Rollup merge of #84014 - estebank:cool-bears-hot-tip, r=varkor

Improve trait/impl method discrepancy errors

* Use more accurate spans
* Clean up some code by removing previous hack
* Provide structured suggestions

Structured suggestions are particularly useful for cases where arbitrary self types are used, like in custom `Future`s, because the way to write `self: Pin<&mut Self>` is not necessarily self-evident when first encountered.

13 files changed, 155 insertions, 31 deletions

diff --git a/src/test/ui/associated-types/defaults-specialization.stderr b/src/test/ui/associated-types/defaults-specialization.stderr
index 920f8322813..3c7dc1fc3c9 100644
--- a/src/test/ui/associated-types/defaults-specialization.stderr
+++ b/src/test/ui/associated-types/defaults-specialization.stderr
@@ -15,7 +15,10 @@ LL |     fn make() -> Self::Ty {
    |                  -------- type in trait
 ...
 LL |     fn make() -> u8 { 0 }
-   |                  ^^ expected associated type, found `u8`
+   |                  ^^
+   |                  |
+   |                  expected associated type, found `u8`
+   |                  help: change the output type to match the trait: `<A<T> as Tr>::Ty`
    |
    = note: expected fn pointer `fn() -> <A<T> as Tr>::Ty`
               found fn pointer `fn() -> u8`
@@ -30,7 +33,10 @@ LL |     default type Ty = bool;
    |     ----------------------- expected this associated type
 LL | 
 LL |     fn make() -> bool { true }
-   |                  ^^^^ expected associated type, found `bool`
+   |                  ^^^^
+   |                  |
+   |                  expected associated type, found `bool`
+   |                  help: change the output type to match the trait: `<B<T> as Tr>::Ty`
    |
    = note: expected fn pointer `fn() -> <B<T> as Tr>::Ty`
               found fn pointer `fn() -> bool`
diff --git a/src/test/ui/compare-method/bad-self-type.rs b/src/test/ui/compare-method/bad-self-type.rs
new file mode 100644
index 00000000000..f42a9e49abd
--- /dev/null
+++ b/src/test/ui/compare-method/bad-self-type.rs
@@ -0,0 +1,26 @@
+use std::future::Future;
+use std::task::{Context, Poll};
+
+fn main() {}
+
+struct MyFuture {}
+
+impl Future for MyFuture {
+    type Output = ();
+    fn poll(self, _: &mut Context<'_>) -> Poll<()> {
+    //~^ ERROR method `poll` has an incompatible type for trait
+        todo!()
+    }
+}
+
+trait T {
+    fn foo(self);
+    fn bar(self) -> Option<()>;
+}
+
+impl T for MyFuture {
+    fn foo(self: Box<Self>) {}
+    //~^ ERROR method `foo` has an incompatible type for trait
+    fn bar(self) {}
+    //~^ ERROR method `bar` has an incompatible type for trait
+}
diff --git a/src/test/ui/compare-method/bad-self-type.stderr b/src/test/ui/compare-method/bad-self-type.stderr
new file mode 100644
index 00000000000..76f91fbf241
--- /dev/null
+++ b/src/test/ui/compare-method/bad-self-type.stderr
@@ -0,0 +1,46 @@
+error[E0053]: method `poll` has an incompatible type for trait
+  --> $DIR/bad-self-type.rs:10:13
+   |
