Merge pull request #19126 from lnicola/sync-from-rust

minor: Sync from downstream

6 files changed, 233 insertions, 171 deletions

diff --git a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
index b337e279400..f0636b600b7 100644
--- a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
+++ b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
@@ -5,8 +5,9 @@
 //!
 //! [annotate_snippets]: https://docs.rs/crate/annotate-snippets/
 
+use std::sync::Arc;
+
 use annotate_snippets::{Renderer, Snippet};
-use rustc_data_structures::sync::Lrc;
 use rustc_error_messages::FluentArgs;
 use rustc_span::SourceFile;
 use rustc_span::source_map::SourceMap;
@@ -22,8 +23,8 @@ use crate::{
 
 /// Generates diagnostics using annotate-snippet
 pub struct AnnotateSnippetEmitter {
-    source_map: Option<Lrc<SourceMap>>,
-    fluent_bundle: Option<Lrc<FluentBundle>>,
+    source_map: Option<Arc<SourceMap>>,
+    fluent_bundle: Option<Arc<FluentBundle>>,
     fallback_bundle: LazyFallbackBundle,
 
     /// If true, hides the longer explanation text
@@ -80,7 +81,7 @@ impl Emitter for AnnotateSnippetEmitter {
 }
 
 /// Provides the source string for the given `line` of `file`
-fn source_string(file: Lrc<SourceFile>, line: &Line) -> String {
+fn source_string(file: Arc<SourceFile>, line: &Line) -> String {
     file.get_line(line.line_index - 1).map(|a| a.to_string()).unwrap_or_default()
 }
 
@@ -102,8 +103,8 @@ fn annotation_level_for_level(level: Level) -> annotate_snippets::Level {
 
 impl AnnotateSnippetEmitter {
     pub fn new(
-        source_map: Option<Lrc<SourceMap>>,
-        fluent_bundle: Option<Lrc<FluentBundle>>,
+        source_map: Option<Arc<SourceMap>>,
+        fluent_bundle: Option<Arc<FluentBundle>>,
         fallback_bundle: LazyFallbackBundle,
         short_message: bool,
         macro_backtrace: bool,
@@ -174,7 +175,7 @@ impl AnnotateSnippetEmitter {
                             source_map.ensure_source_file_source_present(&file);
                             (
                                 format!("{}", source_map.filename_for_diagnostics(&file.name)),
-                                source_string(Lrc::clone(&file), &line),
+                                source_string(Arc::clone(&file), &line),
                                 line.line_index,
                                 line.annotations,
                             )
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 797dcd7b4d1..29a74ed3f4e 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -4,6 +4,7 @@ use std::hash::{Hash, Hasher};
 use std::marker::PhantomData;
 use std::ops::{Deref, DerefMut};
 use std::panic;
+use std::path::PathBuf;
 use std::thread::panicking;
 
 use rustc_data_structures::fx::FxIndexMap;
@@ -301,6 +302,7 @@ pub struct DiagInner {
 
     pub is_lint: Option<IsLint>,
 
+    pub long_ty_path: Option<PathBuf>,
     /// With `-Ztrack_diagnostics` enabled,
     /// we print where in rustc this error was emitted.
     pub(crate) emitted_at: DiagLocation,
@@ -324,6 +326,7 @@ impl DiagInner {
             args: Default::default(),
             sort_span: DUMMY_SP,
             is_lint: None,
+            long_ty_path: None,
             emitted_at: DiagLocation::caller(),
         }
     }
@@ -641,7 +644,14 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         found_label: &dyn fmt::Display,
         found: DiagStyledString,
     ) -> &mut Self {
-        self.note_expected_found_extra(expected_label, expected, found_label, found, &"", &"")
+        self.note_expected_found_extra(
+            expected_label,
+            expected,
+            found_label,
+            found,
+            DiagStyledString::normal(""),
+            DiagStyledString::normal(""),
+        )
     }
 
