Auto merge of #36338 - estebank:primitive-shadow, r=jseyfried

Be more specific when type parameter shadows primitive type

When a type parameter shadows a primitive type, the error message
was non obvious. For example, given the file `file.rs`:

```rust
trait Parser<T> {
    fn parse(text: &str) -> Option<T>;
}

impl<bool> Parser<bool> for bool {
    fn parse(text: &str) -> Option<bool> {
        Some(true)
    }
}

fn main() {
    println!("{}", bool::parse("ok").unwrap_or(false));
}
```

The output was:

```bash
% rustc file.rs
error[E0308]: mismatched types
 --> file.rs:7:14
  |
7 |         Some(true)
  |              ^^^^ expected type parameter, found bool a
  |
  = note: expected type `bool`
  = note:    found type `bool`

error: aborting due to previous error
```

We now show extra information about the type:

```bash
% rustc file.rs
error[E0308]: mismatched types
 --> file.rs:7:14
  |
7 |         Some(true)
  |              ^^^^ expected type parameter, found bool a
  |
  = note: expected type `bool` (type parameter)
  = note:    found type `bool` (bool)

error: aborting due to previous error
```

Fixes #35030

1 files changed, 14 insertions, 3 deletions

diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index d82d7dbe70f..d2f3eea85f2 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -274,9 +274,20 @@ impl<'a> DiagnosticBuilder<'a> {
                                found: &fmt::Display)
                                -> &mut DiagnosticBuilder<'a>
     {
+        self.note_expected_found_extra(label, expected, found, &"", &"")
+    }
+
+    pub fn note_expected_found_extra(&mut self,
+                                     label: &fmt::Display,
+                                     expected: &fmt::Display,
+                                     found: &fmt::Display,
+                                     expected_extra: &fmt::Display,
+                                     found_extra: &fmt::Display)
+                                     -> &mut DiagnosticBuilder<'a>
+    {
         // For now, just attach these as notes
-        self.note(&format!("expected {} `{}`", label, expected));
-        self.note(&format!("   found {} `{}`", label, found));
+        self.note(&format!("expected {} `{}`{}", label, expected, expected_extra));
+        self.note(&format!("   found {} `{}`{}", label, found, found_extra));
         self
     }
 
@@ -764,4 +775,4 @@ pub fn expect<T, M>(diag: &Handler, opt: Option<T>, msg: M) -> T where
         Some(t) => t,
         None => diag.bug(&msg()),
     }
-}
\ No newline at end of file
+}