+LL |     fn poll(self, _: &mut Context<'_>) -> Poll<()> {
+   |             ^^^^
+   |             |
+   |             expected struct `Pin`, found struct `MyFuture`
+   |             help: change the self-receiver type to match the trait: `self: Pin<&mut MyFuture>`
+   |
+   = note: expected fn pointer `fn(Pin<&mut MyFuture>, &mut Context<'_>) -> Poll<_>`
+              found fn pointer `fn(MyFuture, &mut Context<'_>) -> Poll<_>`
+
+error[E0053]: method `foo` has an incompatible type for trait
+  --> $DIR/bad-self-type.rs:22:18
+   |
+LL |     fn foo(self);
+   |            ---- type in trait
+...
+LL |     fn foo(self: Box<Self>) {}
+   |            ------^^^^^^^^^
+   |            |     |
+   |            |     expected struct `MyFuture`, found struct `Box`
+   |            help: change the self-receiver type to match the trait: `self`
+   |
+   = note: expected fn pointer `fn(MyFuture)`
+              found fn pointer `fn(Box<MyFuture>)`
+
+error[E0053]: method `bar` has an incompatible type for trait
+  --> $DIR/bad-self-type.rs:24:18
+   |
+LL |     fn bar(self) -> Option<()>;
+   |                     ---------- type in trait
+...
+LL |     fn bar(self) {}
+   |                  ^ expected enum `Option`, found `()`
+   |
+   = note: expected fn pointer `fn(MyFuture) -> Option<()>`
+              found fn pointer `fn(MyFuture)`
+help: change the output type to match the trait
+   |
+LL |     fn bar(self) -> Option<()> {}
+   |                  ^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0053`.
diff --git a/src/test/ui/compare-method/reordered-type-param.stderr b/src/test/ui/compare-method/reordered-type-param.stderr
index f1f8a663f21..d581628ea48 100644
--- a/src/test/ui/compare-method/reordered-type-param.stderr
+++ b/src/test/ui/compare-method/reordered-type-param.stderr
@@ -5,8 +5,10 @@ LL |   fn b<C:Clone,D>(&self, x: C) -> C;
    |                             - type in trait
 ...
 LL |   fn b<F:Clone,G>(&self, _x: G) -> G { panic!() }
-   |        -       -             ^ expected type parameter `F`, found type parameter `G`
-   |        |       |
+   |        -       -             ^
+   |        |       |             |
+   |        |       |             expected type parameter `F`, found type parameter `G`
+   |        |       |             help: change the parameter type to match the trait: `F`
    |        |       found type parameter
    |        expected type parameter
    |
diff --git a/src/test/ui/impl-trait/impl-generic-mismatch-ab.stderr b/src/test/ui/impl-trait/impl-generic-mismatch-ab.stderr
index 638a0093fb2..d37670db085 100644
--- a/src/test/ui/impl-trait/impl-generic-mismatch-ab.stderr
+++ b/src/test/ui/impl-trait/impl-generic-mismatch-ab.stderr
@@ -5,8 +5,10 @@ LL |     fn foo<A: Debug>(&self, a: &A, b: &impl Debug);
    |                                -- type in trait
 ...
 LL |     fn foo<B: Debug>(&self, a: &impl Debug, b: &B) { }
-   |            -                   ^^^^^^^^^^^ expected type parameter `B`, found type parameter `impl Debug`
-   |            |