     #[rustc_lint_diagnostics]
@@ -651,8 +661,8 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         expected: DiagStyledString,
         found_label: &dyn fmt::Display,
         found: DiagStyledString,
-        expected_extra: &dyn fmt::Display,
-        found_extra: &dyn fmt::Display,
+        expected_extra: DiagStyledString,
+        found_extra: DiagStyledString,
     ) -> &mut Self {
         let expected_label = expected_label.to_string();
         let expected_label = if expected_label.is_empty() {
@@ -677,10 +687,13 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
             expected_label
         ))];
         msg.extend(expected.0);
-        msg.push(StringPart::normal(format!("`{expected_extra}\n")));
+        msg.push(StringPart::normal(format!("`")));
+        msg.extend(expected_extra.0);
+        msg.push(StringPart::normal(format!("\n")));
         msg.push(StringPart::normal(format!("{}{} `", " ".repeat(found_padding), found_label)));
         msg.extend(found.0);
-        msg.push(StringPart::normal(format!("`{found_extra}")));
+        msg.push(StringPart::normal(format!("`")));
+        msg.extend(found_extra.0);
 
         // For now, just attach these as notes.
         self.highlighted_note(msg);
@@ -1293,9 +1306,37 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
     /// `cancel`, etc. Afterwards, `drop` is the only code that will be run on
     /// `self`.
     fn take_diag(&mut self) -> DiagInner {
+        if let Some(path) = &self.long_ty_path {
+            self.note(format!(
+                "the full name for the type has been written to '{}'",
+                path.display()
+            ));
+            self.note("consider using `--verbose` to print the full type name to the console");
+        }
         Box::into_inner(self.diag.take().unwrap())
     }
 
+    /// This method allows us to access the path of the file where "long types" are written to.
+    ///
+    /// When calling `Diag::emit`, as part of that we will check if a `long_ty_path` has been set,
+    /// and if it has been then we add a note mentioning the file where the "long types" were
+    /// written to.
+    ///
+    /// When calling `tcx.short_string()` after a `Diag` is constructed, the preferred way of doing
+    /// so is `tcx.short_string(ty, diag.long_ty_path())`. The diagnostic itself is the one that
+    /// keeps the existence of a "long type" anywhere in the diagnostic, so the note telling the
+    /// user where we wrote the file to is only printed once at most, *and* it makes it much harder
+    /// to forget to set it.
+    ///
+    /// If the diagnostic hasn't been created before a "short ty string" is created, then you should
+    /// ensure that this method is called to set it `*diag.long_ty_path() = path`.
+    ///
+    /// As a rule of thumb, if you see or add at least one `tcx.short_string()` call anywhere, in a
+    /// scope, `diag.long_ty_path()` should be called once somewhere close by.
+    pub fn long_ty_path(&mut self) -> &mut Option<PathBuf> {
+        &mut self.long_ty_path
+    }
+
     /// Most `emit_producing_guarantee` functions use this as a starting point.
     fn emit_producing_nothing(mut self) {
         let diag = self.take_diag();
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index f938352820d..15cf285e7ff 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -14,10 +14,11 @@ use std::io::prelude::*;
 use std::io::{self, IsTerminal};
 use std::iter;
 use std::path::Path;
+use std::sync::Arc;
 
 use derive_setters::Setters;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
-use rustc_data_structures::sync::{DynSend, IntoDynSyncSend, Lrc};
+use rustc_data_structures::sync::{DynSend, IntoDynSyncSend};
 use rustc_error_messages::{FluentArgs, SpanLabel};
 use rustc_lexer;
 use rustc_lint_defs::pluralize;
@@ -35,8 +36,8 @@ use crate::snippet::{
 use crate::styled_buffer::StyledBuffer;
 use crate::translation::{Translate, to_fluent_args};
 use crate::{
-    CodeSuggestion, DiagCtxt, DiagInner, DiagMessage, ErrCode, FluentBundle, LazyFallbackBundle,
-    Level, MultiSpan, Subdiag, SubstitutionHighlight, SuggestionStyle, TerminalUrl,
+    CodeSuggestion, DiagInner, DiagMessage, ErrCode, FluentBundle, LazyFallbackBundle, Level,
+    MultiSpan, Subdiag, SubstitutionHighlight, SuggestionStyle, TerminalUrl,
 };
 
