Auto merge of #69293 - Dylan-DPC:rollup-imcbvgo, r=Dylan-DPC

Rollup of 5 pull requests

Successful merges:

 - #68863 (ci: switch macOS builders to 10.15)
 - #69142 (Add shared script for linkchecking books.)
 - #69248 (Don't eliminate frame pointers on thumb targets)
 - #69280 (Remove special case for `simd_shuffle` arg promotion)
 - #69284 (Reword OpenOptions::{create, create_new} doc.)

Failed merges:

r? @ghost

18 files changed, 164 insertions, 73 deletions

diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index c680d124f1f..f939f79e4f4 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1051,10 +1051,10 @@ impl Step for Compiletest {
         cmd.arg("--docck-python").arg(builder.python());
 
         if builder.config.build.ends_with("apple-darwin") {
-            // Force /usr/bin/python on macOS for LLDB tests because we're loading the
+            // Force /usr/bin/python3 on macOS for LLDB tests because we're loading the
             // LLDB plugin's compiled module which only works with the system python
             // (namely not Homebrew-installed python)
-            cmd.arg("--lldb-python").arg("/usr/bin/python");
+            cmd.arg("--lldb-python").arg("/usr/bin/python3");
         } else {
             cmd.arg("--lldb-python").arg(builder.python());
         }
diff --git a/src/ci/azure-pipelines/auto.yml b/src/ci/azure-pipelines/auto.yml
index 79a49fc48be..74b7469ea27 100644
--- a/src/ci/azure-pipelines/auto.yml
+++ b/src/ci/azure-pipelines/auto.yml
@@ -63,7 +63,7 @@ jobs:
 - job: macOS
   timeoutInMinutes: 600
   pool:
-    vmImage: macos-10.13
+    vmImage: macos-10.15
   steps:
   - template: steps/run.yml
   strategy:
diff --git a/src/ci/azure-pipelines/steps/run.yml b/src/ci/azure-pipelines/steps/run.yml
index c39f75aba89..ee9425aa1c5 100644
--- a/src/ci/azure-pipelines/steps/run.yml
+++ b/src/ci/azure-pipelines/steps/run.yml
@@ -51,10 +51,6 @@ steps:
   displayName: Install clang
   condition: and(succeeded(), not(variables.SKIP_JOB))
 
-- bash: src/ci/scripts/switch-xcode.sh
-  displayName: Switch to Xcode 9.3
-  condition: and(succeeded(), not(variables.SKIP_JOB))
-
 - bash: src/ci/scripts/install-wix.sh
   displayName: Install wix
   condition: and(succeeded(), not(variables.SKIP_JOB))
diff --git a/src/ci/azure-pipelines/try.yml b/src/ci/azure-pipelines/try.yml
index b6177b2cc9b..f8ddf0eb46c 100644
--- a/src/ci/azure-pipelines/try.yml
+++ b/src/ci/azure-pipelines/try.yml
@@ -25,7 +25,7 @@ jobs:
 # - job: macOS
 #   timeoutInMinutes: 600
 #   pool:
-#     vmImage: macos-10.13
+#     vmImage: macos-10.15
 #   steps:
 #   - template: steps/run.yml
 #   strategy:
diff --git a/src/ci/scripts/install-clang.sh b/src/ci/scripts/install-clang.sh
index e16a4814197..c242f5d4562 100755
--- a/src/ci/scripts/install-clang.sh
+++ b/src/ci/scripts/install-clang.sh
@@ -19,9 +19,7 @@ if isMacOS; then
     # native clang is configured to use the correct path, but our custom one
     # doesn't. This sets the SDKROOT environment variable to the SDK so that
     # our own clang can figure out the correct include path on its own.
-    if ! [[ -d "/usr/include" ]]; then
-        ciCommandSetEnv SDKROOT "$(xcrun --sdk macosx --show-sdk-path)"
-    fi
+    ciCommandSetEnv SDKROOT "$(xcrun --sdk macosx --show-sdk-path)"
 
