1 files changed, 215 insertions, 0 deletions
diff --git a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
new file mode 100644
index 000000000..0fcd61d1e
--- /dev/null
+++ b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
@@ -0,0 +1,215 @@
+//! Emit diagnostics using the `annotate-snippets` library
+//!
+//! This is the equivalent of `./emitter.rs` but making use of the
+//! [`annotate-snippets`][annotate_snippets] library instead of building the output ourselves.
+//!
+//! [annotate_snippets]: https://docs.rs/crate/annotate-snippets/
+
+use crate::emitter::FileWithAnnotatedLines;
+use crate::snippet::Line;
+use crate::{
+    CodeSuggestion, Diagnostic, DiagnosticId, DiagnosticMessage, Emitter, FluentBundle,
+    LazyFallbackBundle, Level, MultiSpan, Style, SubDiagnostic,
+};
+use annotate_snippets::display_list::{DisplayList, FormatOptions};
+use annotate_snippets::snippet::*;
+use rustc_data_structures::sync::Lrc;
+use rustc_error_messages::FluentArgs;
+use rustc_span::source_map::SourceMap;
+use rustc_span::SourceFile;
+
+/// Generates diagnostics using annotate-snippet
+pub struct AnnotateSnippetEmitterWriter {
+    source_map: Option<Lrc<SourceMap>>,
+    fluent_bundle: Option<Lrc<FluentBundle>>,
+    fallback_bundle: LazyFallbackBundle,
+
+    /// If true, hides the longer explanation text
+    short_message: bool,
+    /// If true, will normalize line numbers with `LL` to prevent noise in UI test diffs.
+    ui_testing: bool,
+
+    macro_backtrace: bool,
+}
+
+impl Emitter for AnnotateSnippetEmitterWriter {
+    /// The entry point for the diagnostics generation
+    fn emit_diagnostic(&mut self, diag: &Diagnostic) {
+        let fluent_args = self.to_fluent_args(diag.args());
+
+        let mut children = diag.children.clone();
+        let (mut primary_span, suggestions) = self.primary_span_formatted(&diag, &fluent_args);
+
+        self.fix_multispans_in_extern_macros_and_render_macro_backtrace(
+            &self.source_map,
+            &mut primary_span,
+            &mut children,
+            &diag.level,
+            self.macro_backtrace,
+        );
+
+        self.emit_messages_default(
+            &diag.level,
+            &diag.message,
+            &fluent_args,
+            &diag.code,
+            &primary_span,
+            &children,
+            &suggestions,
+        );
+    }
+
+    fn source_map(&self) -> Option<&Lrc<SourceMap>> {
+        self.source_map.as_ref()
+    }
+
+    fn fluent_bundle(&self) -> Option<&Lrc<FluentBundle>> {
+        self.fluent_bundle.as_ref()
+    }
+
+    fn fallback_fluent_bundle(&self) -> &FluentBundle {
+        &**self.fallback_bundle
+    }
+
+    fn should_show_explain(&self) -> bool {
+        !self.short_message
+    }
+}
+
+/// Provides the source string for the given `line` of `file`
+fn source_string(file: Lrc<SourceFile>, line: &Line) -> String {
+    file.get_line(line.line_index - 1).map(|a| a.to_string()).unwrap_or_default()
+}
+
+/// Maps `Diagnostic::Level` to `snippet::AnnotationType`
+fn annotation_type_for_level(level: Level) -> AnnotationType {
+    match level {
+        Level::Bug | Level::DelayedBug | Level::Fatal | Level::Error { .. } => {
+            AnnotationType::Error
+        }
+        Level::Warning(_) => AnnotationType::Warning,
+        Level::Note | Level::OnceNote => AnnotationType::Note,
+        Level::Help => AnnotationType::Help,
+        // FIXME(#59346): Not sure how to map this level
+        Level::FailureNote => AnnotationType::Error,
+        Level::Allow => panic!("Should not call with Allow"),
+        Level::Expect(_) => panic!("Should not call with Expect"),
+    }
+}
+
+impl AnnotateSnippetEmitterWriter {
+    pub fn new(
+        source_map: Option<Lrc<SourceMap>>,
+        fluent_bundle: Option<Lrc<FluentBundle>>,
+        fallback_bundle: LazyFallbackBundle,
+        short_message: bool,
+        macro_backtrace: bool,
+    ) -> Self {
+        Self {
+            source_map,
+            fluent_bundle,
+            fallback_bundle,
+            short_message,
+            ui_testing: false,
+            macro_backtrace,
+        }
+    }
+
+    /// Allows to modify `Self` to enable or disable the `ui_testing` flag.
