Auto merge of #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
```

4 files changed, 51 insertions, 3 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index f2ee52262ad..856ff3d4150 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -794,6 +794,7 @@ impl UnstableOptions {
             report_delayed_bugs: self.report_delayed_bugs,
             macro_backtrace: self.macro_backtrace,
             deduplicate_diagnostics: self.deduplicate_diagnostics,
+            track_diagnostics: self.track_diagnostics,
         }
     }
 }
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 3f234a47a3d..e93c4138e61 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1587,6 +1587,8 @@ options! {
         "choose the TLS model to use (`rustc --print tls-models` for details)"),
     trace_macros: bool = (false, parse_bool, [UNTRACKED],
         "for every macro invocation, print its name and arguments (default: no)"),
+    track_diagnostics: bool = (false, parse_bool, [UNTRACKED],
+        "tracks where in rustc a diagnostic was emitted"),
     // Diagnostics are considered side-effects of a query (see `QuerySideEffects`) and are saved
     // alongside query results and changes to translation options can affect diagnostics - so
     // translation options should be tracked.
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index a199947ebed..f9f4f2979c4 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -97,6 +97,7 @@ pub fn feature_err<'a>(
 ///
 /// This variant allows you to control whether it is a library or language feature.
 /// Almost always, you want to use this for a language feature. If so, prefer `feature_err`.
+#[track_caller]
 pub fn feature_err_issue<'a>(
     sess: &'a ParseSess,
     feature: Symbol,
@@ -332,6 +333,7 @@ impl ParseSess {
         self.proc_macro_quoted_spans.lock().clone()
     }
 
+    #[track_caller]
     pub fn create_err<'a>(
         &'a self,
         err: impl IntoDiagnostic<'a>,
@@ -339,10 +341,12 @@ impl ParseSess {
         err.into_diagnostic(&self.span_diagnostic)
     }
 
+    #[track_caller]
     pub fn emit_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> ErrorGuaranteed {
         self.create_err(err).emit()
     }
 
+    #[track_caller]
     pub fn create_warning<'a>(
         &'a self,
         warning: impl IntoDiagnostic<'a, ()>,
@@ -350,6 +354,7 @@ impl ParseSess {
         warning.into_diagnostic(&self.span_diagnostic)
     }
 
+    #[track_caller]
     pub fn emit_warning<'a>(&'a self, warning: impl IntoDiagnostic<'a, ()>) {
         self.create_warning(warning).emit()
     }
@@ -377,6 +382,7 @@ impl ParseSess {
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_err(
         &self,
         msg: impl Into<DiagnosticMessage>,
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 100c66f6364..6d3cda684a6 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -286,6 +286,7 @@ impl Session {
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_warn<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -294,6 +295,7 @@ impl Session {
         self.diagnostic().struct_span_warn(sp, msg)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_warn_with_expectation<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -303,6 +305,7 @@ impl Session {
         self.diagnostic().struct_span_warn_with_expectation(sp, msg, id)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_warn_with_code<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -312,10 +315,12 @@ impl Session {
         self.diagnostic().struct_span_warn_with_code(sp, msg, code)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_warn(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
         self.diagnostic().struct_warn(msg)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_warn_with_expectation(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -324,6 +329,7 @@ impl Session {
         self.diagnostic().struct_warn_with_expectation(msg, id)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_allow<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -332,10 +338,12 @@ impl Session {
         self.diagnostic().struct_span_allow(sp, msg)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_allow(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
         self.diagnostic().struct_allow(msg)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_expect(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -344,6 +352,7 @@ impl Session {
         self.diagnostic().struct_expect(msg, id)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_err<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -352,6 +361,7 @@ impl Session {
         self.diagnostic().struct_span_err(sp, msg)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -362,12 +372,14 @@ impl Session {
     }
     // FIXME: This method should be removed (every error should have an associated error code).