     # Configure `AR` specifically so rustbuild doesn't try to infer it as
     # `clang-ar` by accident.
diff --git a/src/ci/scripts/switch-xcode.sh b/src/ci/scripts/switch-xcode.sh
deleted file mode 100755
index 2cbb2ddbc70..00000000000
--- a/src/ci/scripts/switch-xcode.sh
+++ /dev/null
@@ -1,13 +0,0 @@
-#!/bin/bash
-# Switch to XCode 9.3 on OSX since it seems to be the last version that supports
-# i686-apple-darwin. We'll eventually want to upgrade this and it will probably
-# force us to drop i686-apple-darwin, but let's keep the wheels turning for now.
-
-set -euo pipefail
-IFS=$'\n\t'
-
-source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
-
-if isMacOS; then
-    sudo xcode-select --switch /Applications/Xcode_9.3.app
-fi
diff --git a/src/librustc_mir/const_eval/eval_queries.rs b/src/librustc_mir/const_eval/eval_queries.rs
index 4d5464f774f..1cec5d30e9b 100644
--- a/src/librustc_mir/const_eval/eval_queries.rs
+++ b/src/librustc_mir/const_eval/eval_queries.rs
@@ -72,8 +72,8 @@ fn eval_body_using_ecx<'mir, 'tcx>(
     Ok(ret)
 }
 
-/// The `InterpCx` is only meant to be used to do field and index projections into constants for
-/// `simd_shuffle` and const patterns in match arms.
+/// The `InterpCx` is only meant to be used to do field and index projections into promoteds
+/// and const patterns in match arms.
 ///
 /// The function containing the `match` that is currently being analyzed may have generic bounds
 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
diff --git a/src/librustc_mir/transform/promote_consts.rs b/src/librustc_mir/transform/promote_consts.rs
index a5d59860c3d..a11ee57f465 100644
--- a/src/librustc_mir/transform/promote_consts.rs
+++ b/src/librustc_mir/transform/promote_consts.rs
@@ -24,7 +24,6 @@ use rustc_span::{Span, DUMMY_SP};
 use syntax::ast::LitKind;
 
 use rustc_index::vec::{Idx, IndexVec};
-use rustc_target::spec::abi::Abi;
 
 use std::cell::Cell;
 use std::{cmp, iter, mem, usize};
@@ -106,11 +105,10 @@ pub enum Candidate {
     /// Promotion of the `x` in `[x; 32]`.
     Repeat(Location),
 
-    /// Currently applied to function calls where the callee has the unstable
-    /// `#[rustc_args_required_const]` attribute as well as the SIMD shuffle
-    /// intrinsic. The intrinsic requires the arguments are indeed constant and
-    /// the attribute currently provides the semantic requirement that arguments
-    /// must be constant.
+    /// Function calls where the callee has the unstable
+    /// `#[rustc_args_required_const]` attribute. The attribute requires that
+    /// the arguments be constant, usually because they are encoded as an
+    /// immediate operand in a platform intrinsic.
     Argument { bb: BasicBlock, index: usize },
 }
 
@@ -218,17 +216,6 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
 
         if let TerminatorKind::Call { ref func, .. } = *kind {
             if let ty::FnDef(def_id, _) = func.ty(self.body, self.tcx).kind {
-                let fn_sig = self.tcx.fn_sig(def_id);
-                if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = fn_sig.abi() {
-                    let name = self.tcx.item_name(def_id);
-                    // FIXME(eddyb) use `#[rustc_args_required_const(2)]` for shuffles.
-                    if name.as_str().starts_with("simd_shuffle") {
-                        self.candidates.push(Candidate::Argument { bb: location.block, index: 2 });
-
-                        return; // Don't double count `simd_shuffle` candidates
-                    }
-                }
-
                 if let Some(constant_args) = args_required_const(self.tcx, def_id) {
                     for index in constant_args {
                         self.candidates.push(Candidate::Argument { bb: location.block, index });
@@ -730,8 +717,7 @@ pub fn validate_candidates(
         .filter(|&candidate| {
             validator.explicit = candidate.forces_explicit_promotion();
 
-            // FIXME(eddyb) also emit the errors for shuffle indices
-            // and `#[rustc_args_required_const]` arguments here.
+            // FIXME(eddyb) also emit the errors for `#[rustc_args_required_const]` arguments here.
 
             let is_promotable = validator.validate_candidate(candidate).is_ok();
             match candidate {
diff --git a/src/librustc_target/spec/thumb_base.rs b/src/librustc_target/spec/thumb_base.rs
index 204f4723b70..99ab996be95 100644
--- a/src/librustc_target/spec/thumb_base.rs
+++ b/src/librustc_target/spec/thumb_base.rs
@@ -50,6 +50,9 @@ pub fn opts() -> TargetOptions {
         // until we figure a way to add the pretty printers without requiring a volatile load cf.
         // rust-lang/rust#44993.
         emit_debug_gdb_scripts: false,
+        // LLVM is eager to trash the link register when calling `noreturn` functions, which
+        // breaks debugging. Preserve LR by default to prevent that from happening.
+        eliminate_frame_pointer: false,
         ..Default::default()
     }
 }
diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index cff7bbe5ef1..09be3f13050 100644
--- a/src/libstd/fs.rs
+++ b/src/libstd/fs.rs
@@ -844,10 +844,7 @@ impl OpenOptions {
         self
     }
 