+    ///
+    /// If this is set to true, line numbers will be normalized as `LL` in the output.
+    pub fn ui_testing(mut self, ui_testing: bool) -> Self {
+        self.ui_testing = ui_testing;
+        self
+    }
+
+    fn emit_messages_default(
+        &mut self,
+        level: &Level,
+        messages: &[(DiagnosticMessage, Style)],
+        args: &FluentArgs<'_>,
+        code: &Option<DiagnosticId>,
+        msp: &MultiSpan,
+        _children: &[SubDiagnostic],
+        _suggestions: &[CodeSuggestion],
+    ) {
+        let message = self.translate_messages(messages, args);
+        if let Some(source_map) = &self.source_map {
+            // Make sure our primary file comes first
+            let primary_lo = if let Some(ref primary_span) = msp.primary_span().as_ref() {
+                if primary_span.is_dummy() {
+                    // FIXME(#59346): Not sure when this is the case and what
+                    // should be done if it happens
+                    return;
+                } else {
+                    source_map.lookup_char_pos(primary_span.lo())
+                }
+            } else {
+                // FIXME(#59346): Not sure when this is the case and what
+                // should be done if it happens
+                return;
+            };
+            let mut annotated_files = FileWithAnnotatedLines::collect_annotations(self, args, msp);
+            if let Ok(pos) =
+                annotated_files.binary_search_by(|x| x.file.name.cmp(&primary_lo.file.name))
+            {
+                annotated_files.swap(0, pos);
+            }
+            // owned: line source, line index, annotations
+            type Owned = (String, usize, Vec<crate::snippet::Annotation>);
+            let filename = source_map.filename_for_diagnostics(&primary_lo.file.name);
+            let origin = filename.to_string_lossy();
+            let annotated_files: Vec<Owned> = annotated_files
+                .into_iter()
+                .flat_map(|annotated_file| {
+                    let file = annotated_file.file;
+                    annotated_file
+                        .lines
+                        .into_iter()
+                        .map(|line| {
+                            (source_string(file.clone(), &line), line.line_index, line.annotations)
+                        })
+                        .collect::<Vec<Owned>>()
+                })
+                .collect();
+            let snippet = Snippet {
+                title: Some(Annotation {
+                    label: Some(&message),
+                    id: code.as_ref().map(|c| match c {
+                        DiagnosticId::Error(val) | DiagnosticId::Lint { name: val, .. } => {
+                            val.as_str()
+                        }
+                    }),
+                    annotation_type: annotation_type_for_level(*level),
+                }),
+                footer: vec![],
+                opt: FormatOptions { color: true, anonymized_line_numbers: self.ui_testing },
+                slices: annotated_files
+                    .iter()
+                    .map(|(source, line_index, annotations)| {
+                        Slice {
+                            source,
+                            line_start: *line_index,
+                            origin: Some(&origin),
+                            // FIXME(#59346): Not really sure when `fold` should be true or false
+                            fold: false,
+                            annotations: annotations
+                                .iter()
+                                .map(|annotation| SourceAnnotation {
+                                    range: (annotation.start_col, annotation.end_col),
+                                    label: annotation.label.as_deref().unwrap_or_default(),
+                                    annotation_type: annotation_type_for_level(*level),
+                                })
+                                .collect(),
+                        }
+                    })
+                    .collect(),
+            };
+            // FIXME(#59346): Figure out if we can _always_ print to stderr or not.
+            // `emitter.rs` has the `Destination` enum that lists various possible output
+            // destinations.
+            eprintln!("{}", DisplayList::from(snippet))
+        }
+        // FIXME(#59346): Is it ok to return None if there's no source_map?
+    }
+}