Point at variant on pattern field count mismatch

Author: estebank

src/librustc_typeck/check/pat.rs

@@ -677,12 +677,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         } else {
             let subpats_ending = if subpats.len() == 1 { "" } else { "s" };
             let fields_ending = if variant.fields.len() == 1 { "" } else { "s" };
+            let span = tcx.def_span(res.def_id());
             struct_span_err!(tcx.sess, pat.span, E0023,
                              "this pattern has {} field{}, but the corresponding {} has {} field{}",
                              subpats.len(), subpats_ending, res.descr(),
                              variant.fields.len(),  fields_ending)
                 .span_label(pat.span, format!("expected {} field{}, found {}",
                                               variant.fields.len(), fields_ending, subpats.len()))
+                .span_label(span, format!("{} defined here", res.descr()))
                 .emit();
             on_error();
             return tcx.types.err;

src/test/ui/error-codes/E0023.stderr

@@ -1,18 +1,27 @@
 error[E0023]: this pattern has 1 field, but the corresponding tuple variant has 2 fields
   --> $DIR/E0023.rs:10:9
    |
+LL |     Apple(String, String),
+   |     --------------------- tuple variant defined here
+...
 LL |         Fruit::Apple(a) => {},
    |         ^^^^^^^^^^^^^^^ expected 2 fields, found 1
 
 error[E0023]: this pattern has 3 fields, but the corresponding tuple variant has 2 fields
   --> $DIR/E0023.rs:11:9
    |
+LL |     Apple(String, String),
+   |     --------------------- tuple variant defined here
+...
 LL |         Fruit::Apple(a, b, c) => {},
    |         ^^^^^^^^^^^^^^^^^^^^^ expected 2 fields, found 3
 
 error[E0023]: this pattern has 2 fields, but the corresponding tuple variant has 1 field
   --> $DIR/E0023.rs:12:9
    |
+LL |     Pear(u32),
+   |     --------- tuple variant defined here
+...
 LL |         Fruit::Pear(1, 2) => {},
    |         ^^^^^^^^^^^^^^^^^ expected 1 field, found 2
 

src/test/ui/match/match-pattern-field-mismatch.stderr

@@ -1,6 +1,9 @@
 error[E0023]: this pattern has 2 fields, but the corresponding tuple variant has 3 fields
   --> $DIR/match-pattern-field-mismatch.rs:10:11
    |
+LL |         Rgb(usize, usize, usize),
+   |         ------------------------ tuple variant defined here
+...
 LL |           Color::Rgb(_, _) => { }
    |           ^^^^^^^^^^^^^^^^ expected 3 fields, found 2
 

src/test/ui/pattern/pat-tuple-overfield.stderr

@@ -19,12 +19,18 @@ LL |         (1, 2, .., 3, 4) => {}
 error[E0023]: this pattern has 4 fields, but the corresponding tuple struct has 3 fields
   --> $DIR/pat-tuple-overfield.rs:10:9
    |
+LL | struct S(u8, u8, u8);
+   | --------------------- tuple struct defined here
+...
 LL |         S(1, 2, 3, 4) => {}
    |         ^^^^^^^^^^^^^ expected 3 fields, found 4
 
 error[E0023]: this pattern has 4 fields, but the corresponding tuple struct has 3 fields
   --> $DIR/pat-tuple-overfield.rs:12:9
    |
+LL | struct S(u8, u8, u8);
+   | --------------------- tuple struct defined here
+...
 LL |         S(1, 2, .., 3, 4) => {}
    |         ^^^^^^^^^^^^^^^^^ expected 3 fields, found 4
 

src/test/ui/pattern/pattern-error-continue.stderr

@@ -15,6 +15,9 @@ LL |         A::D(_) => (),
 error[E0023]: this pattern has 3 fields, but the corresponding tuple variant has 2 fields
   --> $DIR/pattern-error-continue.rs:17:9
    |
+LL |     B(isize, isize),
+   |     --------------- tuple variant defined here
+...
 LL |         A::B(_, _, _) => (),
    |         ^^^^^^^^^^^^^ expected 2 fields, found 3