2a 100644
--- a/src/libstd/sys_common/poison.rs
+++ b/src/libstd/sys_common/poison.rs
@@ -251,7 +251,7 @@ impl<T> Error for TryLockError<T> {
         }
     }
 
-    fn cause(&self) -> Option<&Error> {
+    fn cause(&self) -> Option<&dyn Error> {
         match *self {
             TryLockError::Poisoned(ref p) => Some(p),
             _ => None
diff --git a/src/libstd/sys_common/thread.rs b/src/libstd/sys_common/thread.rs
index da6f58ef6bb..86a5e2b8694 100644
--- a/src/libstd/sys_common/thread.rs
+++ b/src/libstd/sys_common/thread.rs
@@ -21,7 +21,7 @@ pub unsafe fn start_thread(main: *mut u8) {
     let _handler = stack_overflow::Handler::new();
 
     // Finally, let's run some code.
-    Box::from_raw(main as *mut Box<FnBox()>)()
+    Box::from_raw(main as *mut Box<dyn FnBox()>)()
 }
 
 pub fn min_stack() -> usize {
diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
index 90f054186d1..f7052e4834a 100644
--- a/src/libstd/thread/mod.rs
+++ b/src/libstd/thread/mod.rs
@@ -1175,7 +1175,7 @@ impl fmt::Debug for Thread {
 ///
 /// [`Result`]: ../../std/result/enum.Result.html
 #[stable(feature = "rust1", since = "1.0.0")]
-pub type Result<T> = ::result::Result<T, Box<Any + Send + 'static>>;
+pub type Result<T> = ::result::Result<T, Box<dyn Any + Send + 'static>>;
 
 // This packet is used to communicate the return value between the child thread
 // and the parent thread. Memory is shared through the `Arc` within and there's
@@ -1438,7 +1438,7 @@ mod tests {
         rx.recv().unwrap();
     }
 
-    fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Box<Fn() + Send>) {
+    fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Box<dyn Fn() + Send>) {
         let (tx, rx) = channel();
 
         let x: Box<_> = box 1;
@@ -1485,7 +1485,7 @@ mod tests {
         // (well, it would if the constant were 8000+ - I lowered it to be more
         // valgrind-friendly. try this at home, instead..!)
         const GENERATIONS: u32 = 16;
-        fn child_no(x: u32) -> Box<Fn() + Send> {
+        fn child_no(x: u32) -> Box<dyn Fn() + Send> {
             return Box::new(move|| {
                 if x < GENERATIONS {
                     thread::spawn(move|| child_no(x+1)());
@@ -1531,10 +1531,10 @@ mod tests {
     #[test]
     fn test_try_panic_message_any() {
         match thread::spawn(move|| {
-            panic!(box 413u16 as Box<Any + Send>);
+            panic!(box 413u16 as Box<dyn Any + Send>);
         }).join() {
             Err(e) => {
-                type T = Box<Any + Send>;
+                type T = Box<dyn Any + Send>;
                 assert!(e.is::<T>());
                 let any = e.downcast::<T>().unwrap();
                 assert!(any.is::<u16>());
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index d241ae1d442..60de94821bb 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -14,8 +14,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
diff --git a/src/libsyntax_ext/lib.rs b/src/libsyntax_ext/lib.rs
index ff76e788b3c..f0d33835cd0 100644
--- a/src/libsyntax_ext/lib.rs
+++ b/src/libsyntax_ext/lib.rs
@@ -10,8 +10,6 @@
 
 //! Syntax extensions in the Rust compiler.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/libsyntax_pos/lib.rs b/src/libsyntax_pos/lib.rs
index cc09a944e4c..61af70af47d 100644
--- a/src/libsyntax_pos/lib.rs
+++ b/src/libsyntax_pos/lib.rs
@@ -14,8 +14,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![deny(bare_trait_objects)]
-
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
diff --git a/src/libterm/lib.rs b/src/libterm/lib.rs
index a012f4e776f..cf92ce27ee5 100644
--- a/src/libterm/lib.rs
+++ b/src/libterm/lib.rs
@@ -66,9 +66,9 @@ pub mod terminfo;
 mod win;
 