-    /// Sets the option for creating a new file.
-    ///
-    /// This option indicates whether a new file will be created if the file
-    /// does not yet already exist.
+    /// Sets the option to create a new file, or open it if it already exists.
     ///
     /// In order for the file to be created, [`write`] or [`append`] access must
     /// be used.
@@ -868,11 +865,10 @@ impl OpenOptions {
         self
     }
 
-    /// Sets the option to always create a new file.
+    /// Sets the option to create a new file, failing if it already exists.
     ///
-    /// This option indicates whether a new file will be created.
-    /// No file is allowed to exist at the target location, also no (dangling)
-    /// symlink.
+    /// No file is allowed to exist at the target location, also no (dangling) symlink. In this
+    /// way, if the call succeeds, the file returned is guaranteed to be new.
     ///
     /// This option is useful because it is atomic. Otherwise between checking
     /// whether a file exists and creating a new one, the file may have been
diff --git a/src/test/incremental/issue-61530.rs b/src/test/incremental/issue-61530.rs
index 06b2957ac62..c9c600efed8 100644
--- a/src/test/incremental/issue-61530.rs
+++ b/src/test/incremental/issue-61530.rs
@@ -1,4 +1,4 @@
-#![feature(repr_simd, platform_intrinsics)]
+#![feature(repr_simd, platform_intrinsics, rustc_attrs)]
 
 // revisions:rpass1 rpass2
 
@@ -6,6 +6,7 @@
 struct I32x2(i32, i32);
 
 extern "platform-intrinsic" {
+    #[rustc_args_required_const(2)]
     fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
 }
 
diff --git a/src/test/ui/issues/issue-38074.rs b/src/test/ui/issues/issue-38074.rs
index 214d6752cef..8f7905b31ec 100644
--- a/src/test/ui/issues/issue-38074.rs
+++ b/src/test/ui/issues/issue-38074.rs
@@ -1,9 +1,10 @@
 // run-pass
 // ignore-emscripten FIXME(#45351)
 
-#![feature(platform_intrinsics, repr_simd)]
+#![feature(platform_intrinsics, repr_simd, rustc_attrs)]
 
 extern "platform-intrinsic" {
+    #[rustc_args_required_const(2)]
     fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
 }
 
diff --git a/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.rs b/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.rs
index 5929d05f4de..c9c9ab879f2 100644
--- a/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.rs
+++ b/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.rs
@@ -42,9 +42,13 @@ extern "platform-intrinsic" {
     fn simd_insert<T, E>(x: T, idx: u32, y: E) -> T;
     fn simd_extract<T, E>(x: T, idx: u32) -> E;
 
+    #[rustc_args_required_const(2)]
     fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
+    #[rustc_args_required_const(2)]
     fn simd_shuffle3<T, U>(x: T, y: T, idx: [u32; 3]) -> U;
+    #[rustc_args_required_const(2)]
     fn simd_shuffle4<T, U>(x: T, y: T, idx: [u32; 4]) -> U;
+    #[rustc_args_required_const(2)]
     fn simd_shuffle8<T, U>(x: T, y: T, idx: [u32; 8]) -> U;
 }
 
