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
```

6 files changed, 106 insertions, 5 deletions

diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 23f29a24fe7..45c017df918 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -12,6 +12,7 @@ use rustc_span::{Span, DUMMY_SP};
 use std::borrow::Cow;
 use std::fmt;
 use std::hash::{Hash, Hasher};
+use std::panic::Location;
 
 /// Error type for `Diagnostic`'s `suggestions` field, indicating that
 /// `.disable_suggestions()` was called on the `Diagnostic`.
@@ -107,6 +108,31 @@ pub struct Diagnostic {
     /// If diagnostic is from Lint, custom hash function ignores notes
     /// otherwise hash is based on the all the fields
     pub is_lint: bool,
+
+    /// With `-Ztrack_diagnostics` enabled,
+    /// we print where in rustc this error was emitted.
+    pub emitted_at: DiagnosticLocation,
+}
+
+#[derive(Clone, Debug, Encodable, Decodable)]
+pub struct DiagnosticLocation {
+    file: Cow<'static, str>,
+    line: u32,
+    col: u32,
+}
+
+impl DiagnosticLocation {
+    #[track_caller]
+    fn caller() -> Self {
+        let loc = Location::caller();
+        DiagnosticLocation { file: loc.file().into(), line: loc.line(), col: loc.column() }
+    }
+}
+
+impl fmt::Display for DiagnosticLocation {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}:{}:{}", self.file, self.line, self.col)
+    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
@@ -173,10 +199,12 @@ impl StringPart {
 }
 
 impl Diagnostic {
+    #[track_caller]
     pub fn new<M: Into<DiagnosticMessage>>(level: Level, message: M) -> Self {
         Diagnostic::new_with_code(level, None, message)
     }
 
+    #[track_caller]
     pub fn new_with_code<M: Into<DiagnosticMessage>>(
         level: Level,
         code: Option<DiagnosticId>,
@@ -192,6 +220,7 @@ impl Diagnostic {
             args: Default::default(),
             sort_span: DUMMY_SP,
             is_lint: false,
+            emitted_at: DiagnosticLocation::caller(),
         }
     }
 
diff --git a/compiler/rustc_errors/src/diagnostic_builder.rs b/compiler/rustc_errors/src/diagnostic_builder.rs
index 9b41234dcfb..ecf8570e81f 100644
--- a/compiler/rustc_errors/src/diagnostic_builder.rs
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@@ -133,6 +133,7 @@ mod sealed_level_is_error {
 impl<'a> DiagnosticBuilder<'a, ErrorGuaranteed> {
     /// Convenience function for internal use, clients should use one of the
     /// `struct_*` methods on [`Handler`].
+    #[track_caller]
     pub(crate) fn new_guaranteeing_error<M: Into<DiagnosticMessage>, const L: Level>(
         handler: &'a Handler,
         message: M,
@@ -196,6 +197,7 @@ impl EmissionGuarantee for ErrorGuaranteed {
         }
     }
 
+    #[track_caller]
     fn make_diagnostic_builder(
         handler: &Handler,
         msg: impl Into<DiagnosticMessage>,
@@ -209,6 +211,7 @@ impl EmissionGuarantee for ErrorGuaranteed {
 impl<'a> DiagnosticBuilder<'a, ()> {
     /// Convenience function for internal use, clients should use one of the
     /// `struct_*` methods on [`Handler`].
+    #[track_caller]
     pub(crate) fn new<M: Into<DiagnosticMessage>>(
         handler: &'a Handler,
         level: Level,
@@ -220,6 +223,7 @@ impl<'a> DiagnosticBuilder<'a, ()> {
 
     /// Creates a new `DiagnosticBuilder` with an already constructed
     /// diagnostic.
+    #[track_caller]
     pub(crate) fn new_diagnostic(handler: &'a Handler, diagnostic: Diagnostic) -> Self {
         debug!("Created new diagnostic");
         Self {
@@ -308,6 +312,7 @@ impl EmissionGuarantee for Noted {
 impl<'a> DiagnosticBuilder<'a, !> {
     /// Convenience function for internal use, clients should use one of the
     /// `struct_*` methods on [`Handler`].