 /// Alias for stdout terminals.
-pub type StdoutTerminal = Terminal<Output = Stdout> + Send;
+pub type StdoutTerminal = dyn Terminal<Output = Stdout> + Send;
 /// Alias for stderr terminals.
-pub type StderrTerminal = Terminal<Output = Stderr> + Send;
+pub type StderrTerminal = dyn Terminal<Output = Stderr> + Send;
 
 #[cfg(not(windows))]
 /// Return a Terminal wrapping stdout, or None if a terminal couldn't be
diff --git a/src/libterm/terminfo/mod.rs b/src/libterm/terminfo/mod.rs
index c5e68eed407..51e0fa315f4 100644
--- a/src/libterm/terminfo/mod.rs
+++ b/src/libterm/terminfo/mod.rs
@@ -58,7 +58,7 @@ impl error::Error for Error {
         "failed to create TermInfo"
     }
 
-    fn cause(&self) -> Option<&error::Error> {
+    fn cause(&self) -> Option<&dyn error::Error> {
         use self::Error::*;
         match self {
             &IoError(ref e) => Some(e),
diff --git a/src/libterm/terminfo/parser/compiled.rs b/src/libterm/terminfo/parser/compiled.rs
index 0cdea64db8b..d5e5df54733 100644
--- a/src/libterm/terminfo/parser/compiled.rs
+++ b/src/libterm/terminfo/parser/compiled.rs
@@ -164,7 +164,7 @@ pub static stringnames: &'static[&'static str] = &[ "cbt", "_", "cr", "csr", "tb
     "OTG3", "OTG1", "OTG4", "OTGR", "OTGL", "OTGU", "OTGD", "OTGH", "OTGV", "OTGC", "meml", "memu",
     "box1"];
 
-fn read_le_u16(r: &mut io::Read) -> io::Result<u16> {
+fn read_le_u16(r: &mut dyn io::Read) -> io::Result<u16> {
     let mut b = [0; 2];
     let mut amt = 0;
     while amt < b.len() {
@@ -176,7 +176,7 @@ fn read_le_u16(r: &mut io::Read) -> io::Result<u16> {
     Ok((b[0] as u16) | ((b[1] as u16) << 8))
 }
 
-fn read_byte(r: &mut io::Read) -> io::Result<u8> {
+fn read_byte(r: &mut dyn io::Read) -> io::Result<u8> {
     match r.bytes().next() {
         Some(s) => s,
         None => Err(io::Error::new(io::ErrorKind::Other, "end of file")),
@@ -185,7 +185,7 @@ fn read_byte(r: &mut io::Read) -> io::Result<u8> {
 
 /// Parse a compiled terminfo entry, using long capability names if `longnames`
 /// is true
-pub fn parse(file: &mut io::Read, longnames: bool) -> Result<TermInfo, String> {
+pub fn parse(file: &mut dyn io::Read, longnames: bool) -> Result<TermInfo, String> {
     macro_rules! t( ($e:expr) => (
         match $e {
             Ok(e) => e,
diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs
index 6b547dff912..76206e2c10d 100644
--- a/src/libtest/lib.rs
+++ b/src/libtest/lib.rs
@@ -27,8 +27,6 @@
 // this crate, which relies on this attribute (rather than the value of `--crate-name` passed by
 // cargo) to detect this crate.
 
