Add label to item source of bound obligation

Author: estebank

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -1532,14 +1532,14 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let item_name = tcx.def_path_str(item_def_id);
                 let msg = format!("required by this bound in `{}`", item_name);
                 if let Some(ident) = tcx.opt_item_name(item_def_id) {
-                    let sm = self.tcx.sess.source_map();
+                    let sm = tcx.sess.source_map();
                     let same_line =
                         match (sm.lookup_line(ident.span.hi()), sm.lookup_line(span.lo())) {
                             (Ok(l), Ok(r)) => l.line == r.line,
                             _ => true,
                         };
                     if !ident.span.overlaps(span) && !same_line {
-                        err.span_label(ident.span, "");
+                        err.span_label(ident.span, "required by a bound in this");
                     }
                 }
                 if span != DUMMY_SP {

src/test/ui/associated-type-bounds/bad-bounds-on-assoc-in-trait.stderr

@@ -2,7 +2,7 @@ error[E0277]: `<L1 as Lam<&'a u8>>::App` doesn't implement `std::fmt::Debug`
   --> $DIR/bad-bounds-on-assoc-in-trait.rs:31:6
    |
 LL | trait Case1 {
-   |       -----
+   |       ----- required by a bound in this
 ...
 LL |                 Debug
    |                 ----- required by this bound in `Case1`
@@ -26,7 +26,7 @@ error[E0277]: `<<T as Case1>::C as std::iter::Iterator>::Item` cannot be sent be
   --> $DIR/bad-bounds-on-assoc-in-trait.rs:36:20
    |
 LL | trait Case1 {
-   |       -----
+   |       ----- required by a bound in this
 LL |     type C: Clone + Iterator<Item:
 LL |         Send + Iterator<Item:
    |         ---- required by this bound in `Case1`
@@ -42,7 +42,7 @@ error[E0277]: `<<T as Case1>::C as std::iter::Iterator>::Item` cannot be shared
   --> $DIR/bad-bounds-on-assoc-in-trait.rs:36:20
    |
 LL | trait Case1 {
-   |       -----
+   |       ----- required by a bound in this
 ...
 LL |         > + Sync>;
    |             ---- required by this bound in `Case1`
@@ -58,7 +58,7 @@ error[E0277]: `<_ as Lam<&'a u8>>::App` doesn't implement `std::fmt::Debug`
   --> $DIR/bad-bounds-on-assoc-in-trait.rs:36:20
    |
 LL | trait Case1 {
-   |       -----
+   |       ----- required by a bound in this
 ...
 LL |                 Debug
    |                 ----- required by this bound in `Case1`

src/test/ui/associated-types/associated-types-eq-hr.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `for<'x> <UintStruct as TheTrait<&'x isize
   --> $DIR/associated-types-eq-hr.rs:82:5
    |
 LL | fn foo<T>()
-   |    ---
+   |    --- required by a bound in this
 LL |     where T : for<'x> TheTrait<&'x isize, A = &'x isize>
    |                                           ------------- required by this bound in `foo`
 ...
@@ -16,7 +16,7 @@ error[E0271]: type mismatch resolving `for<'x> <IntStruct as TheTrait<&'x isize>
   --> $DIR/associated-types-eq-hr.rs:86:5
    |
 LL | fn bar<T>()
-   |    ---
+   |    --- required by a bound in this
 LL |     where T : for<'x> TheTrait<&'x isize, A = &'x usize>
    |                                           ------------- required by this bound in `bar`
 ...
@@ -30,7 +30,7 @@ error[E0277]: the trait bound `for<'x, 'y> Tuple: TheTrait<(&'x isize, &'y isize
   --> $DIR/associated-types-eq-hr.rs:91:17
    |
 LL | fn tuple_one<T>()
-   |    ---------
+   |    --------- required by a bound in this
 LL |     where T : for<'x,'y> TheTrait<(&'x isize, &'y isize), A = &'x isize>
    |               ---------------------------------------------------------- required by this bound in `tuple_one`
 ...
@@ -44,7 +44,7 @@ error[E0271]: type mismatch resolving `for<'x, 'y> <Tuple as TheTrait<(&'x isize
   --> $DIR/associated-types-eq-hr.rs:91:5
    |
 LL | fn tuple_one<T>()
-   |    ---------
+   |    --------- required by a bound in this
 LL |     where T : for<'x,'y> TheTrait<(&'x isize, &'y isize), A = &'x isize>
    |                                                           ------------- required by this bound in `tuple_one`
 ...
@@ -55,7 +55,7 @@ error[E0277]: the trait bound `for<'x, 'y> Tuple: TheTrait<(&'x isize, &'y isize
   --> $DIR/associated-types-eq-hr.rs:97:17
    |
 LL | fn tuple_two<T>()
-   |    ---------
+   |    --------- required by a bound in this
 LL |     where T : for<'x,'y> TheTrait<(&'x isize, &'y isize), A = &'y isize>
    |               ---------------------------------------------------------- required by this bound in `tuple_two`
 ...
@@ -69,7 +69,7 @@ error[E0271]: type mismatch resolving `for<'x, 'y> <Tuple as TheTrait<(&'x isize
   --> $DIR/associated-types-eq-hr.rs:97:5
    |
 LL | fn tuple_two<T>()
-   |    ---------
+   |    --------- required by a bound in this
 LL |     where T : for<'x,'y> TheTrait<(&'x isize, &'y isize), A = &'y isize>
    |                                                           ------------- required by this bound in `tuple_two`
 ...
@@ -80,7 +80,7 @@ error[E0277]: the trait bound `for<'x, 'y> Tuple: TheTrait<(&'x isize, &'y isize
   --> $DIR/associated-types-eq-hr.rs:107:18
    |
 LL | fn tuple_four<T>()
-   |    ----------
+   |    ---------- required by a bound in this
 LL |     where T : for<'x,'y> TheTrait<(&'x isize, &'y isize)>
    |               ------------------------------------------- required by this bound in `tuple_four`
 ...

