Don't add label to the match expr when the type is not fully realized

Author: estebank

src/librustc/infer/error_reporting/mod.rs

@@ -488,7 +488,9 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     fn note_error_origin(&self, err: &mut DiagnosticBuilder<'tcx>, cause: &ObligationCause<'tcx>) {
         match cause.code {
             ObligationCauseCode::MatchExpressionArmPattern { span, ty } => {
-                err.span_label(span, format!("this match expression has type `{}`", ty));
+                if ty.is_suggestable() {  // don't show type `_`
+                    err.span_label(span, format!("this match expression has type `{}`", ty));
+                }
             }
             ObligationCauseCode::MatchExpressionArm { arm_span, source } => match source {
                 hir::MatchSource::IfLetDesugar { .. } => {

src/test/ui/match/match-range-fail.stderr

@@ -19,8 +19,6 @@ LL |         10 ..= "what" => ()
 error[E0308]: mismatched types
   --> $DIR/match-range-fail.rs:17:9
    |
-LL |     match 5 {
-   |           - this match expression has type `{integer}`
 LL |         'c' ..= 100 => { }
    |         ^^^^^^^^^^^ expected integer, found char
    |

src/test/ui/mismatched_types/E0409.stderr

@@ -9,8 +9,6 @@ LL |         (0, ref y) | (y, 0) => {} //~ ERROR E0409
 error[E0308]: mismatched types
   --> $DIR/E0409.rs:5:23
    |
-LL |     match x {
-   |           - this match expression has type `_`
 LL |         (0, ref y) | (y, 0) => {} //~ ERROR E0409
    |                       ^ expected &{integer}, found integer
    |

src/test/ui/or-pattern-mismatch.stderr

@@ -2,9 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/or-pattern-mismatch.rs:3:68
    |
 LL | fn main() { match Blah::A(1, 1, 2) { Blah::A(_, x, y) | Blah::B(x, y) => { } } }
-   |                   ----------------                                 ^ expected usize, found isize
-   |                   |
-   |                   this match expression has type `_`
+   |                                                                    ^ expected usize, found isize
    |
    = note: expected type `usize`
               found type `isize`

src/test/ui/resolve/resolve-inconsistent-binding-mode.stderr

@@ -23,8 +23,6 @@ LL |       Opts::A(ref mut i) | Opts::B(ref i) => {}
 error[E0308]: mismatched types
   --> $DIR/resolve-inconsistent-binding-mode.rs:7:32
    |
-LL |     match x {
-   |           - this match expression has type `_`
 LL |       Opts::A(ref i) | Opts::B(i) => {}
    |                                ^ expected &isize, found isize
    |
@@ -34,8 +32,6 @@ LL |       Opts::A(ref i) | Opts::B(i) => {}
 error[E0308]: mismatched types
   --> $DIR/resolve-inconsistent-binding-mode.rs:16:32
    |
-LL |     match x {
-   |           - this match expression has type `_`
 LL |       Opts::A(ref i) | Opts::B(i) => {}
    |                                ^ expected &isize, found isize
    |
@@ -45,8 +41,6 @@ LL |       Opts::A(ref i) | Opts::B(i) => {}
 error[E0308]: mismatched types
   --> $DIR/resolve-inconsistent-binding-mode.rs:25:36
    |
-LL |     match x {
-   |           - this match expression has type `_`
 LL |       Opts::A(ref mut i) | Opts::B(ref i) => {}
    |                                    ^^^^^ types differ in mutability
    |