-#![deny(bare_trait_objects)]
-
 #![crate_name = "test"]
 #![unstable(feature = "test", issue = "27812")]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
diff --git a/src/libunwind/lib.rs b/src/libunwind/lib.rs
index ea5eee3cc7d..2b3c19c067e 100644
--- a/src/libunwind/lib.rs
+++ b/src/libunwind/lib.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(bare_trait_objects)]
-
 #![no_std]
 #![unstable(feature = "panic_unwind", issue = "32837")]
 
diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index e9b853722c2..d77261f4959 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -416,7 +416,7 @@ impl TestProps {
     }
 }
 
-fn iter_header(testfile: &Path, cfg: Option<&str>, it: &mut FnMut(&str)) {
+fn iter_header(testfile: &Path, cfg: Option<&str>, it: &mut dyn FnMut(&str)) {
     if testfile.is_dir() {
         return;
     }
diff --git a/src/tools/compiletest/src/read2.rs b/src/tools/compiletest/src/read2.rs
index 5bf898f5f1b..f056a041c13 100644
--- a/src/tools/compiletest/src/read2.rs
+++ b/src/tools/compiletest/src/read2.rs
@@ -21,7 +21,7 @@ mod imp {
     pub fn read2(
         out_pipe: ChildStdout,
         err_pipe: ChildStderr,
-        data: &mut FnMut(bool, &mut Vec<u8>, bool),
+        data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
     ) -> io::Result<()> {
         let mut buffer = Vec::new();
         out_pipe.read_to_end(&mut buffer)?;
@@ -45,7 +45,7 @@ mod imp {
     pub fn read2(
         mut out_pipe: ChildStdout,
         mut err_pipe: ChildStderr,
-        data: &mut FnMut(bool, &mut Vec<u8>, bool),
+        data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
     ) -> io::Result<()> {
         unsafe {
             libc::fcntl(out_pipe.as_raw_fd(), libc::F_SETFL, libc::O_NONBLOCK);
@@ -133,7 +133,7 @@ mod imp {
     pub fn read2(
         out_pipe: ChildStdout,
         err_pipe: ChildStderr,
-        data: &mut FnMut(bool, &mut Vec<u8>, bool),
+        data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
     ) -> io::Result<()> {
         let mut out = Vec::new();
         let mut err = Vec::new();
diff --git a/src/tools/error_index_generator/main.rs b/src/tools/error_index_generator/main.rs
index ade7ae0a4ae..e72f90554d3 100644
--- a/src/tools/error_index_generator/main.rs
+++ b/src/tools/error_index_generator/main.rs
@@ -44,18 +44,18 @@ impl OutputFormat {
 }
 
 trait Formatter {
-    fn header(&self, output: &mut Write) -> Result<(), Box<Error>>;
-    fn title(&self, output: &mut Write) -> Result<(), Box<Error>>;
-    fn error_code_block(&self, output: &mut Write, info: &ErrorMetadata,
-                        err_code: &str) -> Result<(), Box<Error>>;
-    fn footer(&self, output: &mut Write) -> Result<(), Box<Error>>;
+    fn header(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>>;
+    fn title(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>>;
+    fn error_code_block(&self, output: &mut dyn Write, info: &ErrorMetadata,
+                        err_code: &str) -> Result<(), Box<dyn Error>>;
+    fn footer(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>>;
 }
 
 struct HTMLFormatter;
 struct MarkdownFormatter;
 
 impl Formatter for HTMLFormatter {
-    fn header(&self, output: &mut Write) -> Result<(), Box<Error>> {
+    fn header(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>> {
         write!(output, r##"<!DOCTYPE html>
 <html>
 <head>
@@ -75,13 +75,13 @@ impl Formatter for HTMLFormatter {
         Ok(())
     }
 
-    fn title(&self, output: &mut Write) -> Result<(), Box<Error>> {
+    fn title(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>> {
         write!(output, "<h1>Rust Compiler Error Index</h1>\n")?;
         Ok(())
     }
 