 /// Default column width, used in tests and when terminal dimensions cannot be determined.
@@ -537,11 +538,10 @@ impl Emitter for HumanEmitter {
 }
 
 /// An emitter that does nothing when emitting a non-fatal diagnostic.
-/// Fatal diagnostics are forwarded to `fatal_dcx` to avoid silent
+/// Fatal diagnostics are forwarded to `fatal_emitter` to avoid silent
 /// failures of rustc, as witnessed e.g. in issue #89358.
 pub struct SilentEmitter {
-    pub fallback_bundle: LazyFallbackBundle,
-    pub fatal_dcx: DiagCtxt,
+    pub fatal_emitter: Box<dyn Emitter + DynSend>,
     pub fatal_note: Option<String>,
     pub emit_fatal_diagnostic: bool,
 }
@@ -552,9 +552,7 @@ impl Translate for SilentEmitter {
     }
 
     fn fallback_fluent_bundle(&self) -> &FluentBundle {
-        // Ideally this field wouldn't be necessary and the fallback bundle in `fatal_dcx` would be
-        // used but the lock prevents this.
-        &self.fallback_bundle
+        self.fatal_emitter.fallback_fluent_bundle()
     }
 }
 
@@ -563,12 +561,12 @@ impl Emitter for SilentEmitter {
         None
     }
 
-    fn emit_diagnostic(&mut self, mut diag: DiagInner, _registry: &Registry) {
+    fn emit_diagnostic(&mut self, mut diag: DiagInner, registry: &Registry) {
         if self.emit_fatal_diagnostic && diag.level == Level::Fatal {
             if let Some(fatal_note) = &self.fatal_note {
                 diag.sub(Level::Note, fatal_note.clone(), MultiSpan::new());
             }
-            self.fatal_dcx.handle().emit_diagnostic(diag);
+            self.fatal_emitter.emit_diagnostic(diag, registry);
         }
     }
 }
@@ -613,8 +611,8 @@ pub enum OutputTheme {
 pub struct HumanEmitter {
     #[setters(skip)]
     dst: IntoDynSyncSend<Destination>,
-    sm: Option<Lrc<SourceMap>>,
-    fluent_bundle: Option<Lrc<FluentBundle>>,
+    sm: Option<Arc<SourceMap>>,
+    fluent_bundle: Option<Arc<FluentBundle>>,
     #[setters(skip)]
     fallback_bundle: LazyFallbackBundle,
     short_message: bool,
@@ -631,7 +629,7 @@ pub struct HumanEmitter {
 
 #[derive(Debug)]
 pub(crate) struct FileWithAnnotatedLines {
-    pub(crate) file: Lrc<SourceFile>,
+    pub(crate) file: Arc<SourceFile>,
     pub(crate) lines: Vec<Line>,
     multiline_depth: usize,
 }
@@ -715,7 +713,7 @@ impl HumanEmitter {
     fn render_source_line(
         &self,
         buffer: &mut StyledBuffer,
-        file: Lrc<SourceFile>,
+        file: Arc<SourceFile>,
         line: &Line,
         width_offset: usize,
         code_offset: usize,
@@ -1694,7 +1692,7 @@ impl HumanEmitter {
                 // Get the left-side margin to remove it
                 let mut whitespace_margin = usize::MAX;
                 for line_idx in 0..annotated_file.lines.len() {
-                    let file = Lrc::clone(&annotated_file.file);
+                    let file = Arc::clone(&annotated_file.file);
                     let line = &annotated_file.lines[line_idx];
                     if let Some(source_string) =
                         line.line_index.checked_sub(1).and_then(|l| file.get_line(l))
@@ -1767,7 +1765,7 @@ impl HumanEmitter {
 
                 let column_width = if let Some(width) = self.diagnostic_width {
                     width.saturating_sub(code_offset)
-                } else if self.ui_testing {
+                } else if self.ui_testing || cfg!(miri) {
                     DEFAULT_COLUMN_WIDTH
                 } else {
                     termize::dimensions()
@@ -1790,7 +1788,7 @@ impl HumanEmitter {
 
