Further tweak labels

Author: estebank

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1585,7 +1585,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             _ => {
                 if let Some((sp, msg)) = secondary_span {
                     if swap_secondary_and_primary {
-                        diag.span_label(sp, terr.to_string());
+                        let terr = if let Some(infer::ValuePairs::Types(infer::ExpectedFound {
+                            expected,
+                            ..
+                        })) = values
+                        {
+                            format!("expected this to be `{}`", expected)
+                        } else {
+                            terr.to_string()
+                        };
+                        diag.span_label(sp, terr);
                         diag.span_label(span, msg);
                     } else {
                         diag.span_label(span, terr.to_string());

compiler/rustc_middle/src/ty/error.rs

@@ -115,17 +115,15 @@ impl<'tcx> fmt::Display for TypeError<'tcx> {
             ArgumentMutability(_) | Mutability => write!(f, "types differ in mutability"),
             TupleSize(values) => write!(
                 f,
-                "expected a tuple with {} element{}, \
-                           found one with {} element{}",
+                "expected a tuple with {} element{}, found one with {} element{}",
                 values.expected,
                 pluralize!(values.expected),
                 values.found,
                 pluralize!(values.found)
             ),
             FixedArraySize(values) => write!(
                 f,
-                "expected an array with a fixed size of {} element{}, \
-                           found one with {} element{}",
+                "expected an array with a fixed size of {} element{}, found one with {} element{}",
                 values.expected,
                 pluralize!(values.expected),
                 values.found,

src/test/ui/associated-types/associated-types-binding-to-type-defined-in-supertrait.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `<ModelT as Vehicle>::Color == Blue`
   --> $DIR/associated-types-binding-to-type-defined-in-supertrait.rs:31:10
    |
 LL | impl Vehicle for ModelT { type Color = Black; }
-   |                                        ----- expected struct `Blue`, found struct `Black`
+   |                                        ----- expected this to be `Blue`
 ...
 LL | fn blue_car<C:Car<Color=Blue>>(c: C) {
    |                   ---------- required by this bound in `blue_car`
@@ -14,7 +14,7 @@ error[E0271]: type mismatch resolving `<ModelU as Vehicle>::Color == Black`
   --> $DIR/associated-types-binding-to-type-defined-in-supertrait.rs:32:10
    |
 LL | impl Vehicle for ModelU { type Color = Blue; }
-   |                                        ---- expected struct `Black`, found struct `Blue`
+   |                                        ---- expected this to be `Black`
 ...
 LL | fn black_car<C:Car<Color=Black>>(c: C) {
    |                    ----------- required by this bound in `black_car`

src/test/ui/associated-types/associated-types-eq-3.stderr

@@ -17,7 +17,7 @@ error[E0271]: type mismatch resolving `<isize as Foo>::A == Bar`
   --> $DIR/associated-types-eq-3.rs:38:5
    |
 LL |     type A = usize;
-   |              ----- expected struct `Bar`, found `usize`
+   |              ----- expected this to be `Bar`
 ...
 LL | fn foo1<I: Foo<A=Bar>>(x: I) {
    |                ----- required by this bound in `foo1`
@@ -29,7 +29,7 @@ error[E0271]: type mismatch resolving `<isize as Foo>::A == Bar`
   --> $DIR/associated-types-eq-3.rs:40:9
    |
 LL |     type A = usize;
-   |              ----- expected struct `Bar`, found `usize`
+   |              ----- expected this to be `Bar`
 ...
 LL |     baz(&a);
    |         ^^ type mismatch resolving `<isize as Foo>::A == Bar`

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:87:5
    |
 LL |     type A = &'a usize;
-   |              --------- expected `isize`, found `usize`
+   |              --------- expected this to be `&isize`
 ...
 LL | fn foo<T>()
    |    --- required by a bound in this
@@ -20,7 +20,7 @@ error[E0271]: type mismatch resolving `for<'x> <IntStruct as TheTrait<&'x isize>
   --> $DIR/associated-types-eq-hr.rs:91:5
    |
 LL |     type A = &'a isize;
-   |              --------- expected `usize`, found `isize`
+   |              --------- expected this to be `&usize`
 ...
 LL | fn bar<T>()
    |    --- required by a bound in this

src/test/ui/associated-types/associated-types-issue-20346.stderr

@@ -5,7 +5,7 @@ LL | fn is_iterator_of<A, I: Iterator<Item=A>>(_: &I) {}
    |                                  ------ required by this bound in `is_iterator_of`
 ...
 LL |     type Item = T;
-   |                 - expected enum `Option`, found type parameter `T`
+   |                 - expected this to be `Option<T>`
 ...
 LL | fn test_adapter<T, I: Iterator<Item=Option<T>>>(it: I) {
    |                 - this type parameter

src/test/ui/associated-types/issue-44153.stderr

@@ -5,7 +5,7 @@ LL |     fn visit() {}
    |     ---------- required by `Visit::visit`
 ...
 LL |     type Element = ();
-   |                    -- expected `&()`, found `()`
+   |                    -- expected this to be `&()`
 ...
 LL |     <() as Visit>::visit();
    |     ^^^^^^^^^^^^^^^^^^^^ type mismatch resolving `<() as Array>::Element == &()`

src/test/ui/associated-types/issue-72806.stderr

@@ -8,7 +8,7 @@ LL |     type Sibling = Foo2;
    |                    ^^^^ type mismatch resolving `<Foo2 as Bar2>::Ok == char`
 ...
 LL |     type Ok = u32;
-   |               --- expected `char`, found `u32`
+   |               --- expected this to be `char`
 