-    fn error_code_block(&self, output: &mut Write, info: &ErrorMetadata,
-                        err_code: &str) -> Result<(), Box<Error>> {
+    fn error_code_block(&self, output: &mut dyn Write, info: &ErrorMetadata,
+                        err_code: &str) -> Result<(), Box<dyn Error>> {
         // Enclose each error in a div so they can be shown/hidden en masse.
         let desc_desc = match info.description {
             Some(_) => "error-described",
@@ -108,7 +108,7 @@ impl Formatter for HTMLFormatter {
         Ok(())
     }
 
-    fn footer(&self, output: &mut Write) -> Result<(), Box<Error>> {
+    fn footer(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>> {
         write!(output, r##"<script>
 function onEach(arr, func) {{
     if (arr && arr.length > 0 && func) {{
@@ -174,17 +174,17 @@ onEach(document.getElementsByClassName('rust-example-rendered'), function(e) {{
 
 impl Formatter for MarkdownFormatter {
     #[allow(unused_variables)]
-    fn header(&self, output: &mut Write) -> Result<(), Box<Error>> {
+    fn header(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>> {
         Ok(())
     }
 
-    fn title(&self, output: &mut Write) -> Result<(), Box<Error>> {
+    fn title(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>> {
         write!(output, "# Rust Compiler Error Index\n")?;
         Ok(())
     }
 
-    fn error_code_block(&self, output: &mut Write, info: &ErrorMetadata,
-                        err_code: &str) -> Result<(), Box<Error>> {
+    fn error_code_block(&self, output: &mut dyn Write, info: &ErrorMetadata,
+                        err_code: &str) -> Result<(), Box<dyn Error>> {
         Ok(match info.description {
             Some(ref desc) => write!(output, "## {}\n{}\n", err_code, desc)?,
             None => (),
@@ -192,13 +192,13 @@ impl Formatter for MarkdownFormatter {
     }
 
     #[allow(unused_variables)]
-    fn footer(&self, output: &mut Write) -> Result<(), Box<Error>> {
+    fn footer(&self, output: &mut dyn Write) -> Result<(), Box<dyn Error>> {
         Ok(())
     }
 }
 
 /// Load all the metadata files from `metadata_dir` into an in-memory map.
-fn load_all_errors(metadata_dir: &Path) -> Result<ErrorMetadataMap, Box<Error>> {
+fn load_all_errors(metadata_dir: &Path) -> Result<ErrorMetadataMap, Box<dyn Error>> {
     let mut all_errors = BTreeMap::new();
 
     for entry in read_dir(metadata_dir)? {
@@ -219,7 +219,7 @@ fn load_all_errors(metadata_dir: &Path) -> Result<ErrorMetadataMap, Box<Error>>
 
 /// Output an HTML page for the errors in `err_map` to `output_path`.
 fn render_error_page<T: Formatter>(err_map: &ErrorMetadataMap, output_path: &Path,
-                                   formatter: T) -> Result<(), Box<Error>> {
+                                   formatter: T) -> Result<(), Box<dyn Error>> {
     let mut output_file = File::create(output_path)?;
 
     formatter.header(&mut output_file)?;
@@ -232,7 +232,7 @@ fn render_error_page<T: Formatter>(err_map: &ErrorMetadataMap, output_path: &Pat
     formatter.footer(&mut output_file)
 }
 
-fn main_with_result(format: OutputFormat, dst: &Path) -> Result<(), Box<Error>> {
+fn main_with_result(format: OutputFormat, dst: &Path) -> Result<(), Box<dyn Error>> {
     let build_arch = env::var("CFG_BUILD")?;
     let metadata_dir = get_metadata_dir(&build_arch);
     let err_map = load_all_errors(&metadata_dir)?;
diff --git a/src/tools/remote-test-client/src/main.rs b/src/tools/remote-test-client/src/main.rs
index 2f5275bb5be..011bf551140 100644
--- a/src/tools/remote-test-client/src/main.rs
+++ b/src/tools/remote-test-client/src/main.rs
@@ -177,7 +177,7 @@ fn start_qemu_emulator(target: &str,
         _ => panic!("cannot start emulator for: {}"< target),
     }
 