                     let depths = self.render_source_line(
                         &mut buffer,
-                        Lrc::clone(&annotated_file.file),
+                        Arc::clone(&annotated_file.file),
                         &annotated_file.lines[line_idx],
                         width_offset,
                         code_offset,
@@ -2979,7 +2977,7 @@ impl FileWithAnnotatedLines {
     ) -> Vec<FileWithAnnotatedLines> {
         fn add_annotation_to_file(
             file_vec: &mut Vec<FileWithAnnotatedLines>,
-            file: Lrc<SourceFile>,
+            file: Arc<SourceFile>,
             line_index: usize,
             ann: Annotation,
         ) {
@@ -3116,7 +3114,7 @@ impl FileWithAnnotatedLines {
                 //  |        baz
                 add_annotation_to_file(
                     &mut output,
-                    Lrc::clone(&file),
+                    Arc::clone(&file),
                     ann.line_start,
                     ann.as_start(),
                 );
@@ -3143,12 +3141,12 @@ impl FileWithAnnotatedLines {
                     .unwrap_or(ann.line_start);
                 for line in ann.line_start + 1..until {
                     // Every `|` that joins the beginning of the span (`___^`) to the end (`|__^`).
-                    add_annotation_to_file(&mut output, Lrc::clone(&file), line, ann.as_line());
+                    add_annotation_to_file(&mut output, Arc::clone(&file), line, ann.as_line());
                 }
                 let line_end = ann.line_end - 1;
-                let end_is_empty = file.get_line(line_end - 1).map_or(false, |s| !filter(&s));
+                let end_is_empty = file.get_line(line_end - 1).is_some_and(|s| !filter(&s));
                 if middle < line_end && !end_is_empty {
-                    add_annotation_to_file(&mut output, Lrc::clone(&file), line_end, ann.as_line());
+                    add_annotation_to_file(&mut output, Arc::clone(&file), line_end, ann.as_line());
                 }
             } else {
                 end_ann.annotation_type = AnnotationType::Singleline;
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index 97df7f9265a..7d7f364fec2 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -16,12 +16,12 @@ use std::sync::{Arc, Mutex};
 use std::vec;
 
 use derive_setters::Setters;
-use rustc_data_structures::sync::{IntoDynSyncSend, Lrc};
+use rustc_data_structures::sync::IntoDynSyncSend;
 use rustc_error_messages::FluentArgs;
 use rustc_lint_defs::Applicability;
 use rustc_span::Span;
 use rustc_span::hygiene::ExpnData;
-use rustc_span::source_map::SourceMap;
+use rustc_span::source_map::{FilePathMapping, SourceMap};
 use serde::Serialize;
 use termcolor::{ColorSpec, WriteColor};
 
@@ -45,8 +45,8 @@ pub struct JsonEmitter {
     #[setters(skip)]
     dst: IntoDynSyncSend<Box<dyn Write + Send>>,
     #[setters(skip)]
-    sm: Lrc<SourceMap>,
-    fluent_bundle: Option<Lrc<FluentBundle>>,
+    sm: Option<Arc<SourceMap>>,
+    fluent_bundle: Option<Arc<FluentBundle>>,
     #[setters(skip)]
     fallback_bundle: LazyFallbackBundle,
     #[setters(skip)]
@@ -65,7 +65,7 @@ pub struct JsonEmitter {
 impl JsonEmitter {
     pub fn new(
         dst: Box<dyn Write + Send>,
-        sm: Lrc<SourceMap>,
+        sm: Option<Arc<SourceMap>>,
         fallback_bundle: LazyFallbackBundle,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
@@ -171,7 +171,7 @@ impl Emitter for JsonEmitter {
     }
 
     fn source_map(&self) -> Option<&SourceMap> {
-        Some(&self.sm)
+        self.sm.as_deref()
     }
 