+    #[track_caller]
     pub(crate) fn new_fatal(handler: &'a Handler, message: impl Into<DiagnosticMessage>) -> Self {
         let diagnostic = Diagnostic::new_with_code(Level::Fatal, None, message);
         Self::new_diagnostic_fatal(handler, diagnostic)
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index cd6413bc3ec..b7b8fe3f25a 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -16,10 +16,10 @@ use crate::snippet::{Annotation, AnnotationType, Line, MultilineAnnotation, Styl
 use crate::styled_buffer::StyledBuffer;
 use crate::translation::{to_fluent_args, Translate};
 use crate::{
-    CodeSuggestion, Diagnostic, DiagnosticId, DiagnosticMessage, FluentBundle, Handler,
-    LazyFallbackBundle, Level, MultiSpan, SubDiagnostic, SubstitutionHighlight, SuggestionStyle,
+    diagnostic::DiagnosticLocation, CodeSuggestion, Diagnostic, DiagnosticId, DiagnosticMessage,
+    FluentBundle, Handler, LazyFallbackBundle, Level, MultiSpan, SubDiagnostic,
+    SubstitutionHighlight, SuggestionStyle,
 };
-
 use rustc_lint_defs::pluralize;
 
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
@@ -64,6 +64,7 @@ impl HumanReadableErrorType {
         teach: bool,
         diagnostic_width: Option<usize>,
         macro_backtrace: bool,
+        track_diagnostics: bool,
     ) -> EmitterWriter {
         let (short, color_config) = self.unzip();
         let color = color_config.suggests_using_colors();
@@ -77,6 +78,7 @@ impl HumanReadableErrorType {
             color,
             diagnostic_width,
             macro_backtrace,
+            track_diagnostics,
         )
     }
 }
@@ -557,6 +559,7 @@ impl Emitter for EmitterWriter {
             &primary_span,
             &children,
             &suggestions,
+            self.track_diagnostics.then_some(&diag.emitted_at),
         );
     }
 
@@ -650,6 +653,7 @@ pub struct EmitterWriter {
     diagnostic_width: Option<usize>,
 
     macro_backtrace: bool,
+    track_diagnostics: bool,
 }
 
 #[derive(Debug)]
@@ -669,6 +673,7 @@ impl EmitterWriter {
         teach: bool,
         diagnostic_width: Option<usize>,
         macro_backtrace: bool,
+        track_diagnostics: bool,
     ) -> EmitterWriter {
         let dst = Destination::from_stderr(color_config);
         EmitterWriter {
@@ -681,6 +686,7 @@ impl EmitterWriter {
             ui_testing: false,
             diagnostic_width,
             macro_backtrace,
+            track_diagnostics,
         }
     }
 
@@ -694,6 +700,7 @@ impl EmitterWriter {
         colored: bool,
         diagnostic_width: Option<usize>,
         macro_backtrace: bool,
+        track_diagnostics: bool,
     ) -> EmitterWriter {
         EmitterWriter {
             dst: Raw(dst, colored),
@@ -705,6 +712,7 @@ impl EmitterWriter {
             ui_testing: false,
             diagnostic_width,
             macro_backtrace,
+            track_diagnostics,
         }
     }
 
@@ -1327,6 +1335,7 @@ impl EmitterWriter {
         level: &Level,
         max_line_num_len: usize,
         is_secondary: bool,
+        emitted_at: Option<&DiagnosticLocation>,
     ) -> io::Result<()> {
         let mut buffer = StyledBuffer::new();
 
@@ -1377,7 +1386,6 @@ impl EmitterWriter {
                 }
             }
         }
-
         let mut annotated_files = FileWithAnnotatedLines::collect_annotations(self, args, msp);
 
         // Make sure our primary file comes first
@@ -1653,6 +1661,12 @@ impl EmitterWriter {
             }
         }
 
+        if let Some(tracked) = emitted_at {
+            let track = format!("-Ztrack-diagnostics: created at {tracked}");
+            let len = buffer.num_lines();
+            buffer.append(len, &track, Style::NoStyle);
+        }
+
         // final step: take our styled buffer, render it, then output it
         emit_to_destination(&buffer.render(), level, &mut self.dst, self.short_message)?;
 
@@ -1977,6 +1991,7 @@ impl EmitterWriter {
         span: &MultiSpan,
         children: &[SubDiagnostic],
         suggestions: &[CodeSuggestion],
+        emitted_at: Option<&DiagnosticLocation>,
     ) {
         let max_line_num_len = if self.ui_testing {
             ANONYMIZED_LINE_NUM.len()
@@ -1985,7 +2000,16 @@ impl EmitterWriter {
             num_decimal_digits(n)
         };
 
-        match self.emit_message_default(span, message, args, code, level, max_line_num_len, false) {
+        match self.emit_message_default(
+            span,
+            message,
+            args,
+            code,
+            level,
+            max_line_num_len,
+            false,
+            emitted_at,
+        ) {
             Ok(()) => {
                 if !children.is_empty()
                     || suggestions.iter().any(|s| s.style != SuggestionStyle::CompletelyHidden)
@@ -2014,6 +2038,7 @@ impl EmitterWriter {
                             &child.level,
                             max_line_num_len,
                             true,
