Point at original span when emitting unreachable lint

Fixes #64590

When we emit an 'unreachable' lint, we now add a note pointing at the
expression that actually causes the code to be unreachable (e.g.
`return`, `break`, `panic`).

This is especially useful when macros are involved, since a diverging
expression might be hidden inside of a macro invocation.

37 files changed, 328 insertions, 11 deletions

diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs
index 308a3d8ebc2..a1c937b95ba 100644
--- a/src/librustc_typeck/check/_match.rs
+++ b/src/librustc_typeck/check/_match.rs
@@ -43,7 +43,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // If there are no arms, that is a diverging match; a special case.
         if arms.is_empty() {
-            self.diverges.set(self.diverges.get() | Diverges::Always);
+            self.diverges.set(self.diverges.get() | Diverges::Always(expr.span));
             return tcx.types.never;
         }
 
@@ -69,7 +69,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // warnings).
             match all_pats_diverge {
                 Diverges::Maybe => Diverges::Maybe,
-                Diverges::Always | Diverges::WarnedAlways => Diverges::WarnedAlways,
+                Diverges::Always(..) | Diverges::WarnedAlways => Diverges::WarnedAlways,
             }
         }).collect();
 
diff --git a/src/librustc_typeck/check/expr.rs b/src/librustc_typeck/check/expr.rs
index 56bd903040a..3ba453748ff 100644
--- a/src/librustc_typeck/check/expr.rs
+++ b/src/librustc_typeck/check/expr.rs
@@ -170,7 +170,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Any expression that produces a value of type `!` must have diverged
         if ty.is_never() {
-            self.diverges.set(self.diverges.get() | Diverges::Always);
+            self.diverges.set(self.diverges.get() | Diverges::Always(expr.span));
         }
 
         // Record the type, which applies it effects.
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 1197160fa95..0fced373946 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -450,7 +450,10 @@ pub enum Diverges {
 
     /// Definitely known to diverge and therefore
     /// not reach the next sibling or its parent.
-    Always,
+    /// The `Span` points to the expression
+    /// that caused us to diverge
+    /// (e.g. `return`, `break`, etc)
+    Always(Span),
 
     /// Same as `Always` but with a reachability
     /// warning already emitted.
@@ -487,7 +490,7 @@ impl ops::BitOrAssign for Diverges {
 
 impl Diverges {
     fn always(self) -> bool {
-        self >= Diverges::Always
+        self >= Diverges::Always(DUMMY_SP)
     }
 }
 
@@ -2307,17 +2310,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Produces warning on the given node, if the current point in the
     /// function is unreachable, and there hasn't been another warning.
     fn warn_if_unreachable(&self, id: hir::HirId, span: Span, kind: &str) {
-        if self.diverges.get() == Diverges::Always &&
+        // FIXME: Combine these two 'if' expressions into one once
+        // let chains are implemented
+        if let Diverges::Always(orig_span) = self.diverges.get() {
             // If span arose from a desugaring of `if` or `while`, then it is the condition itself,
             // which diverges, that we are about to lint on. This gives suboptimal diagnostics.
             // Instead, stop here so that the `if`- or `while`-expression's block is linted instead.
-            !span.is_desugaring(DesugaringKind::CondTemporary) {
-            self.diverges.set(Diverges::WarnedAlways);
+            if !span.is_desugaring(DesugaringKind::CondTemporary) {
+                self.diverges.set(Diverges::WarnedAlways);
 
-            debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
+                debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
 
-            let msg = format!("unreachable {}", kind);
-            self.tcx().lint_hir(lint::builtin::UNREACHABLE_CODE, id, span, &msg);
+                let msg = format!("unreachable {}", kind);
+                let mut err = self.tcx().struct_span_lint_hir(lint::builtin::UNREACHABLE_CODE,
+                                                              id, span, &msg);
+                err.span_note(orig_span, "any code following this expression is unreachable");
+                err.emit();
+            }
         }
     }
 