diff --git a/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.stderr b/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.stderr
index 78022c0c8bd..29916f85902 100644
--- a/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.stderr
+++ b/src/test/ui/simd-intrinsic/simd-intrinsic-generic-elements.stderr
@@ -1,89 +1,89 @@
 error[E0511]: invalid monomorphization of `simd_insert` intrinsic: expected SIMD input type, found non-SIMD `i32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:55:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:59:9
    |
 LL |         simd_insert(0, 0, 0);
    |         ^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_insert` intrinsic: expected inserted type `i32` (element of input `i32x4`), found `f64`
-  --> $DIR/simd-intrinsic-generic-elements.rs:57:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:61:9
    |
 LL |         simd_insert(x, 0, 1.0);
    |         ^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_extract` intrinsic: expected return type `i32` (element of input `i32x4`), found `f32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:59:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:63:9
    |
 LL |         simd_extract::<_, f32>(x, 0);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle2` intrinsic: expected SIMD input type, found non-SIMD `i32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:62:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:66:9
    |
 LL |         simd_shuffle2::<i32, i32>(0, 0, [0; 2]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle3` intrinsic: expected SIMD input type, found non-SIMD `i32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:64:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:68:9
    |
 LL |         simd_shuffle3::<i32, i32>(0, 0, [0; 3]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle4` intrinsic: expected SIMD input type, found non-SIMD `i32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:66:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:70:9
    |
 LL |         simd_shuffle4::<i32, i32>(0, 0, [0; 4]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle8` intrinsic: expected SIMD input type, found non-SIMD `i32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:68:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:72:9
    |
 LL |         simd_shuffle8::<i32, i32>(0, 0, [0; 8]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle2` intrinsic: expected return element type `i32` (element of input `i32x4`), found `f32x2` with element type `f32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:71:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:75:9
    |
 LL |         simd_shuffle2::<_, f32x2>(x, x, [0; 2]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle3` intrinsic: expected return element type `i32` (element of input `i32x4`), found `f32x3` with element type `f32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:73:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:77:9
    |
 LL |         simd_shuffle3::<_, f32x3>(x, x, [0; 3]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle4` intrinsic: expected return element type `i32` (element of input `i32x4`), found `f32x4` with element type `f32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:75:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:79:9
    |
 LL |         simd_shuffle4::<_, f32x4>(x, x, [0; 4]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle8` intrinsic: expected return element type `i32` (element of input `i32x4`), found `f32x8` with element type `f32`
-  --> $DIR/simd-intrinsic-generic-elements.rs:77:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:81:9
    |
 LL |         simd_shuffle8::<_, f32x8>(x, x, [0; 8]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle2` intrinsic: expected return type of length 2, found `i32x8` with length 8
-  --> $DIR/simd-intrinsic-generic-elements.rs:80:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:84:9
    |
 LL |         simd_shuffle2::<_, i32x8>(x, x, [0; 2]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle3` intrinsic: expected return type of length 3, found `i32x4` with length 4
-  --> $DIR/simd-intrinsic-generic-elements.rs:82:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:86:9
    |
 LL |         simd_shuffle3::<_, i32x4>(x, x, [0; 3]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle4` intrinsic: expected return type of length 4, found `i32x3` with length 3
-  --> $DIR/simd-intrinsic-generic-elements.rs:84:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:88:9
    |
 LL |         simd_shuffle4::<_, i32x3>(x, x, [0; 4]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_shuffle8` intrinsic: expected return type of length 8, found `i32x2` with length 2
-  --> $DIR/simd-intrinsic-generic-elements.rs:86:9
+  --> $DIR/simd-intrinsic-generic-elements.rs:90:9
    |
 LL |         simd_shuffle8::<_, i32x2>(x, x, [0; 8]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557-ice.rs b/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557-ice.rs
index 4c09ae25c5f..b03b0ef5089 100644
--- a/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557-ice.rs
+++ b/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557-ice.rs
@@ -3,9 +3,10 @@
 //
 // run-pass
 // compile-flags: -Zmir-opt-level=3
-#![feature(platform_intrinsics, repr_simd)]
+#![feature(platform_intrinsics, repr_simd, rustc_attrs)]
 
 extern "platform-intrinsic" {
+    #[rustc_args_required_const(2)]
     fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
 }
 
diff --git a/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557.rs b/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557.rs
index 7a0d955686b..2741dc13336 100644
--- a/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557.rs
+++ b/src/test/ui/simd-intrinsic/simd-intrinsic-inlining-issue67557.rs
@@ -3,9 +3,10 @@
 //
 // run-pass
 // compile-flags: -Zmir-opt-level=3
-#![feature(platform_intrinsics, repr_simd)]
+#![feature(platform_intrinsics, repr_simd, rustc_attrs)]
 
 extern "platform-intrinsic" {
+    #[rustc_args_required_const(2)]
     fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
 }
 
diff --git a/src/test/ui/simd/simd-intrinsic-generic-elements.rs b/src/test/ui/simd/simd-intrinsic-generic-elements.rs
index ea3d4b18944..abff59fea78 100644
--- a/src/test/ui/simd/simd-intrinsic-generic-elements.rs
+++ b/src/test/ui/simd/simd-intrinsic-generic-elements.rs
@@ -1,7 +1,7 @@
 // run-pass
 // ignore-emscripten FIXME(#45351) hits an LLVM assert
 
