Rollup merge of #100479 - compiler-errors:argument-type-error-improvements, r=lcnr

Argument type error improvements

Motivated by this interesting code snippet:

```rust
#[derive(Copy, Clone)]
struct Wrapper<T>(T);

fn foo(_: fn(i32), _: Wrapper<i32>) {}

fn f(_: u32) {}

fn main() {
    let w = Wrapper::<isize>(1isize);
    foo(f, w);
}
```

Which currently errors like:
```
error[E0308]: arguments to this function are incorrect
  --> src/main.rs:10:5
   |
10 |     foo(f, w);
   |     ^^^ -  - expected `i32`, found `isize`
   |         |
   |         expected `i32`, found `u32`
   |
   = note: expected fn pointer `fn(i32)`
                 found fn item `fn(u32) {f}`
   = note: expected struct `Wrapper<i32>`
              found struct `Wrapper<isize>`
note: function defined here
  --> src/main.rs:4:4
   |
4  | fn foo(_: fn(i32), _: Wrapper<i32>) {}
   |    ^^^ ----------  ---------------
```

Specifically, that double `expected .. found ..` which is very difficult to correlate to the types in the arguments. Also, the fact that "expected `i32`, found `isize`" and the other argument mismatch label don't even really explain what's going on here.

After this PR:
```
error[E0308]: arguments to this function are incorrect
  --> $DIR/two-mismatch-notes.rs:10:5
   |
LL |     foo(f, w);
   |     ^^^
   |
note: expected fn pointer, found fn item
  --> $DIR/two-mismatch-notes.rs:10:9
   |
LL |     foo(f, w);
   |         ^
   = note: expected fn pointer `fn(i32)`
                 found fn item `fn(u32) {f}`
note: expected struct `Wrapper`, found a different struct `Wrapper`
  --> $DIR/two-mismatch-notes.rs:10:12
   |
LL |     foo(f, w);
   |            ^
   = note: expected struct `Wrapper<i32>`
              found struct `Wrapper<isize>`
note: function defined here
  --> $DIR/two-mismatch-notes.rs:4:4
   |
LL | fn foo(_: fn(i32), _: Wrapper<i32>) {}
   |    ^^^ ----------  ---------------

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
```

Yeah, it's a bit verbose, but much clearer IMO.

---

Open to discussions about how this could be further improved. Motivated by `@jyn514's` [tweet](https://mobile.twitter.com/joshuayn514/status/1558042020601634816) here.

Author: compiler-errors

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

@@ -1424,7 +1424,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// E0271, like `src/test/ui/issues/issue-39970.stderr`.
     #[tracing::instrument(
         level = "debug",
-        skip(self, diag, secondary_span, swap_secondary_and_primary, force_label)
+        skip(self, diag, secondary_span, swap_secondary_and_primary, prefer_label)
     )]
     pub fn note_type_err(
         &self,
@@ -1434,7 +1434,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         mut values: Option<ValuePairs<'tcx>>,
         terr: &TypeError<'tcx>,
         swap_secondary_and_primary: bool,
-        force_label: bool,
+        prefer_label: bool,
     ) {
         let span = cause.span();
 
@@ -1612,7 +1612,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             TypeError::ObjectUnsafeCoercion(_) => {}
             _ => {
                 let mut label_or_note = |span: Span, msg: &str| {
-                    if force_label || &[span] == diag.span.primary_spans() {
+                    if (prefer_label && is_simple_error) || &[span] == diag.span.primary_spans() {
                         diag.span_label(span, msg);
                     } else {
                         diag.span_note(span, msg);

compiler/rustc_typeck/src/check/fn_ctxt/checks.rs

@@ -544,7 +544,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let coerced_ty = expectation.only_has_type(self).unwrap_or(formal_input_ty);
             let can_coerce = self.can_coerce(arg_ty, coerced_ty);
             if !can_coerce {
-                return Compatibility::Incompatible(None);
+                return Compatibility::Incompatible(Some(ty::error::TypeError::Sorts(
+                    ty::error::ExpectedFound::new(true, coerced_ty, arg_ty),
+                )));
             }
 
             // Using probe here, since we don't want this subtyping to affect inference.

src/test/ui/argument-suggestions/issue-96638.stderr

@@ -2,7 +2,9 @@ error[E0061]: this function takes 3 arguments but 2 arguments were supplied
   --> $DIR/issue-96638.rs:8:5
    |
 LL |     f(&x, "");
-   |     ^ -- an argument of type `usize` is missing
+   |     ^ --  -- expected `usize`, found `&str`
+   |       |
+   |       an argument of type `usize` is missing
    |
 note: function defined here
   --> $DIR/issue-96638.rs:1:4

src/test/ui/argument-suggestions/issue-97484.stderr

@@ -2,8 +2,9 @@ error[E0061]: this function takes 4 arguments but 7 arguments were supplied
   --> $DIR/issue-97484.rs:12:5
    |
 LL |     foo(&&A, B, C, D, E, F, G);
-   |     ^^^      -  -        - argument of type `F` unexpected
-   |              |  |
+   |     ^^^      -  -     -  - argument of type `F` unexpected
+   |              |  |     |
+   |              |  |     expected `&E`, found struct `E`
    |              |  argument of type `C` unexpected
    |              argument of type `B` unexpected
    |