+   |            -                   ^^^^^^^^^^^
+   |            |                   |
+   |            |                   expected type parameter `B`, found type parameter `impl Debug`
+   |            |                   help: change the parameter type to match the trait: `&B`
    |            expected type parameter
    |
    = note: expected fn pointer `fn(&(), &B, &impl Debug)`
diff --git a/src/test/ui/impl-trait/trait_type.stderr b/src/test/ui/impl-trait/trait_type.stderr
index 961bb735118..bea24339837 100644
--- a/src/test/ui/impl-trait/trait_type.stderr
+++ b/src/test/ui/impl-trait/trait_type.stderr
@@ -1,8 +1,11 @@
 error[E0053]: method `fmt` has an incompatible type for trait
-  --> $DIR/trait_type.rs:7:4
+  --> $DIR/trait_type.rs:7:21
    |
 LL |    fn fmt(&self, x: &str) -> () { }
-   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |                     ^^^^
+   |                     |
+   |                     types differ in mutability
+   |                     help: change the parameter type to match the trait: `&mut Formatter<'_>`
    |
    = note: expected fn pointer `fn(&MyType, &mut Formatter<'_>) -> Result<(), std::fmt::Error>`
               found fn pointer `fn(&MyType, &str)`
diff --git a/src/test/ui/issues/issue-13033.stderr b/src/test/ui/issues/issue-13033.stderr
index 57447fa48aa..6c3651ff121 100644
--- a/src/test/ui/issues/issue-13033.stderr
+++ b/src/test/ui/issues/issue-13033.stderr
@@ -8,7 +8,7 @@ LL |     fn bar(&mut self, other: &dyn Foo) {}
    |                              ^^^^^^^^
    |                              |
    |                              types differ in mutability
-   |                              help: consider changing the mutability to match the trait: `&mut dyn Foo`
+   |                              help: change the parameter type to match the trait: `&mut dyn Foo`
    |
    = note: expected fn pointer `fn(&mut Baz, &mut dyn Foo)`
               found fn pointer `fn(&mut Baz, &dyn Foo)`
diff --git a/src/test/ui/issues/issue-20225.stderr b/src/test/ui/issues/issue-20225.stderr
index 3bcc50ded84..6f4813ca623 100644
--- a/src/test/ui/issues/issue-20225.stderr
+++ b/src/test/ui/issues/issue-20225.stderr
@@ -1,33 +1,42 @@
 error[E0053]: method `call` has an incompatible type for trait
-  --> $DIR/issue-20225.rs:6:3
+  --> $DIR/issue-20225.rs:6:43
    |
 LL | impl<'a, T> Fn<(&'a T,)> for Foo {
    |          - this type parameter
 LL |   extern "rust-call" fn call(&self, (_,): (T,)) {}
-   |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&T`, found type parameter `T`
+   |                                           ^^^^
+   |                                           |
+   |                                           expected `&T`, found type parameter `T`
+   |                                           help: change the parameter type to match the trait: `(&'a T,)`
    |
    = note: expected fn pointer `extern "rust-call" fn(&Foo, (&'a T,))`
               found fn pointer `extern "rust-call" fn(&Foo, (T,))`
 