+                            None,
                         ) {
                             panic!("failed to emit error: {}", err);
                         }
@@ -2030,6 +2055,7 @@ impl EmitterWriter {
                                 &Level::Help,
                                 max_line_num_len,
                                 true,
+                                None,
                             ) {
                                 panic!("failed to emit error: {}", e);
                             }
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index 4cc7be47fc2..c4498eafa4e 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -45,6 +45,7 @@ pub struct JsonEmitter {
     json_rendered: HumanReadableErrorType,
     diagnostic_width: Option<usize>,
     macro_backtrace: bool,
+    track_diagnostics: bool,
 }
 
 impl JsonEmitter {
@@ -57,6 +58,7 @@ impl JsonEmitter {
         json_rendered: HumanReadableErrorType,
         diagnostic_width: Option<usize>,
         macro_backtrace: bool,
+        track_diagnostics: bool,
     ) -> JsonEmitter {
         JsonEmitter {
             dst: Box::new(io::BufWriter::new(io::stderr())),
@@ -69,6 +71,7 @@ impl JsonEmitter {
             json_rendered,
             diagnostic_width,
             macro_backtrace,
+            track_diagnostics,
         }
     }
 
@@ -79,6 +82,7 @@ impl JsonEmitter {
         fallback_bundle: LazyFallbackBundle,
         diagnostic_width: Option<usize>,
         macro_backtrace: bool,
+        track_diagnostics: bool,
     ) -> JsonEmitter {
         let file_path_mapping = FilePathMapping::empty();
         JsonEmitter::stderr(
@@ -90,6 +94,7 @@ impl JsonEmitter {
             json_rendered,
             diagnostic_width,
             macro_backtrace,
+            track_diagnostics,
         )
     }
 
@@ -103,6 +108,7 @@ impl JsonEmitter {
         json_rendered: HumanReadableErrorType,
         diagnostic_width: Option<usize>,
         macro_backtrace: bool,
+        track_diagnostics: bool,
     ) -> JsonEmitter {
         JsonEmitter {
             dst,
@@ -115,6 +121,7 @@ impl JsonEmitter {
             json_rendered,
             diagnostic_width,
             macro_backtrace,
+            track_diagnostics,
         }
     }
 
@@ -350,6 +357,7 @@ impl Diagnostic {
                 false,
                 je.diagnostic_width,
                 je.macro_backtrace,
+                je.track_diagnostics,
             )
             .ui_testing(je.ui_testing)
             .emit_diagnostic(diag);
diff --git a/compiler/rustc_errors/src/json/tests.rs b/compiler/rustc_errors/src/json/tests.rs
index d940d14e1db..f131468971b 100644
--- a/compiler/rustc_errors/src/json/tests.rs
+++ b/compiler/rustc_errors/src/json/tests.rs
@@ -59,6 +59,7 @@ fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
             HumanReadableErrorType::Short(ColorConfig::Never),
             None,
             false,
+            false,
         );
 
         let span = Span::with_root_ctxt(BytePos(span.0), BytePos(span.1));
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 0963ea71f80..f390495b53d 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -492,6 +492,8 @@ pub struct HandlerFlags {
     pub macro_backtrace: bool,
     /// If true, identical diagnostics are reported only once.
     pub deduplicate_diagnostics: bool,
+    /// Track where errors are created. Enabled with `-Ztrack-diagnostics`.
+    pub track_diagnostics: bool,
 }
 
 impl Drop for HandlerInner {
@@ -559,6 +561,7 @@ impl Handler {
             false,
             None,
             flags.macro_backtrace,
+            flags.track_diagnostics,
         ));
         Self::with_emitter_and_flags(emitter, flags)
     }
@@ -664,6 +667,7 @@ impl Handler {
 
     /// Construct a builder with the `msg` at the level appropriate for the specific `EmissionGuarantee`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_diagnostic<G: EmissionGuarantee>(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -677,6 +681,7 @@ impl Handler {
     /// * `can_emit_warnings` is `true`
     /// * `is_force_warn` was set in `DiagnosticId::Lint`
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_warn(
         &self,
         span: impl Into<MultiSpan>,
@@ -693,6 +698,7 @@ impl Handler {
     /// Attempting to `.emit()` the builder will only emit if either:
     /// * `can_emit_warnings` is `true`
     /// * `is_force_warn` was set in `DiagnosticId::Lint`
+    #[track_caller]
     pub fn struct_span_warn_with_expectation(
         &self,
         span: impl Into<MultiSpan>,
@@ -706,6 +712,7 @@ impl Handler {
 
     /// Construct a builder at the `Allow` level at the given `span` and with the `msg`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_allow(
         &self,
         span: impl Into<MultiSpan>,
@@ -719,6 +726,7 @@ impl Handler {
     /// Construct a builder at the `Warning` level at the given `span` and with the `msg`.