diff --git a/src/test/ui/dead-code-ret.stderr b/src/test/ui/dead-code-ret.stderr
index 092a176f443..0ce31ea40dd 100644
--- a/src/test/ui/dead-code-ret.stderr
+++ b/src/test/ui/dead-code-ret.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/dead-code-ret.rs:6:5
+   |
+LL |     return;
+   |     ^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error
diff --git a/src/test/ui/if-ret.stderr b/src/test/ui/if-ret.stderr
index 73402e55a4f..2df8f22944e 100644
--- a/src/test/ui/if-ret.stderr
+++ b/src/test/ui/if-ret.stderr
@@ -5,4 +5,9 @@ LL | fn foo() { if (return) { } }
    |                        ^^^
    |
    = note: `#[warn(unreachable_code)]` on by default
+note: any code following this expression is unreachable
+  --> $DIR/if-ret.rs:6:15
+   |
+LL | fn foo() { if (return) { } }
+   |               ^^^^^^^^
 
diff --git a/src/test/ui/issues/issue-2150.stderr b/src/test/ui/issues/issue-2150.stderr
index 59000f3dd53..623f098d0b3 100644
--- a/src/test/ui/issues/issue-2150.stderr
+++ b/src/test/ui/issues/issue-2150.stderr
@@ -9,6 +9,12 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/issue-2150.rs:7:5
+   |
+LL |     panic!();
+   |     ^^^^^^^^^
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-7246.stderr b/src/test/ui/issues/issue-7246.stderr
index e049295e913..d1b23672dc7 100644
--- a/src/test/ui/issues/issue-7246.stderr
+++ b/src/test/ui/issues/issue-7246.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/issue-7246.rs:6:5
+   |
+LL |     return;
+   |     ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/lint/lint-attr-non-item-node.stderr b/src/test/ui/lint/lint-attr-non-item-node.stderr
index 6eb72c098df..e6c76c24c91 100644
--- a/src/test/ui/lint/lint-attr-non-item-node.stderr
+++ b/src/test/ui/lint/lint-attr-non-item-node.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL |     #[deny(unreachable_code)]
    |            ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/lint-attr-non-item-node.rs:6:9
+   |
+LL |         break;
+   |         ^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/liveness/liveness-unused.stderr b/src/test/ui/liveness/liveness-unused.stderr
index 40a677c08f2..84e9b5bab99 100644
--- a/src/test/ui/liveness/liveness-unused.stderr
+++ b/src/test/ui/liveness/liveness-unused.stderr
@@ -10,6 +10,11 @@ note: lint level defined here
 LL | #![warn(unused)]
    |         ^^^^^^
    = note: `#[warn(unreachable_code)]` implied by `#[warn(unused)]`
+note: any code following this expression is unreachable
+  --> $DIR/liveness-unused.rs:91:9
+   |
+LL |         continue;
+   |         ^^^^^^^^
 
 error: unused variable: `x`
   --> $DIR/liveness-unused.rs:8:7
diff --git a/src/test/ui/match/match-no-arms-unreachable-after.stderr b/src/test/ui/match/match-no-arms-unreachable-after.stderr
index 65dcc6ee465..6c46b2473cc 100644
--- a/src/test/ui/match/match-no-arms-unreachable-after.stderr
+++ b/src/test/ui/match/match-no-arms-unreachable-after.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/match-no-arms-unreachable-after.rs:7:5
+   |
+LL |     match v { }
+   |     ^^^^^^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/never-assign-dead-code.stderr b/src/test/ui/never-assign-dead-code.stderr
index b1b5bf03fe5..436c703e4b6 100644
--- a/src/test/ui/never-assign-dead-code.stderr
+++ b/src/test/ui/never-assign-dead-code.stderr
@@ -10,12 +10,24 @@ note: lint level defined here
 LL | #![warn(unused)]
    |         ^^^^^^
    = note: `#[warn(unreachable_code)]` implied by `#[warn(unused)]`
+note: any code following this expression is unreachable
+  --> $DIR/never-assign-dead-code.rs:9:16
+   |
+LL |     let x: ! = panic!("aah");
+   |                ^^^^^^^^^^^^^
+   = note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 warning: unreachable call
   --> $DIR/never-assign-dead-code.rs:10:5
    |
 LL |     drop(x);
    |     ^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/never-assign-dead-code.rs:10:10
+   |
+LL |     drop(x);
+   |          ^
 