-#![feature(repr_simd, platform_intrinsics)]
+#![feature(repr_simd, platform_intrinsics, rustc_attrs)]
 
 #[repr(simd)]
 #[derive(Copy, Clone, Debug, PartialEq)]
@@ -25,9 +25,13 @@ extern "platform-intrinsic" {
     fn simd_insert<T, E>(x: T, idx: u32, y: E) -> T;
     fn simd_extract<T, E>(x: T, idx: u32) -> E;
 
+    #[rustc_args_required_const(2)]
     fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
+    #[rustc_args_required_const(2)]
     fn simd_shuffle3<T, U>(x: T, y: T, idx: [u32; 3]) -> U;
+    #[rustc_args_required_const(2)]
     fn simd_shuffle4<T, U>(x: T, y: T, idx: [u32; 4]) -> U;
+    #[rustc_args_required_const(2)]
     fn simd_shuffle8<T, U>(x: T, y: T, idx: [u32; 8]) -> U;
 }
 
diff --git a/src/tools/linkchecker/linkcheck.sh b/src/tools/linkchecker/linkcheck.sh
new file mode 100755
index 00000000000..bbccc17e494
--- /dev/null
+++ b/src/tools/linkchecker/linkcheck.sh
@@ -0,0 +1,113 @@
+#!/bin/sh
+#
+# This is a script that can be used in each book's CI to validate links using
+# the same tool as rust-lang/rust.
+#
+# This requires the rust-docs rustup component to be installed in the nightly
+# toolchain.
+#
+# Usage:
+#   ./linkcheck.sh <name-of-book>
+#
+# Options:
+#
+# -i        "Iterative" mode. The script will not clean up after it is done so
+#           you can inspect the result, and re-run more quickly.
+#
+# --all     Check all books. This can help make sure you don't break links
+#           from other books into your book.
+
+set -e
+
+if [ ! -f book.toml ] && [ ! -f src/SUMMARY.md ]
+then
+    echo "Run command in root directory of the book."
+    exit 1
+fi
+
+html_dir="$(rustc +nightly --print sysroot)/share/doc/rust/html"
+
+if [ ! -d "$html_dir" ]
+then
+    echo "HTML docs are missing from sysroot: $html_dir"
+    echo "Make sure the nightly rust-docs rustup component is installed."
+    exit 1
+fi
+
+book_name=""
+# Iterative will avoid cleaning up, so you can quickly run it repeatedly.
+iterative=0
+# If "1", test all books, else only this book.
+all_books=0
+
+while [ "$1" != "" ]
+do
+    case "$1" in
+        -i)
+            iterative=1
+            ;;
+        --all)
+            all_books=1
+            ;;
+        *)
+            if [ -n "$book_name" ]
+            then
+                echo "only one argument allowed"
+                exit 1
+            fi
+            book_name="$1"
+            ;;
+    esac
+    shift
+done
+
+if [ -z "$book_name" ]
+then
+    echo "usage: $0 <name-of-book>"
+    exit 1
+fi
+
+if [ ! -d "$html_dir/$book_name" ]
+then
+    echo "book name \"$book_name\" not found in sysroot \"$html_dir\""
+    exit 1
+fi
+
+if [ "$iterative" = "0" ]
+then
+    echo "Cleaning old directories..."
+    rm -rf linkcheck linkchecker
+fi
+
+if [ ! -e "linkchecker/main.rs" ] || [ "$iterative" = "0" ]
+then
+    echo "Downloading linkchecker source..."
+    mkdir linkchecker
+    curl -o linkchecker/Cargo.toml \
+        https://raw.githubusercontent.com/rust-lang/rust/master/src/tools/linkchecker/Cargo.toml
+    curl -o linkchecker/main.rs \
+        https://raw.githubusercontent.com/rust-lang/rust/master/src/tools/linkchecker/main.rs
+fi
+
+echo "Building book \"$book_name\"..."
+mdbook build
+
+cp -R "$html_dir" linkcheck
+rm -rf "linkcheck/$book_name"
+cp -R book "linkcheck/$book_name"
+
+if [ "$all_books" = "1" ]
+then
+    check_path="linkcheck"
+else
+    check_path="linkcheck/$book_name"
+fi
+echo "Running linkchecker on \"$check_path\"..."
+cargo run --manifest-path=linkchecker/Cargo.toml -- "$check_path"
+
+if [ "$iterative" = "0" ]
+then
+    rm -rf linkcheck linkchecker
+fi
+
+echo "Link check completed successfully!"