src/test/ui/argument-suggestions/two-mismatch-notes.rs

@@ -0,0 +1,11 @@
+#[derive(Copy, Clone)]
+struct Wrapper<T>(T);
+
+fn foo(_: fn(i32), _: Wrapper<i32>) {}
+
+fn f(_: u32) {}
+
+fn main() {
+    let w = Wrapper::<isize>(1isize);
+    foo(f, w); //~ ERROR arguments to this function are incorrect
+}

src/test/ui/argument-suggestions/two-mismatch-notes.stderr

@@ -0,0 +1,29 @@
+error[E0308]: arguments to this function are incorrect
+  --> $DIR/two-mismatch-notes.rs:10:5
+   |
+LL |     foo(f, w);
+   |     ^^^
+   |
+note: expected `i32`, found `u32`
+  --> $DIR/two-mismatch-notes.rs:10:9
+   |
+LL |     foo(f, w);
+   |         ^
+   = note: expected fn pointer `fn(i32)`
+                 found fn item `fn(u32) {f}`
+note: expected `i32`, found `isize`
+  --> $DIR/two-mismatch-notes.rs:10:12
+   |
+LL |     foo(f, w);
+   |            ^
+   = note: expected struct `Wrapper<i32>`
+              found struct `Wrapper<isize>`
+note: function defined here
+  --> $DIR/two-mismatch-notes.rs:4:4
+   |
+LL | fn foo(_: fn(i32), _: Wrapper<i32>) {}
+   |    ^^^ ----------  ---------------
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/issues/issue-18819.stderr

@@ -2,11 +2,13 @@ error[E0061]: this function takes 2 arguments but 1 argument was supplied
   --> $DIR/issue-18819.rs:16:5
    |
 LL |     print_x(X);
-   |     ^^^^^^^---
-   |            ||
-   |            |expected reference, found struct `X`
-   |            an argument of type `&str` is missing
+   |     ^^^^^^^--- an argument of type `&str` is missing
    |
+note: expected reference, found struct `X`
+  --> $DIR/issue-18819.rs:16:13
+   |
+LL |     print_x(X);
+   |             ^
    = note: expected reference `&dyn Foo<Item = bool>`
                  found struct `X`
 note: function defined here

src/test/ui/suggestions/args-instead-of-tuple-errors.stderr

@@ -2,10 +2,13 @@ error[E0061]: this enum variant takes 1 argument but 2 arguments were supplied
   --> $DIR/args-instead-of-tuple-errors.rs:6:34
    |
 LL |     let _: Option<(i32, bool)> = Some(1, 2);
-   |                                  ^^^^ -  - argument of type `{integer}` unexpected
-   |                                       |
-   |                                       expected tuple, found integer
+   |                                  ^^^^    - argument of type `{integer}` unexpected
    |
+note: expected tuple, found integer
+  --> $DIR/args-instead-of-tuple-errors.rs:6:39
+   |
+LL |     let _: Option<(i32, bool)> = Some(1, 2);
+   |                                       ^
    = note: expected tuple `(i32, bool)`
                found type `{integer}`
 note: tuple variant defined here
@@ -22,10 +25,13 @@ error[E0061]: this function takes 1 argument but 2 arguments were supplied
   --> $DIR/args-instead-of-tuple-errors.rs:8:5
    |
 LL |     int_bool(1, 2);
-   |     ^^^^^^^^ -  - argument of type `{integer}` unexpected
-   |              |
-   |              expected tuple, found integer
+   |     ^^^^^^^^    - argument of type `{integer}` unexpected
    |
+note: expected tuple, found integer
+  --> $DIR/args-instead-of-tuple-errors.rs:8:14
+   |
+LL |     int_bool(1, 2);
+   |              ^
    = note: expected tuple `(i32, bool)`
                found type `{integer}`
 note: function defined here

src/test/ui/tuple/wrong_argument_ice-3.stderr

@@ -2,10 +2,13 @@ error[E0061]: this function takes 1 argument but 2 arguments were supplied
   --> $DIR/wrong_argument_ice-3.rs:9:16
    |
 LL |         groups.push(new_group, vec![process]);
-   |                ^^^^ ---------  ------------- argument of type `Vec<&Process>` unexpected
-   |                     |
-   |                     expected tuple, found struct `Vec`
+   |                ^^^^            ------------- argument of type `Vec<&Process>` unexpected
    |
+note: expected tuple, found struct `Vec`
+  --> $DIR/wrong_argument_ice-3.rs:9:21
+   |
+LL |         groups.push(new_group, vec![process]);
+   |                     ^^^^^^^^^
    = note: expected tuple `(Vec<String>, Vec<Process>)`
              found struct `Vec<String>`
 note: associated function defined here