 error[E0053]: method `call_mut` has an incompatible type for trait
-  --> $DIR/issue-20225.rs:11:3
+  --> $DIR/issue-20225.rs:11:51
    |
 LL | impl<'a, T> FnMut<(&'a T,)> for Foo {
    |          - this type parameter
 LL |   extern "rust-call" fn call_mut(&mut self, (_,): (T,)) {}
-   |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&T`, found type parameter `T`
+   |                                                   ^^^^
+   |                                                   |
+   |                                                   expected `&T`, found type parameter `T`
+   |                                                   help: change the parameter type to match the trait: `(&'a T,)`
    |
    = note: expected fn pointer `extern "rust-call" fn(&mut Foo, (&'a T,))`
               found fn pointer `extern "rust-call" fn(&mut Foo, (T,))`
 
 error[E0053]: method `call_once` has an incompatible type for trait
-  --> $DIR/issue-20225.rs:18:3
+  --> $DIR/issue-20225.rs:18:47
    |
 LL | impl<'a, T> FnOnce<(&'a T,)> for Foo {
    |          - this type parameter
 ...
 LL |   extern "rust-call" fn call_once(self, (_,): (T,)) {}
-   |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&T`, found type parameter `T`
+   |                                               ^^^^
+   |                                               |
+   |                                               expected `&T`, found type parameter `T`
+   |                                               help: change the parameter type to match the trait: `(&'a T,)`
    |
    = note: expected fn pointer `extern "rust-call" fn(Foo, (&'a T,))`
               found fn pointer `extern "rust-call" fn(Foo, (T,))`
diff --git a/src/test/ui/issues/issue-21332.stderr b/src/test/ui/issues/issue-21332.stderr
index 35863fbebe3..d92966da17c 100644
--- a/src/test/ui/issues/issue-21332.stderr
+++ b/src/test/ui/issues/issue-21332.stderr
@@ -1,8 +1,11 @@
 error[E0053]: method `next` has an incompatible type for trait
-  --> $DIR/issue-21332.rs:5:5
+  --> $DIR/issue-21332.rs:5:27
    |
 LL |     fn next(&mut self) -> Result<i32, i32> { Ok(7) }
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected enum `Option`, found enum `Result`
+   |                           ^^^^^^^^^^^^^^^^
+   |                           |
+   |                           expected enum `Option`, found enum `Result`
+   |                           help: change the output type to match the trait: `Option<i32>`
    |
    = note: expected fn pointer `fn(&mut S) -> Option<i32>`
               found fn pointer `fn(&mut S) -> Result<i32, i32>`
diff --git a/src/test/ui/issues/issue-35869.stderr b/src/test/ui/issues/issue-35869.stderr
index f80561bf6be..71b2a9df095 100644
--- a/src/test/ui/issues/issue-35869.stderr
+++ b/src/test/ui/issues/issue-35869.stderr
@@ -5,7 +5,10 @@ LL |     fn foo(_: fn(u8) -> ());
    |               ------------ type in trait
 ...
 LL |     fn foo(_: fn(u16) -> ()) {}
-   |               ^^^^^^^^^^^^^ expected `u8`, found `u16`
+   |               ^^^^^^^^^^^^^
+   |               |
+   |               expected `u8`, found `u16`
+   |               help: change the parameter type to match the trait: `fn(u8)`
    |
    = note: expected fn pointer `fn(fn(u8))`
               found fn pointer `fn(fn(u16))`
@@ -17,7 +20,10 @@ LL |     fn bar(_: Option<u8>);
    |               ---------- type in trait
 ...
 LL |     fn bar(_: Option<u16>) {}
-   |               ^^^^^^^^^^^ expected `u8`, found `u16`
+   |               ^^^^^^^^^^^
+   |               |
+   |               expected `u8`, found `u16`
+   |               help: change the parameter type to match the trait: `Option<u8>`
    |
    = note: expected fn pointer `fn(Option<u8>)`
               found fn pointer `fn(Option<u16>)`
@@ -29,7 +35,10 @@ LL |     fn baz(_: (u8, u16));
    |               --------- type in trait
 ...
 LL |     fn baz(_: (u16, u16)) {}
-   |               ^^^^^^^^^^ expected `u8`, found `u16`
+   |               ^^^^^^^^^^
+   |               |
+   |               expected `u8`, found `u16`
+   |               help: change the parameter type to match the trait: `(u8, u16)`
    |
    = note: expected fn pointer `fn((u8, _))`
               found fn pointer `fn((u16, _))`
@@ -41,7 +50,10 @@ LL |     fn qux() -> u8;
    |                 -- type in trait
 ...
 LL |     fn qux() -> u16 { 5u16 }
-   |                 ^^^ expected `u8`, found `u16`
+   |                 ^^^
+   |                 |
+   |                 expected `u8`, found `u16`