     fn should_show_explain(&self) -> bool {
@@ -369,9 +369,9 @@ impl Diagnostic {
             ColorConfig::Always | ColorConfig::Auto => dst = Box::new(termcolor::Ansi::new(dst)),
             ColorConfig::Never => {}
         }
-        HumanEmitter::new(dst, Lrc::clone(&je.fallback_bundle))
+        HumanEmitter::new(dst, Arc::clone(&je.fallback_bundle))
             .short_message(short)
-            .sm(Some(Lrc::clone(&je.sm)))
+            .sm(je.sm.clone())
             .fluent_bundle(je.fluent_bundle.clone())
             .diagnostic_width(je.diagnostic_width)
             .macro_backtrace(je.macro_backtrace)
@@ -458,22 +458,34 @@ impl DiagnosticSpan {
         mut backtrace: impl Iterator<Item = ExpnData>,
         je: &JsonEmitter,
     ) -> DiagnosticSpan {
-        let start = je.sm.lookup_char_pos(span.lo());
+        let empty_source_map;
+        let sm = match &je.sm {
+            Some(s) => s,
+            None => {
+                span = rustc_span::DUMMY_SP;
+                empty_source_map = Arc::new(SourceMap::new(FilePathMapping::empty()));
+                empty_source_map
+                    .new_source_file(std::path::PathBuf::from("empty.rs").into(), String::new());
+                &empty_source_map
+            }
+        };
+        let start = sm.lookup_char_pos(span.lo());
         // If this goes from the start of a line to the end and the replacement
         // is an empty string, increase the length to include the newline so we don't
         // leave an empty line
         if start.col.0 == 0
-            && suggestion.map_or(false, |(s, _)| s.is_empty())
-            && let Ok(after) = je.sm.span_to_next_source(span)
+            && let Some((suggestion, _)) = suggestion
+            && suggestion.is_empty()
+            && let Ok(after) = sm.span_to_next_source(span)
             && after.starts_with('\n')
         {
             span = span.with_hi(span.hi() + rustc_span::BytePos(1));
         }
-        let end = je.sm.lookup_char_pos(span.hi());
+        let end = sm.lookup_char_pos(span.hi());
         let backtrace_step = backtrace.next().map(|bt| {
             let call_site = Self::from_span_full(bt.call_site, false, None, None, backtrace, je);
             let def_site_span = Self::from_span_full(
-                je.sm.guess_head_span(bt.def_site),
+                sm.guess_head_span(bt.def_site),
                 false,
                 None,
                 None,
@@ -488,7 +500,7 @@ impl DiagnosticSpan {
         });
 
         DiagnosticSpan {
-            file_name: je.sm.filename_for_diagnostics(&start.file.name).to_string(),
+            file_name: sm.filename_for_diagnostics(&start.file.name).to_string(),
             byte_start: start.file.original_relative_byte_pos(span.lo()).0,
             byte_end: start.file.original_relative_byte_pos(span.hi()).0,
             line_start: start.line,
@@ -558,19 +570,20 @@ impl DiagnosticSpanLine {
     /// `span` within the line.
     fn from_span(span: Span, je: &JsonEmitter) -> Vec<DiagnosticSpanLine> {
         je.sm
-            .span_to_lines(span)
-            .map(|lines| {
+            .as_ref()
+            .and_then(|sm| {
+                let lines = sm.span_to_lines(span).ok()?;
                 // We can't get any lines if the source is unavailable.
                 if !should_show_source_code(
                     &je.ignored_directories_in_source_blocks,
-                    &je.sm,
+                    &sm,
                     &lines.file,
                 ) {
-                    return vec![];
+                    return None;
                 }
 