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_err(
         &self,
         msg: impl Into<DiagnosticMessage>,
     ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
         self.parse_sess.struct_err(msg)
     }
+    #[track_caller]
     #[rustc_lint_diagnostics]
     pub fn struct_err_with_code(
         &self,
@@ -377,6 +389,7 @@ impl Session {
         self.diagnostic().struct_err_with_code(msg, code)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_warn_with_code(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -385,6 +398,7 @@ impl Session {
         self.diagnostic().struct_warn_with_code(msg, code)
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_fatal<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -407,6 +421,7 @@ impl Session {
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_fatal<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) -> ! {
         self.diagnostic().span_fatal(sp, msg)
     }
@@ -424,6 +439,7 @@ impl Session {
         self.diagnostic().fatal(msg).raise()
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_err_or_warn<S: Into<MultiSpan>>(
         &self,
         is_warning: bool,
@@ -437,6 +453,7 @@ impl Session {
         }
     }
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_err<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -457,12 +474,14 @@ impl Session {
     pub fn err(&self, msg: impl Into<DiagnosticMessage>) -> ErrorGuaranteed {
         self.diagnostic().err(msg)
     }
+    #[track_caller]
     pub fn create_err<'a>(
         &'a self,
         err: impl IntoDiagnostic<'a>,
     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
         self.parse_sess.create_err(err)
     }
+    #[track_caller]
     pub fn create_feature_err<'a>(
         &'a self,
         err: impl IntoDiagnostic<'a>,
@@ -475,33 +494,40 @@ impl Session {
         add_feature_diagnostics(&mut err, &self.parse_sess, feature);
         err
     }
+    #[track_caller]
     pub fn emit_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> ErrorGuaranteed {
         self.parse_sess.emit_err(err)
     }
+    #[track_caller]
     pub fn create_warning<'a>(
         &'a self,
         err: impl IntoDiagnostic<'a, ()>,
     ) -> DiagnosticBuilder<'a, ()> {
         self.parse_sess.create_warning(err)
     }
+    #[track_caller]
     pub fn emit_warning<'a>(&'a self, warning: impl IntoDiagnostic<'a, ()>) {
         self.parse_sess.emit_warning(warning)
     }
+    #[track_caller]
     pub fn create_note<'a>(
         &'a self,
         note: impl IntoDiagnostic<'a, Noted>,
     ) -> DiagnosticBuilder<'a, Noted> {
         self.parse_sess.create_note(note)
     }
+    #[track_caller]
     pub fn emit_note<'a>(&'a self, note: impl IntoDiagnostic<'a, Noted>) -> Noted {
         self.parse_sess.emit_note(note)
     }
+    #[track_caller]
     pub fn create_fatal<'a>(
         &'a self,
         fatal: impl IntoDiagnostic<'a, !>,
     ) -> DiagnosticBuilder<'a, !> {
         self.parse_sess.create_fatal(fatal)
     }
+    #[track_caller]
     pub fn emit_fatal<'a>(&'a self, fatal: impl IntoDiagnostic<'a, !>) -> ! {
         self.parse_sess.emit_fatal(fatal)
     }
@@ -541,6 +567,7 @@ impl Session {
     }
     #[allow(rustc::untranslatable_diagnostic)]
     #[allow(rustc::diagnostic_outside_of_impl)]
+    #[track_caller]
     pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) {
         self.diagnostic().span_warn(sp, msg)
     }
@@ -587,6 +614,8 @@ impl Session {
     pub fn note_without_error(&self, msg: impl Into<DiagnosticMessage>) {
         self.diagnostic().note_without_error(msg)
     }
+
+    #[track_caller]
     pub fn span_note_without_error<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -1213,6 +1242,7 @@ fn default_emitter(
     fallback_bundle: LazyFallbackBundle,
 ) -> Box<dyn Emitter + sync::Send> {
     let macro_backtrace = sopts.unstable_opts.macro_backtrace;
+    let track_diagnostics = sopts.unstable_opts.track_diagnostics;
     match sopts.error_format {
         config::ErrorOutputType::HumanReadable(kind) => {
             let (short, color_config) = kind.unzip();
@@ -1236,6 +1266,7 @@ fn default_emitter(
                     sopts.unstable_opts.teach,
                     sopts.diagnostic_width,
                     macro_backtrace,
+                    track_diagnostics,
                 );
                 Box::new(emitter.ui_testing(sopts.unstable_opts.ui_testing))
             }
@@ -1250,6 +1281,7 @@ fn default_emitter(
                 json_rendered,
                 sopts.diagnostic_width,
                 macro_backtrace,
+                track_diagnostics,
             )
             .ui_testing(sopts.unstable_opts.ui_testing),
         ),
@@ -1552,11 +1584,18 @@ fn early_error_handler(output: config::ErrorOutputType) -> rustc_errors::Handler
                 false,
                 None,
                 false,
+                false,
             ))
         }
-        config::ErrorOutputType::Json { pretty, json_rendered } => {
-            Box::new(JsonEmitter::basic(pretty, json_rendered, None, fallback_bundle, None, false))
-        }
+        config::ErrorOutputType::Json { pretty, json_rendered } => Box::new(JsonEmitter::basic(
+            pretty,
+            json_rendered,
+            None,
+            fallback_bundle,
+            None,
+            false,
+            false,
+        )),
     };
     rustc_errors::Handler::with_emitter(true, None, emitter)
 }