     /// Also include a code.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_warn_with_code(
         &self,
         span: impl Into<MultiSpan>,
@@ -736,6 +744,7 @@ impl Handler {
     /// * `can_emit_warnings` is `true`
     /// * `is_force_warn` was set in `DiagnosticId::Lint`
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_warn(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
         DiagnosticBuilder::new(self, Level::Warning(None), msg)
     }
@@ -746,6 +755,7 @@ impl Handler {
     /// Attempting to `.emit()` the builder will only emit if either:
     /// * `can_emit_warnings` is `true`
     /// * `is_force_warn` was set in `DiagnosticId::Lint`
+    #[track_caller]
     pub fn struct_warn_with_expectation(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -756,12 +766,14 @@ impl Handler {
 
     /// Construct a builder at the `Allow` level with the `msg`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_allow(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
         DiagnosticBuilder::new(self, Level::Allow, msg)
     }
 
     /// Construct a builder at the `Expect` level with the `msg`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_expect(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -772,6 +784,7 @@ impl Handler {
 
     /// Construct a builder at the `Error` level at the given `span` and with the `msg`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_err(
         &self,
         span: impl Into<MultiSpan>,
@@ -784,6 +797,7 @@ impl Handler {
 
     /// Construct a builder at the `Error` level at the given `span`, with the `msg`, and `code`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_err_with_code(
         &self,
         span: impl Into<MultiSpan>,
@@ -798,6 +812,7 @@ impl Handler {
     /// Construct a builder at the `Error` level with the `msg`.
     // 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>,
@@ -807,12 +822,14 @@ impl Handler {
 
     /// This should only be used by `rustc_middle::lint::struct_lint_level`. Do not use it for hard errors.
     #[doc(hidden)]
+    #[track_caller]
     pub fn struct_err_lint(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
         DiagnosticBuilder::new(self, Level::Error { lint: true }, msg)
     }
 
     /// Construct a builder at the `Error` level with the `msg` and the `code`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_err_with_code(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -825,6 +842,7 @@ impl Handler {
 
     /// Construct a builder at the `Warn` level with the `msg` and the `code`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_warn_with_code(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -837,6 +855,7 @@ impl Handler {
 
     /// Construct a builder at the `Fatal` level at the given `span` and with the `msg`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_fatal(
         &self,
         span: impl Into<MultiSpan>,
@@ -849,6 +868,7 @@ impl Handler {
 
     /// Construct a builder at the `Fatal` level at the given `span`, with the `msg`, and `code`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_fatal_with_code(
         &self,
         span: impl Into<MultiSpan>,
@@ -862,6 +882,7 @@ impl Handler {
 
     /// Construct a builder at the `Error` level with the `msg`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_fatal(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, !> {
         DiagnosticBuilder::new_fatal(self, msg)
     }
@@ -874,6 +895,7 @@ impl Handler {
 
     /// Construct a builder at the `Note` level with the `msg`.
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_note_without_error(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -882,12 +904,14 @@ impl Handler {
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_fatal(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) -> ! {
         self.emit_diag_at_span(Diagnostic::new(Fatal, msg), span);
         FatalError.raise()
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_fatal_with_code(
         &self,
         span: impl Into<MultiSpan>,
@@ -899,6 +923,7 @@ impl Handler {
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_err(
         &self,
         span: impl Into<MultiSpan>,
@@ -908,6 +933,7 @@ impl Handler {
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_err_with_code(
         &self,
         span: impl Into<MultiSpan>,
@@ -921,11 +947,13 @@ impl Handler {
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_warn(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) {
         self.emit_diag_at_span(Diagnostic::new(Warning(None), msg), span);
     }
 
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn span_warn_with_code(
         &self,
         span: impl Into<MultiSpan>,
@@ -954,10 +982,12 @@ impl Handler {
         self.inner.borrow_mut().delay_good_path_bug(msg)
     }
 
+    #[track_caller]
     pub fn span_bug_no_panic(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) {
         self.emit_diag_at_span(Diagnostic::new(Bug, msg), span);
     }
 
+    #[track_caller]
     pub fn span_note_without_error(
         &self,
         span: impl Into<MultiSpan>,
@@ -966,6 +996,7 @@ impl Handler {
         self.emit_diag_at_span(Diagnostic::new(Note, msg), span);
     }
 
+    #[track_caller]
     pub fn span_note_diag(
         &self,
         span: Span,
@@ -1452,6 +1483,7 @@ impl HandlerInner {
         }
     }
 
+    #[track_caller]
     fn span_bug(&mut self, sp: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) -> ! {
         self.emit_diag_at_span(Diagnostic::new(Bug, msg), sp);
         panic::panic_any(ExplicitBug);