src/test/ui/associated-types/defaults-unsound-62211-1.stderr

@@ -43,7 +43,7 @@ error[E0277]: `T` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     + Display = Self;
    |       ------- required by this bound in `UncheckedCopy`
@@ -62,7 +62,7 @@ error[E0277]: the trait bound `T: std::ops::Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     + Deref<Target = str>
    |       ------------------- required by this bound in `UncheckedCopy`
@@ -79,7 +79,7 @@ error[E0277]: cannot add-assign `&'static str` to `T`
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     + AddAssign<&'static str>
    |       ----------------------- required by this bound in `UncheckedCopy`
@@ -97,7 +97,7 @@ error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     type Output: Copy
    |                  ---- required by this bound in `UncheckedCopy`

src/test/ui/associated-types/defaults-unsound-62211-2.stderr

@@ -43,7 +43,7 @@ error[E0277]: `T` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     + Display = Self;
    |       ------- required by this bound in `UncheckedCopy`
@@ -62,7 +62,7 @@ error[E0277]: the trait bound `T: std::ops::Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     + Deref<Target = str>
    |       ------------------- required by this bound in `UncheckedCopy`
@@ -79,7 +79,7 @@ error[E0277]: cannot add-assign `&'static str` to `T`
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     + AddAssign<&'static str>
    |       ----------------------- required by this bound in `UncheckedCopy`
@@ -97,7 +97,7 @@ error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
 LL | trait UncheckedCopy: Sized {
-   |       -------------
+   |       ------------- required by a bound in this
 ...
 LL |     type Output: Copy
    |                  ---- required by this bound in `UncheckedCopy`

src/test/ui/associated-types/higher-ranked-projection.bad.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `for<'a> <&'a _ as Mirror>::Image == _`
   --> $DIR/higher-ranked-projection.rs:25:5
    |
 LL | fn foo<U, T>(_t: T)
-   |    ---
+   |    --- required by a bound in this
 LL |     where for<'a> &'a T: Mirror<Image=U>
    |                                 ------- required by this bound in `foo`
 ...

src/test/ui/associated-types/issue-43924.stderr

@@ -10,7 +10,7 @@ error[E0277]: the trait bound `(dyn std::string::ToString + 'static): std::defau
   --> $DIR/issue-43924.rs:10:6
    |
 LL | trait Foo<T: Default + ToString> {
-   |       ---
+   |       --- required by a bound in this
 LL |     type Out: Default + ToString + ?Sized = dyn ToString;
    |               ------- required by this bound in `Foo`
 ...
@@ -21,7 +21,7 @@ error[E0277]: the trait bound `(dyn std::string::ToString + 'static): std::defau
   --> $DIR/issue-43924.rs:11:6
    |
 LL | trait Foo<T: Default + ToString> {
-   |       ---
+   |       --- required by a bound in this
 LL |     type Out: Default + ToString + ?Sized = dyn ToString;
    |               ------- required by this bound in `Foo`
 ...

src/test/ui/associated-types/issue-65774-1.stderr

@@ -10,7 +10,7 @@ error[E0277]: the trait bound `T: MyDisplay` is not satisfied
   --> $DIR/issue-65774-1.rs:16:6
    |
 LL | trait MPU {
-   |       ---
+   |       --- required by a bound in this
 LL |     type MpuConfig: MyDisplay = T;
    |                     --------- required by this bound in `MPU`
 ...

src/test/ui/associated-types/issue-65774-2.stderr

@@ -10,7 +10,7 @@ error[E0277]: the trait bound `T: MyDisplay` is not satisfied
   --> $DIR/issue-65774-2.rs:16:6
    |
 LL | trait MPU {
-   |       ---
+   |       --- required by a bound in this
 LL |     type MpuConfig: MyDisplay = T;
    |                     --------- required by this bound in `MPU`
 ...

src/test/ui/associated-types/point-at-type-on-obligation-failure-2.stderr

@@ -2,7 +2,7 @@ error[E0277]: the trait bound `bool: Bar` is not satisfied
   --> $DIR/point-at-type-on-obligation-failure-2.rs:8:18
    |
 LL | trait Foo {
-   |       ---
+   |       --- required by a bound in this
 LL |     type Assoc: Bar;
    |                 --- required by this bound in `Foo`
 ...