 error: aborting due to previous error
 

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

@@ -8,7 +8,7 @@ LL |     type Sibling = Foo2;
    |                    ^^^^ type mismatch resolving `<Foo2 as Bar2>::Ok == ()`
 ...
 LL |     type Ok = u32;
-   |               --- expected `()`, found `u32`
+   |               --- expected this to be `()`
 
 error: aborting due to previous error
 

src/test/ui/error-codes/E0271.stderr

@@ -5,7 +5,7 @@ LL | fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {
    |                                ------------------ required by this bound in `foo`
 ...
 LL | impl Trait for i8 { type AssociatedType = &'static str; }
-   |                                           ------------ expected `u32`, found `&str`
+   |                                           ------------ expected this to be `u32`
 ...
 LL |     foo(3_i8);
    |     ^^^ type mismatch resolving `<i8 as Trait>::AssociatedType == u32`

src/test/ui/generic-associated-types/issue-74684-2.stderr

@@ -11,7 +11,7 @@ error[E0271]: type mismatch resolving `<{integer} as Fun>::F<'_> == [u8]`
   --> $DIR/issue-74684-2.rs:24:5
    |
 LL |     type F<'a> = i32;
-   |                  --- expected slice `[u8]`, found `i32`
+   |                  --- expected this to be `[u8]`
 ...
 LL | fn bug<'a, T: ?Sized + Fun<F<'a> = [u8]>>(t: Box<T>) -> &'static T::F<'a> {
    |                            ------------ required by this bound in `bug`

src/test/ui/hrtb/issue-62203-hrtb-ice.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `for<'r> <L<[closure@$DIR/issue-62203-hrtb
   --> $DIR/issue-62203-hrtb-ice.rs:38:19
    |
 LL |     type O = T::Output;
-   |              --------- expected struct `Unit4`, found associated type
+   |              --------- expected this to be `Unit4`
 ...
 LL |     let v = Unit2.m(
    |                   ^ type mismatch resolving `for<'r> <L<[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39]> as T0<'r, (<Unit2 as Ty<'r>>::V,)>>::O == <_ as Ty<'r>>::V`

src/test/ui/impl-trait/bound-normalization-fail.stderr

@@ -11,7 +11,7 @@ error[E0271]: type mismatch resolving `<Foo<()> as FooLike>::Output == <T as imp
   --> $DIR/bound-normalization-fail.rs:26:32
    |
 LL |     type Output = T;
-   |                   - expected associated type, found `()`
+   |                   - expected this to be `<T as impl_trait::Trait>::Assoc`
 ...
 LL |     fn foo_fail<T: Trait>() -> impl FooLike<Output=T::Assoc> {
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type mismatch resolving `<Foo<()> as FooLike>::Output == <T as impl_trait::Trait>::Assoc`
@@ -33,7 +33,7 @@ error[E0271]: type mismatch resolving `<Foo<()> as FooLike>::Output == <T as lif
   --> $DIR/bound-normalization-fail.rs:42:41
    |
 LL |     type Output = T;
-   |                   - expected associated type, found `()`
+   |                   - expected this to be `<T as lifetimes::Trait<'static>>::Assoc`
 ...
 LL |     fn foo2_fail<'a, T: Trait<'a>>() -> impl FooLike<Output=T::Assoc> {
    |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type mismatch resolving `<Foo<()> as FooLike>::Output == <T as lifetimes::Trait<'static>>::Assoc`

src/test/ui/impl-trait/projection-mismatch-in-impl-where-clause.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `<() as Super>::Assoc == ()`
   --> $DIR/projection-mismatch-in-impl-where-clause.rs:13:14
    |
 LL |     type Assoc = u8;
-   |                  -- expected `()`, found `u8`
+   |                  -- expected this to be `()`
 ...
 LL | fn test() -> impl Test {
    |              ^^^^^^^^^ type mismatch resolving `<() as Super>::Assoc == ()`

src/test/ui/issues/issue-39970.stderr

@@ -5,7 +5,7 @@ LL |     fn visit() {}
    |     ---------- required by `Visit::visit`
 ...
 LL |     type Element = &'a ();
-   |                    ------ expected `()`, found `&()`
+   |                    ------ expected this to be `()`
 ...
 LL |     <() as Visit>::visit();
    |     ^^^^^^^^^^^^^^^^^^^^ type mismatch resolving `for<'a> <() as Array<'a>>::Element == ()`

src/test/ui/traits/associated_type_bound/check-trait-object-bounds-5.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `<i32 as Is>::T == i64`
   --> $DIR/check-trait-object-bounds-5.rs:23:5
    |
 LL |     type T = U;
-   |              - expected `i64`, found `i32`
+   |              - expected this to be `i64`
 ...
 LL | fn is_obj<T: ?Sized + Obj>(_: &T) {}
    |                       --- required by this bound in `is_obj`

src/test/ui/traits/associated_type_bound/check-trait-object-bounds-6.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `<i32 as Is>::T == i64`
   --> $DIR/check-trait-object-bounds-6.rs:20:5
    |
 LL |     type T = U;
-   |              - expected `i64`, found `i32`
+   |              - expected this to be `i64`
 ...
 LL | fn is_obj<T: ?Sized + Obj>(_: &T) {}
    |                       --- required by this bound in `is_obj`