                 let sf = &*lines.file;
-                lines
+                let span_lines = lines
                     .lines
                     .iter()
                     .map(|line| {
@@ -581,8 +594,9 @@ impl DiagnosticSpanLine {
                             line.end_col.0 + 1,
                         )
                     })
-                    .collect()
+                    .collect();
+                Some(span_lines)
             })
-            .unwrap_or_else(|_| vec![])
+            .unwrap_or_default()
     }
 }
diff --git a/compiler/rustc_errors/src/json/tests.rs b/compiler/rustc_errors/src/json/tests.rs
index 0de555b83d3..40973e8e5d8 100644
--- a/compiler/rustc_errors/src/json/tests.rs
+++ b/compiler/rustc_errors/src/json/tests.rs
@@ -39,7 +39,7 @@ impl<T: Write> Write for Shared<T> {
 /// Test the span yields correct positions in JSON.
 fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
     rustc_span::create_default_session_globals_then(|| {
-        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sm = Arc::new(SourceMap::new(FilePathMapping::empty()));
         sm.new_source_file(Path::new("test.rs").to_owned().into(), code.to_owned());
         let fallback_bundle =
             crate::fallback_fluent_bundle(vec![crate::DEFAULT_LOCALE_RESOURCE], false);
@@ -47,7 +47,7 @@ fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
         let output = Arc::new(Mutex::new(Vec::new()));
         let je = JsonEmitter::new(
             Box::new(Shared { data: output.clone() }),
-            sm,
+            Some(sm),
             fallback_bundle,
             true, // pretty
             HumanReadableErrorType::Short,
@@ -69,96 +69,128 @@ fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
 
 #[test]
 fn empty() {
-    test_positions(" ", (0, 1), SpanTestData {
-        byte_start: 0,
-        byte_end: 1,
-        line_start: 1,
-        column_start: 1,
-        line_end: 1,
-        column_end: 2,
-    })
+    test_positions(
+        " ",
+        (0, 1),
+        SpanTestData {
+            byte_start: 0,
+            byte_end: 1,
+            line_start: 1,
+            column_start: 1,
+            line_end: 1,
+            column_end: 2,
+        },
+    )
 }
 
 #[test]
 fn bom() {
-    test_positions("\u{feff} ", (0, 1), SpanTestData {
-        byte_start: 3,
-        byte_end: 4,
-        line_start: 1,
-        column_start: 1,
-        line_end: 1,
-        column_end: 2,
-    })
+    test_positions(
+        "\u{feff} ",
+        (0, 1),
+        SpanTestData {
+            byte_start: 3,
+            byte_end: 4,
+            line_start: 1,
+            column_start: 1,
+            line_end: 1,
+            column_end: 2,
+        },
+    )
 }
 
 #[test]
 fn lf_newlines() {
-    test_positions("\nmod foo;\nmod bar;\n", (5, 12), SpanTestData {
-        byte_start: 5,
-        byte_end: 12,
-        line_start: 2,
-        column_start: 5,
-        line_end: 3,
-        column_end: 3,
-    })
+    test_positions(
+        "\nmod foo;\nmod bar;\n",
+        (5, 12),
+        SpanTestData {
+            byte_start: 5,
+            byte_end: 12,
+            line_start: 2,
+            column_start: 5,
+            line_end: 3,
+            column_end: 3,
+        },
+    )
 }
 
 #[test]
 fn crlf_newlines() {
-    test_positions("\r\nmod foo;\r\nmod bar;\r\n", (5, 12), SpanTestData {
-        byte_start: 6,
-        byte_end: 14,
-        line_start: 2,
-        column_start: 5,
-        line_end: 3,
-        column_end: 3,
-    })
+    test_positions(
+        "\r\nmod foo;\r\nmod bar;\r\n",
+        (5, 12),
+        SpanTestData {
+            byte_start: 6,
+            byte_end: 14,
+            line_start: 2,
+            column_start: 5,
+            line_end: 3,
+            column_end: 3,
+        },
+    )
 }
 
 #[test]
 fn crlf_newlines_with_bom() {
-    test_positions("\u{feff}\r\nmod foo;\r\nmod bar;\r\n", (5, 12), SpanTestData {
-        byte_start: 9,
-        byte_end: 17,
-        line_start: 2,
-        column_start: 5,
-        line_end: 3,
-        column_end: 3,
-    })
+    test_positions(
+        "\u{feff}\r\nmod foo;\r\nmod bar;\r\n",
+        (5, 12),
+        SpanTestData {
+            byte_start: 9,
+            byte_end: 17,
+            line_start: 2,
+            column_start: 5,
+            line_end: 3,
+            column_end: 3,
+        },
+    )
 }
 