+   |                 help: change the output type to match the trait: `u8`
    |
    = note: expected fn pointer `fn() -> u8`
               found fn pointer `fn() -> u16`
diff --git a/src/test/ui/mismatched_types/E0053.stderr b/src/test/ui/mismatched_types/E0053.stderr
index e0a3ce922b9..6ce8126b9f9 100644
--- a/src/test/ui/mismatched_types/E0053.stderr
+++ b/src/test/ui/mismatched_types/E0053.stderr
@@ -5,7 +5,10 @@ LL |     fn foo(x: u16);
    |               --- type in trait
 ...
 LL |     fn foo(x: i16) { }
-   |               ^^^ expected `u16`, found `i16`
+   |               ^^^
+   |               |
+   |               expected `u16`, found `i16`
+   |               help: change the parameter type to match the trait: `u16`
    |
    = note: expected fn pointer `fn(u16)`
               found fn pointer `fn(i16)`
@@ -20,7 +23,7 @@ LL |     fn bar(&mut self) { }
    |            ^^^^^^^^^
    |            |
    |            types differ in mutability
-   |            help: consider changing the mutability to match the trait: `&self`
+   |            help: change the self-receiver type to match the trait: `self: &Bar`
    |
    = note: expected fn pointer `fn(&Bar)`
               found fn pointer `fn(&mut Bar)`
diff --git a/src/test/ui/mismatched_types/trait-impl-fn-incompatibility.stderr b/src/test/ui/mismatched_types/trait-impl-fn-incompatibility.stderr
index 161843473b6..2ac4d1c33a9 100644
--- a/src/test/ui/mismatched_types/trait-impl-fn-incompatibility.stderr
+++ b/src/test/ui/mismatched_types/trait-impl-fn-incompatibility.stderr
@@ -5,7 +5,10 @@ LL |     fn foo(x: u16);
    |               --- type in trait
 ...
 LL |     fn foo(x: i16) { }
-   |               ^^^ expected `u16`, found `i16`
+   |               ^^^
+   |               |
+   |               expected `u16`, found `i16`
+   |               help: change the parameter type to match the trait: `u16`
    |
    = note: expected fn pointer `fn(u16)`
               found fn pointer `fn(i16)`
@@ -20,7 +23,7 @@ LL |     fn bar(&mut self, bar: &Bar) { }
    |                            ^^^^
    |                            |
    |                            types differ in mutability
-   |                            help: consider changing the mutability to match the trait: `&mut Bar`
+   |                            help: change the parameter type to match the trait: `&mut Bar`
    |
    = note: expected fn pointer `fn(&mut Bar, &mut Bar)`
               found fn pointer `fn(&mut Bar, &Bar)`
diff --git a/src/test/ui/wrong-mul-method-signature.stderr b/src/test/ui/wrong-mul-method-signature.stderr
index 4c367fb9e9c..9f8896f01ee 100644
--- a/src/test/ui/wrong-mul-method-signature.stderr
+++ b/src/test/ui/wrong-mul-method-signature.stderr
@@ -1,26 +1,35 @@
 error[E0053]: method `mul` has an incompatible type for trait
-  --> $DIR/wrong-mul-method-signature.rs:16:5
+  --> $DIR/wrong-mul-method-signature.rs:16:21
    |
 LL |     fn mul(self, s: &f64) -> Vec1 {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `f64`, found `&f64`
+   |                     ^^^^
+   |                     |
+   |                     expected `f64`, found `&f64`
+   |                     help: change the parameter type to match the trait: `f64`
    |
    = note: expected fn pointer `fn(Vec1, f64) -> Vec1`
               found fn pointer `fn(Vec1, &f64) -> Vec1`
 
 error[E0053]: method `mul` has an incompatible type for trait
-  --> $DIR/wrong-mul-method-signature.rs:33:5
+  --> $DIR/wrong-mul-method-signature.rs:33:21
    |
 LL |     fn mul(self, s: f64) -> Vec2 {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `Vec2`, found `f64`
+   |                     ^^^
+   |                     |
+   |                     expected struct `Vec2`, found `f64`
+   |                     help: change the parameter type to match the trait: `Vec2`
    |
    = note: expected fn pointer `fn(Vec2, Vec2) -> f64`
               found fn pointer `fn(Vec2, f64) -> Vec2`
 
 error[E0053]: method `mul` has an incompatible type for trait
-  --> $DIR/wrong-mul-method-signature.rs:52:5
+  --> $DIR/wrong-mul-method-signature.rs:52:29
    |
 LL |     fn mul(self, s: f64) -> f64 {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `f64`
+   |                             ^^^
+   |                             |
+   |                             expected `i32`, found `f64`
+   |                             help: change the output type to match the trait: `i32`
    |
    = note: expected fn pointer `fn(Vec3, _) -> i32`
               found fn pointer `fn(Vec3, _) -> f64`