 warning: unused variable: `x`
   --> $DIR/never-assign-dead-code.rs:9:9
diff --git a/src/test/ui/reachable/expr_add.stderr b/src/test/ui/reachable/expr_add.stderr
index 02b29021cb6..47b4e467abe 100644
--- a/src/test/ui/reachable/expr_add.stderr
+++ b/src/test/ui/reachable/expr_add.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_add.rs:17:19
+   |
+LL |     let x = Foo + return;
+   |                   ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/reachable/expr_again.stderr b/src/test/ui/reachable/expr_again.stderr
index bdc3d143ea5..8e246d940fd 100644
--- a/src/test/ui/reachable/expr_again.stderr
+++ b/src/test/ui/reachable/expr_again.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_again.rs:7:9
+   |
+LL |         continue;
+   |         ^^^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error
diff --git a/src/test/ui/reachable/expr_array.stderr b/src/test/ui/reachable/expr_array.stderr
index 18d7ffe74bd..419a332e632 100644
--- a/src/test/ui/reachable/expr_array.stderr
+++ b/src/test/ui/reachable/expr_array.stderr
@@ -9,12 +9,23 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_array.rs:9:26
+   |
+LL |     let x: [usize; 2] = [return, 22];
+   |                          ^^^^^^
 
 error: unreachable expression
   --> $DIR/expr_array.rs:14:25
    |
 LL |     let x: [usize; 2] = [22, return];
    |                         ^^^^^^^^^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_array.rs:14:30
+   |
+LL |     let x: [usize; 2] = [22, return];
+   |                              ^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/reachable/expr_assign.stderr b/src/test/ui/reachable/expr_assign.stderr
index def16d90a74..7388fb4a6b9 100644
--- a/src/test/ui/reachable/expr_assign.stderr
+++ b/src/test/ui/reachable/expr_assign.stderr
@@ -9,18 +9,35 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_assign.rs:10:9
+   |
+LL |     x = return;
+   |         ^^^^^^
 
 error: unreachable expression
   --> $DIR/expr_assign.rs:20:14
    |
 LL |         *p = return;
    |              ^^^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_assign.rs:20:9
+   |
+LL |         *p = return;
+   |         ^^
 
 error: unreachable expression
   --> $DIR/expr_assign.rs:26:15
    |
 LL |     *{return; &mut i} = 22;
    |               ^^^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_assign.rs:26:7
+   |
+LL |     *{return; &mut i} = 22;
+   |       ^^^^^^
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/reachable/expr_block.stderr b/src/test/ui/reachable/expr_block.stderr
index a498502e6cb..03a6139d688 100644
--- a/src/test/ui/reachable/expr_block.stderr
+++ b/src/test/ui/reachable/expr_block.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_block.rs:9:9
+   |
+LL |         return;
+   |         ^^^^^^
 
 error: unreachable statement
   --> $DIR/expr_block.rs:25:9
@@ -16,6 +21,11 @@ error: unreachable statement
 LL |         println!("foo");
    |         ^^^^^^^^^^^^^^^^
    |
+note: any code following this expression is unreachable
+  --> $DIR/expr_block.rs:24:9
+   |
+LL |         return;
+   |         ^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
diff --git a/src/test/ui/reachable/expr_box.stderr b/src/test/ui/reachable/expr_box.stderr
index 63137ce3da1..d0f666d2be4 100644
--- a/src/test/ui/reachable/expr_box.stderr
+++ b/src/test/ui/reachable/expr_box.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_box.rs:6:17
+   |
+LL |     let x = box return;
+   |                 ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/reachable/expr_call.stderr b/src/test/ui/reachable/expr_call.stderr
index f2db17e4dfe..3fcea90e7cd 100644
--- a/src/test/ui/reachable/expr_call.stderr
+++ b/src/test/ui/reachable/expr_call.stderr
@@ -9,12 +9,23 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_call.rs:13:9
+   |
+LL |     foo(return, 22);
+   |         ^^^^^^
 
 error: unreachable call
   --> $DIR/expr_call.rs:18:5
    |
 LL |     bar(return);
    |     ^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_call.rs:18:9
+   |
+LL |     bar(return);
+   |         ^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/reachable/expr_cast.stderr b/src/test/ui/reachable/expr_cast.stderr
index 3086745d28e..d3ce0ca079f 100644
--- a/src/test/ui/reachable/expr_cast.stderr
+++ b/src/test/ui/reachable/expr_cast.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_cast.rs:9:14
+   |
+LL |     let x = {return} as !;
+   |              ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/reachable/expr_if.stderr b/src/test/ui/reachable/expr_if.stderr
index f1690e595e5..03284576086 100644
--- a/src/test/ui/reachable/expr_if.stderr
+++ b/src/test/ui/reachable/expr_if.stderr
@@ -12,6 +12,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_if.rs:7:9
+   |
+LL |     if {return} {
+   |         ^^^^^^
 