-    fn add_files(w: &mut Write, root: &Path, cur: &Path) {
+    fn add_files(w: &mut dyn Write, root: &Path, cur: &Path) {
         for entry in t!(cur.read_dir()) {
             let entry = t!(entry);
             let path = entry.path();
@@ -297,7 +297,7 @@ fn run(files: String, args: Vec<String>) {
     }
 }
 
-fn send(path: &Path, dst: &mut Write) {
+fn send(path: &Path, dst: &mut dyn Write) {
     t!(dst.write_all(path.file_name().unwrap().to_str().unwrap().as_bytes()));
     t!(dst.write_all(&[0]));
     let mut file = t!(File::open(&path));
diff --git a/src/tools/remote-test-server/src/main.rs b/src/tools/remote-test-server/src/main.rs
index ae13acd58bb..5116f6662ff 100644
--- a/src/tools/remote-test-server/src/main.rs
+++ b/src/tools/remote-test-server/src/main.rs
@@ -270,7 +270,7 @@ fn recv<B: BufRead>(dir: &Path, io: &mut B) -> PathBuf {
     return dst
 }
 
-fn my_copy(src: &mut Read, which: u8, dst: &Mutex<Write>) {
+fn my_copy(src: &mut dyn Read, which: u8, dst: &Mutex<dyn Write>) {
     let mut b = [0; 1024];
     loop {
         let n = t!(src.read(&mut b));
@@ -290,7 +290,7 @@ fn my_copy(src: &mut Read, which: u8, dst: &Mutex<Write>) {
     }
 }
 
-fn read_u32(r: &mut Read) -> u32 {
+fn read_u32(r: &mut dyn Read) -> u32 {
     let mut len = [0; 4];
     t!(r.read_exact(&mut len));
     ((len[0] as u32) << 24) |
diff --git a/src/tools/tidy/src/features.rs b/src/tools/tidy/src/features.rs
index c9bc1b9d849..f68ba0b095b 100644
--- a/src/tools/tidy/src/features.rs
+++ b/src/tools/tidy/src/features.rs
@@ -334,7 +334,7 @@ fn get_and_check_lib_features(base_src_path: &Path,
 }
 
 fn map_lib_features(base_src_path: &Path,
-                    mf: &mut FnMut(Result<(&str, Feature), &str>, &Path, usize)) {
+                    mf: &mut dyn FnMut(Result<(&str, Feature), &str>, &Path, usize)) {
     let mut contents = String::new();
     super::walk(base_src_path,
                 &mut |path| super::filter_dirs(path) || path.ends_with("src/test"),
diff --git a/src/tools/tidy/src/lib.rs b/src/tools/tidy/src/lib.rs
index 46217a42009..bb041b39785 100644
--- a/src/tools/tidy/src/lib.rs
+++ b/src/tools/tidy/src/lib.rs
@@ -82,13 +82,13 @@ fn filter_dirs(path: &Path) -> bool {
     skip.iter().any(|p| path.ends_with(p))
 }
 
-fn walk_many(paths: &[&Path], skip: &mut FnMut(&Path) -> bool, f: &mut FnMut(&Path)) {
+fn walk_many(paths: &[&Path], skip: &mut dyn FnMut(&Path) -> bool, f: &mut dyn FnMut(&Path)) {
     for path in paths {
         walk(path, skip, f);
     }
 }
 
-fn walk(path: &Path, skip: &mut FnMut(&Path) -> bool, f: &mut FnMut(&Path)) {
+fn walk(path: &Path, skip: &mut dyn FnMut(&Path) -> bool, f: &mut dyn FnMut(&Path)) {
     for entry in t!(fs::read_dir(path), path) {
         let entry = t!(entry);
         let kind = t!(entry.file_type());