 #[test]
 fn span_before_crlf() {
-    test_positions("foo\r\nbar", (2, 3), SpanTestData {
-        byte_start: 2,
-        byte_end: 3,
-        line_start: 1,
-        column_start: 3,
-        line_end: 1,
-        column_end: 4,
-    })
+    test_positions(
+        "foo\r\nbar",
+        (2, 3),
+        SpanTestData {
+            byte_start: 2,
+            byte_end: 3,
+            line_start: 1,
+            column_start: 3,
+            line_end: 1,
+            column_end: 4,
+        },
+    )
 }
 
 #[test]
 fn span_on_crlf() {
-    test_positions("foo\r\nbar", (3, 4), SpanTestData {
-        byte_start: 3,
-        byte_end: 5,
-        line_start: 1,
-        column_start: 4,
-        line_end: 2,
-        column_end: 1,
-    })
+    test_positions(
+        "foo\r\nbar",
+        (3, 4),
+        SpanTestData {
+            byte_start: 3,
+            byte_end: 5,
+            line_start: 1,
+            column_start: 4,
+            line_end: 2,
+            column_end: 1,
+        },
+    )
 }
 
 #[test]
 fn span_after_crlf() {
-    test_positions("foo\r\nbar", (4, 5), SpanTestData {
-        byte_start: 5,
-        byte_end: 6,
-        line_start: 2,
-        column_start: 1,
-        line_end: 2,
-        column_end: 2,
-    })
+    test_positions(
+        "foo\r\nbar",
+        (4, 5),
+        SpanTestData {
+            byte_start: 5,
+            byte_end: 6,
+            line_start: 2,
+            column_start: 1,
+            line_end: 2,
+            column_end: 2,
+        },
+    )
 }
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index cc5eb9c335e..9af17db9a6e 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -35,6 +35,7 @@ use std::backtrace::{Backtrace, BacktraceStatus};
 use std::borrow::Cow;
 use std::cell::Cell;
 use std::error::Report;
+use std::ffi::OsStr;
 use std::hash::Hash;
 use std::io::Write;
 use std::num::NonZero;
@@ -58,13 +59,13 @@ use emitter::{DynEmitter, Emitter, is_case_difference, is_different};
 use rustc_data_structures::AtomicRef;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::stable_hasher::{Hash128, StableHasher};
-use rustc_data_structures::sync::Lock;
+use rustc_data_structures::sync::{DynSend, Lock};
 pub use rustc_error_messages::{
     DiagMessage, FluentBundle, LanguageIdentifier, LazyFallbackBundle, MultiSpan, SpanLabel,
     SubdiagMessage, fallback_fluent_bundle, fluent_bundle,
 };
 use rustc_lint_defs::LintExpectationId;
-pub use rustc_lint_defs::{Applicability, pluralize};
+pub use rustc_lint_defs::{Applicability, listify, pluralize};
 use rustc_macros::{Decodable, Encodable};
 pub use rustc_span::ErrorGuaranteed;
 pub use rustc_span::fatal_error::{FatalError, FatalErrorMarker};
@@ -675,57 +676,44 @@ impl DiagCtxt {
         Self { inner: Lock::new(DiagCtxtInner::new(emitter)) }
     }
 
-    pub fn make_silent(
-        &self,
-        fallback_bundle: LazyFallbackBundle,
-        fatal_note: Option<String>,
-        emit_fatal_diagnostic: bool,
-    ) {
-        self.wrap_emitter(|old_dcx| {
-            Box::new(emitter::SilentEmitter {
-                fallback_bundle,
-                fatal_dcx: DiagCtxt { inner: Lock::new(old_dcx) },
-                fatal_note,
-                emit_fatal_diagnostic,
-            })
-        });
-    }
-
-    fn wrap_emitter<F>(&self, f: F)
-    where
-        F: FnOnce(DiagCtxtInner) -> Box<DynEmitter>,
-    {
-        // A empty type that implements `Emitter` so that a `DiagCtxtInner` can be constructed
-        // to temporarily swap in place of the real one, which will be used in constructing
-        // its replacement.
+    pub fn make_silent(&self, fatal_note: Option<String>, emit_fatal_diagnostic: bool) {
+        // An empty type that implements `Emitter` to temporarily swap in place of the real one,
+        // which will be used in constructing its replacement.
         struct FalseEmitter;
 
