Do not trigger unreachable lint in async body and Use span labels

Author: estebank

src/librustc_typeck/check/mod.rs

@@ -2340,16 +2340,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // 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.
-            if !span.is_desugaring(DesugaringKind::CondTemporary) {
+            if !span.is_desugaring(DesugaringKind::CondTemporary) &&
+                !span.is_desugaring(DesugaringKind::Async)
+            {
                 self.diverges.set(Diverges::WarnedAlways);
 
                 debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
 
                 let msg = format!("unreachable {}", kind);
                 self.tcx().struct_span_lint_hir(lint::builtin::UNREACHABLE_CODE, id, span, &msg)
-                    .span_note(
+                    .span_label(span, &msg)
+                    .span_label(
                         orig_span,
-                        custom_note.unwrap_or("any code following this expression is unreachable")
+                        custom_note.unwrap_or("any code following this expression is unreachable"),
                     )
                     .emit();
             }

src/test/ui/dead-code-ret.stderr

@@ -1,19 +1,16 @@
 error: unreachable statement
   --> $DIR/dead-code-ret.rs:7:5
    |
+LL |     return;
+   |     ------ any code following this expression is unreachable
 LL |     println!("Paul is dead");
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ unreachable statement
    |
 note: lint level defined here
   --> $DIR/dead-code-ret.rs:3:9
    |
 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

src/test/ui/if-ret.stderr

@@ -2,12 +2,9 @@ warning: unreachable block in `if` expression
   --> $DIR/if-ret.rs:6:24
    |
 LL | fn foo() { if (return) { } }
-   |                        ^^^
+   |               -------- ^^^ unreachable block in `if` expression
+   |               |
+   |               any code following this expression is unreachable
    |
    = 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) { } }
-   |               ^^^^^^^^
 

src/test/ui/issues/issue-2150.stderr

@@ -1,19 +1,16 @@
 error: unreachable statement
   --> $DIR/issue-2150.rs:8:5
    |
+LL |     panic!();
+   |     --------- any code following this expression is unreachable
 LL |     for x in &v { i += 1; }
-   |     ^^^^^^^^^^^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ unreachable statement
    |
 note: lint level defined here
   --> $DIR/issue-2150.rs:1:9
    |
 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

src/test/ui/issues/issue-7246.stderr

@@ -1,19 +1,16 @@
 error: unreachable statement
   --> $DIR/issue-7246.rs:7:5
    |
+LL |     return;
+   |     ------ any code following this expression is unreachable
 LL |     if *ptr::null() {};
-   |     ^^^^^^^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^^^^^^^ unreachable statement
    |
 note: lint level defined here
   --> $DIR/issue-7246.rs:1:9
    |
 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
 

src/test/ui/lint/lint-attr-non-item-node.stderr

@@ -1,19 +1,16 @@
 error: unreachable statement
   --> $DIR/lint-attr-non-item-node.rs:7:9
    |
+LL |         break;
+   |         ----- any code following this expression is unreachable
 LL |         "unreachable";
-   |         ^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^ unreachable statement
    |
 note: lint level defined here
   --> $DIR/lint-attr-non-item-node.rs:4:12
    |
 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
 

src/test/ui/lint/unreachable-async-fn.rs

@@ -0,0 +1,9 @@
+// run-pass
+// edition:2018
+#[allow(dead_code)]
+
+async fn foo () { // unreachable lint doesn't trigger
+   unimplemented!()
+}
+
+fn main() {}

src/test/ui/liveness/liveness-unused.stderr

@@ -1,20 +1,17 @@
 warning: unreachable statement
   --> $DIR/liveness-unused.rs:92:9
    |
+LL |         continue;
+   |         -------- any code following this expression is unreachable
 LL |         drop(*x as i32);
-   |         ^^^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^^ unreachable statement
    |
 note: lint level defined here
   --> $DIR/liveness-unused.rs:1:9
    |
 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

src/test/ui/match/match-no-arms-unreachable-after.stderr

@@ -1,19 +1,16 @@
 error: unreachable statement
   --> $DIR/match-no-arms-unreachable-after.rs:8:5
    |
+LL |     match v { }
+   |     ----------- any code following this expression is unreachable
 LL |     let x = 2;
-   |     ^^^^^^^^^^
+   |     ^^^^^^^^^^ unreachable statement
    |
 note: lint level defined here
   --> $DIR/match-no-arms-unreachable-after.rs:2:9
    |
 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
 

src/test/ui/never-assign-dead-code.stderr

@@ -1,33 +1,26 @@
 warning: unreachable statement
   --> $DIR/never-assign-dead-code.rs:10:5
    |
+LL |     let x: ! = panic!("aah");
+   |                ------------- any code following this expression is unreachable
 LL |     drop(x);
-   |     ^^^^^^^^
+   |     ^^^^^^^^ unreachable statement
    |
 note: lint level defined here
   --> $DIR/never-assign-dead-code.rs:5:9
    |
 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);
-   |          ^
+   |     ^^^^ - any code following this expression is unreachable
+   |     |
+   |     unreachable call
 
 warning: unused variable: `x`
   --> $DIR/never-assign-dead-code.rs:9:9