 error: unreachable statement
   --> $DIR/expr_if.rs:27:5
@@ -19,6 +24,11 @@ error: unreachable statement
 LL |     println!("But I am.");
    |     ^^^^^^^^^^^^^^^^^^^^^^
    |
+note: any code following this expression is unreachable
+  --> $DIR/expr_if.rs:21:9
+   |
+LL |         return;
+   |         ^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
diff --git a/src/test/ui/reachable/expr_loop.stderr b/src/test/ui/reachable/expr_loop.stderr
index 4d3e06c93a3..a4cf8cfcfd9 100644
--- a/src/test/ui/reachable/expr_loop.stderr
+++ b/src/test/ui/reachable/expr_loop.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_loop.rs:7:12
+   |
+LL |     loop { return; }
+   |            ^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: unreachable statement
@@ -17,6 +22,11 @@ error: unreachable statement
 LL |     println!("I am dead.");
    |     ^^^^^^^^^^^^^^^^^^^^^^^
    |
+note: any code following this expression is unreachable
+  --> $DIR/expr_loop.rs:20:12
+   |
+LL |     loop { return; }
+   |            ^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: unreachable statement
@@ -25,6 +35,11 @@ error: unreachable statement
 LL |     println!("I am dead.");
    |     ^^^^^^^^^^^^^^^^^^^^^^^
    |
+note: any code following this expression is unreachable
+  --> $DIR/expr_loop.rs:31:5
+   |
+LL |     loop { 'middle: loop { loop { break 'middle; } } }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to 3 previous errors
diff --git a/src/test/ui/reachable/expr_match.stderr b/src/test/ui/reachable/expr_match.stderr
index 1aef06aec5b..b846b92dcec 100644
--- a/src/test/ui/reachable/expr_match.stderr
+++ b/src/test/ui/reachable/expr_match.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_match.rs:7:22
+   |
+LL |     match () { () => return }
+   |                      ^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: unreachable statement
@@ -17,6 +22,11 @@ error: unreachable statement
 LL |     println!("I am dead");
    |     ^^^^^^^^^^^^^^^^^^^^^^
    |
+note: any code following this expression is unreachable
+  --> $DIR/expr_match.rs:18:31
+   |
+LL |     match () { () if false => return, () => return }
+   |                               ^^^^^^
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
diff --git a/src/test/ui/reachable/expr_method.stderr b/src/test/ui/reachable/expr_method.stderr
index 947ea0fee88..7ad279c9f48 100644
--- a/src/test/ui/reachable/expr_method.stderr
+++ b/src/test/ui/reachable/expr_method.stderr
@@ -9,12 +9,23 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_method.rs:16:13
+   |
+LL |     Foo.foo(return, 22);
+   |             ^^^^^^
 