         impl Emitter for FalseEmitter {
             fn emit_diagnostic(&mut self, _: DiagInner, _: &Registry) {
-                unimplemented!("false emitter must only used during `wrap_emitter`")
+                unimplemented!("false emitter must only used during `make_silent`")
             }
 
             fn source_map(&self) -> Option<&SourceMap> {
-                unimplemented!("false emitter must only used during `wrap_emitter`")
+                unimplemented!("false emitter must only used during `make_silent`")
             }
         }
 
         impl translation::Translate for FalseEmitter {
             fn fluent_bundle(&self) -> Option<&FluentBundle> {
-                unimplemented!("false emitter must only used during `wrap_emitter`")
+                unimplemented!("false emitter must only used during `make_silent`")
             }
 
             fn fallback_fluent_bundle(&self) -> &FluentBundle {
-                unimplemented!("false emitter must only used during `wrap_emitter`")
+                unimplemented!("false emitter must only used during `make_silent`")
             }
         }
 
         let mut inner = self.inner.borrow_mut();
-        let mut prev_dcx = DiagCtxtInner::new(Box::new(FalseEmitter));
-        std::mem::swap(&mut *inner, &mut prev_dcx);
-        let new_emitter = f(prev_dcx);
-        let mut new_dcx = DiagCtxtInner::new(new_emitter);
-        std::mem::swap(&mut *inner, &mut new_dcx);
+        let mut prev_emitter = Box::new(FalseEmitter) as Box<dyn Emitter + DynSend>;
+        std::mem::swap(&mut inner.emitter, &mut prev_emitter);
+        let new_emitter = Box::new(emitter::SilentEmitter {
+            fatal_emitter: prev_emitter,
+            fatal_note,
+            emit_fatal_diagnostic,
+        });
+        inner.emitter = new_emitter;
+    }
+
+    pub fn set_emitter(&self, emitter: Box<dyn Emitter + DynSend>) {
+        self.inner.borrow_mut().emitter = emitter;
     }
 
     /// Translate `message` eagerly with `args` to `SubdiagMessage::Eager`.
@@ -1060,8 +1048,8 @@ impl<'a> DiagCtxtHandle<'a> {
     /// bad results, such as spurious/uninteresting additional errors -- when
     /// returning an error `Result` is difficult.
     pub fn abort_if_errors(&self) {
-        if self.has_errors().is_some() {
-            FatalError.raise();
+        if let Some(guar) = self.has_errors() {
+            guar.raise_fatal();
         }
     }
 
@@ -1717,7 +1705,7 @@ impl DiagCtxtInner {
         let bugs: Vec<_> =
             std::mem::take(&mut self.delayed_bugs).into_iter().map(|(b, _)| b).collect();
 
-        let backtrace = std::env::var_os("RUST_BACKTRACE").map_or(true, |x| &x != "0");
+        let backtrace = std::env::var_os("RUST_BACKTRACE").as_deref() != Some(OsStr::new("0"));
         let decorate = backtrace || self.ice_file.is_none();
         let mut out = self
             .ice_file
@@ -1998,18 +1986,6 @@ pub fn a_or_an(s: &str) -> &'static str {
     }
 }
 
-/// Grammatical tool for displaying messages to end users in a nice form.
-///
-/// Take a list ["a", "b", "c"] and output a display friendly version "a, b and c"
-pub fn display_list_with_comma_and<T: std::fmt::Display>(v: &[T]) -> String {
-    match v {
-        [] => "".to_string(),
-        [a] => a.to_string(),
-        [a, b] => format!("{a} and {b}"),
-        [a, v @ ..] => format!("{a}, {}", display_list_with_comma_and(v)),
-    }
-}
-
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum TerminalUrl {
     No,