Modify mismatched type error for functions with no return

[estebank]

Fix #50009.

error[E0308]: mismatched types
  --> $DIR/coercion-missing-tail-expected-type.rs:3:24
   |
LL | fn plus_one(x: i32) -> i32 { //~ ERROR mismatched types
   |    --------            ^^^ expected i32, found ()
   |    |
   |    this function's body doesn't return
LL |     x + 1;
   |          - help: consider removing this semicolon
   |
   = note: expected type `i32`
              found type `()`

instead of

error[E0308]: mismatched types
  --> $DIR/coercion-missing-tail-expected-type.rs:3:28
   |
LL |   fn plus_one(x: i32) -> i32 { //~ ERROR mismatched types
   |  ____________________________^
LL | |     x + 1;
   | |          - help: consider removing this semicolon
LL | | }
   | |_^ expected i32, found ()
   |
   = note: expected type `i32`
              found type `()`

[rust-highfive]

r? @varkor

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[estebank]

CC @zackmdavis @petrochenkov @nikomatsakis for input (as this might be a more contentious change).

[varkor]

This style of suggestions definitely looks more readable to me! I just have one query about test/ui/liveness/liveness-forgot-ret.stderr, but other than that, the changes look good.

[varkor]

@bors r+

[bors]

📌 Commit 211365d has been approved by varkor

[bors]

⌛ Testing commit 211365d with merge ad9068f...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: varkor
Pushing ad9068f to master...