Auto merge of rust-lang#103217 - mejrs:track, r=eholk

Track where diagnostics were created.

This implements the `-Ztrack-diagnostics` flag, which uses `#[track_caller]` to track where diagnostics are created. It is meant as a debugging tool much like `-Ztreat-err-as-bug`.

For example, the following code...

```rust
struct A;
struct B;

fn main(){
    let _: A = B;
}
```
...now emits the following error message:

```
error[E0308]: mismatched types
 --> src\main.rs:5:16
  |
5 |     let _: A = B;
  |            -   ^ expected struct `A`, found struct `B`
  |            |
  |            expected due to this
-Ztrack-diagnostics: created at compiler\rustc_infer\src\infer\error_reporting\mod.rs:2275:31
```

Author: bors

clippy_lints/src/doc.rs

@@ -691,6 +691,7 @@ fn check_code(cx: &LateContext<'_>, text: &str, edition: Edition, span: Span) {
                     false,
                     None,
                     false,
+                    false,
                 );
                 let handler = Handler::with_emitter(false, None, Box::new(emitter));
                 let sess = ParseSess::with_span_handler(handler, sm);

src/driver.rs

@@ -179,6 +179,7 @@ fn report_clippy_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str) {
         false,
         None,
         false,
+        false,
     ));
     let handler = rustc_errors::Handler::with_emitter(true, None, emitter);
 

tests/ui/track-diagnostics.rs

@@ -0,0 +1,12 @@
+// compile-flags: -Z track-diagnostics
+// error-pattern: created at
+
+// Normalize the emitted location so this doesn't need
+// updating everytime someone adds or removes a line.
+// normalize-stderr-test ".rs:\d+:\d+" -> ".rs:LL:CC"
+
+struct A;
+struct B;
+const S: A = B;
+
+fn main() {}

tests/ui/track-diagnostics.stderr

@@ -0,0 +1,10 @@
+error[E0308]: mismatched types
+  --> $DIR/track-diagnostics.rs:LL:CC
+   |
+LL | const S: A = B;
+   |              ^ expected struct `A`, found struct `B`
+-Ztrack-diagnostics: created at compiler/rustc_infer/src/infer/error_reporting/mod.rs:LL:CC
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.