 error: unreachable call
   --> $DIR/expr_method.rs:21:9
    |
 LL |     Foo.bar(return);
    |         ^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_method.rs:21:13
+   |
+LL |     Foo.bar(return);
+   |             ^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/reachable/expr_repeat.stderr b/src/test/ui/reachable/expr_repeat.stderr
index 0536cdef721..3ff6be76dae 100644
--- a/src/test/ui/reachable/expr_repeat.stderr
+++ b/src/test/ui/reachable/expr_repeat.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_repeat.rs:9:26
+   |
+LL |     let x: [usize; 2] = [return; 2];
+   |                          ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/reachable/expr_return.stderr b/src/test/ui/reachable/expr_return.stderr
index 3317da58aba..31f7ebe7618 100644
--- a/src/test/ui/reachable/expr_return.stderr
+++ b/src/test/ui/reachable/expr_return.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_return.rs:10:30
+   |
+LL |     let x = {return {return {return;}}};
+   |                              ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/reachable/expr_return_in_macro.rs b/src/test/ui/reachable/expr_return_in_macro.rs
new file mode 100644
index 00000000000..198ede6b141
--- /dev/null
+++ b/src/test/ui/reachable/expr_return_in_macro.rs
@@ -0,0 +1,15 @@
+// Tests that we generate nice error messages
+// when an expression is unreachble due to control
+// flow inside of a macro expansion
+#![deny(unreachable_code)]
+
+macro_rules! early_return {
+    () => {
+        return ()
+    }
+}
+
+fn main() {
+    return early_return!();
+    //~^ ERROR unreachable expression
+}
diff --git a/src/test/ui/reachable/expr_return_in_macro.stderr b/src/test/ui/reachable/expr_return_in_macro.stderr
new file mode 100644
index 00000000000..ff3abb5551f
--- /dev/null
+++ b/src/test/ui/reachable/expr_return_in_macro.stderr
@@ -0,0 +1,22 @@
+error: unreachable expression
+  --> $DIR/expr_return_in_macro.rs:13:5
+   |
+LL |     return early_return!();
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/expr_return_in_macro.rs:4:9
+   |
+LL | #![deny(unreachable_code)]
+   |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_return_in_macro.rs:8:9
+   |
+LL |         return ()
+   |         ^^^^^^^^^
+...
+LL |     return early_return!();
+   |            --------------- in this macro invocation
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/reachable/expr_struct.stderr b/src/test/ui/reachable/expr_struct.stderr
index dcccb7a4db3..d08bcc4f0d1 100644
--- a/src/test/ui/reachable/expr_struct.stderr
+++ b/src/test/ui/reachable/expr_struct.stderr
@@ -9,24 +9,47 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_struct.rs:14:35
+   |
+LL |     let x = Foo { a: 22, b: 33, ..return };
+   |                                   ^^^^^^
 
 error: unreachable expression
   --> $DIR/expr_struct.rs:19:33
    |
 LL |     let x = Foo { a: return, b: 33, ..return };
    |                                 ^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_struct.rs:19:22
+   |
+LL |     let x = Foo { a: return, b: 33, ..return };
+   |                      ^^^^^^
 
 error: unreachable expression
   --> $DIR/expr_struct.rs:24:39
    |
 LL |     let x = Foo { a: 22, b: return, ..return };
    |                                       ^^^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_struct.rs:24:29
+   |
+LL |     let x = Foo { a: 22, b: return, ..return };
+   |                             ^^^^^^
 
 error: unreachable expression
   --> $DIR/expr_struct.rs:29:13
    |
 LL |     let x = Foo { a: 22, b: return };
    |             ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_struct.rs:29:29
+   |
+LL |     let x = Foo { a: 22, b: return };
+   |                             ^^^^^^
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/reachable/expr_tup.stderr b/src/test/ui/reachable/expr_tup.stderr
index 1837031107d..788499533db 100644
--- a/src/test/ui/reachable/expr_tup.stderr
+++ b/src/test/ui/reachable/expr_tup.stderr
@@ -9,12 +9,23 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_tup.rs:9:30
+   |
+LL |     let x: (usize, usize) = (return, 2);
+   |                              ^^^^^^
 
 error: unreachable expression
   --> $DIR/expr_tup.rs:14:29
    |
 LL |     let x: (usize, usize) = (2, return);
    |                             ^^^^^^^^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_tup.rs:14:33
+   |
+LL |     let x: (usize, usize) = (2, return);
+   |                                 ^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/reachable/expr_type.stderr b/src/test/ui/reachable/expr_type.stderr
index f867c891634..15eb735da75 100644
--- a/src/test/ui/reachable/expr_type.stderr
+++ b/src/test/ui/reachable/expr_type.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_type.rs:9:14
+   |
+LL |     let x = {return}: !;
+   |              ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/reachable/expr_unary.stderr b/src/test/ui/reachable/expr_unary.stderr
index 61982289cdc..7f865196166 100644
--- a/src/test/ui/reachable/expr_unary.stderr
+++ b/src/test/ui/reachable/expr_unary.stderr
@@ -15,6 +15,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_unary.rs:8:20
+   |
+LL |     let x: ! = ! { return; };
+   |                    ^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/reachable/expr_while.stderr b/src/test/ui/reachable/expr_while.stderr
index fc528926b4c..b6d6d11ac69 100644
--- a/src/test/ui/reachable/expr_while.stderr
+++ b/src/test/ui/reachable/expr_while.stderr
@@ -13,6 +13,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/expr_while.rs:7:12
+   |
+LL |     while {return} {
+   |            ^^^^^^
 
 error: unreachable block in `while` expression
   --> $DIR/expr_while.rs:22:20
@@ -23,6 +28,12 @@ LL | |
 LL | |         println!("I am dead.");
 LL | |     }
    | |_____^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/expr_while.rs:22:12
+   |
+LL |     while {return} {
+   |            ^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/rfc-2497-if-let-chains/protect-precedences.stderr b/src/test/ui/rfc-2497-if-let-chains/protect-precedences.stderr
index be7ef658411..ca98a394714 100644
--- a/src/test/ui/rfc-2497-if-let-chains/protect-precedences.stderr
+++ b/src/test/ui/rfc-2497-if-let-chains/protect-precedences.stderr
@@ -5,4 +5,9 @@ LL |         if let _ = return true && false {};
    |                                         ^^
    |
    = note: `#[warn(unreachable_code)]` on by default
+note: any code following this expression is unreachable
+  --> $DIR/protect-precedences.rs:13:20
+   |
+LL |         if let _ = return true && false {};
+   |                    ^^^^^^^^^^^^^^^^^^^^
 
diff --git a/src/test/ui/unreachable/unreachable-code.stderr b/src/test/ui/unreachable/unreachable-code.stderr
index 803bb966be8..226f088c63a 100644
--- a/src/test/ui/unreachable/unreachable-code.stderr
+++ b/src/test/ui/unreachable/unreachable-code.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/unreachable-code.rs:5:3
+   |
+LL |   loop{}
+   |   ^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/unreachable/unreachable-in-call.stderr b/src/test/ui/unreachable/unreachable-in-call.stderr
index c740011c4a1..928f5634a12 100644
--- a/src/test/ui/unreachable/unreachable-in-call.stderr
+++ b/src/test/ui/unreachable/unreachable-in-call.stderr
@@ -9,12 +9,23 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/unreachable-in-call.rs:13:10
+   |
+LL |     call(diverge(),
+   |          ^^^^^^^^^
 
 error: unreachable call
   --> $DIR/unreachable-in-call.rs:17:5
    |
 LL |     call(
    |     ^^^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/unreachable-in-call.rs:19:9
+   |
+LL |         diverge());
+   |         ^^^^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/unreachable/unreachable-try-pattern.stderr b/src/test/ui/unreachable/unreachable-try-pattern.stderr
index 758aa5a45bc..889df790124 100644
--- a/src/test/ui/unreachable/unreachable-try-pattern.stderr
+++ b/src/test/ui/unreachable/unreachable-try-pattern.stderr
@@ -9,6 +9,11 @@ note: lint level defined here
    |
 LL | #![warn(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/unreachable-try-pattern.rs:19:36
+   |
+LL |     let y = (match x { Ok(n) => Ok(n as u32), Err(e) => Err(e) })?;
+   |                                    ^
 
 warning: unreachable pattern
   --> $DIR/unreachable-try-pattern.rs:19:24
diff --git a/src/test/ui/unreachable/unwarned-match-on-never.stderr b/src/test/ui/unreachable/unwarned-match-on-never.stderr
index ccb70d74311..9ce6e3df804 100644
--- a/src/test/ui/unreachable/unwarned-match-on-never.stderr
+++ b/src/test/ui/unreachable/unwarned-match-on-never.stderr
@@ -9,12 +9,23 @@ note: lint level defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+note: any code following this expression is unreachable
+  --> $DIR/unwarned-match-on-never.rs:8:11
+   |
+LL |     match x {}
+   |           ^
 
 error: unreachable arm
   --> $DIR/unwarned-match-on-never.rs:15:15
    |
 LL |         () => ()
    |               ^^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/unwarned-match-on-never.rs:14:11
+   |
+LL |     match (return) {
+   |           ^^^^^^^^
 
 error: unreachable expression
   --> $DIR/unwarned-match-on-never.rs:21:5
@@ -23,6 +34,12 @@ LL | /     match () {
 LL | |         () => (),
 LL | |     }
    | |_____^
+   |
+note: any code following this expression is unreachable
+  --> $DIR/unwarned-match-on-never.rs:20:5
+   |
+LL |     return;
+   |     ^^^^^^
 
 error: aborting due to 3 previous errors