Auto merge of #74862 - mark-i-m:mv-compiler, r=petrochenkov

Move almost all compiler crates to compiler/

This PR implements https://github.com/rust-lang/compiler-team/issues/336 and moves all `rustc_*` crates from `src` to the new `compiler` directory.

`librustc_foo` directories are renamed to `rustc_foo`.
`src` directories are introduced inside `rustc_*` directories to mirror the scheme already use for `library` crates.

1 files changed, 1021 insertions, 0 deletions

diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
new file mode 100644
index 00000000000..d4f0a9d83ef
--- /dev/null
+++ b/compiler/rustc_errors/src/lib.rs
@@ -0,0 +1,1021 @@
+//! Diagnostics creation and emission for `rustc`.
+//!
+//! This module contains the code for creating and emitting diagnostics.
+
+#![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
+#![feature(crate_visibility_modifier)]
+#![feature(nll)]
+
+#[macro_use]
+extern crate rustc_macros;
+
+pub use emitter::ColorConfig;
+
+use tracing::debug;
+use Level::*;
+
+use emitter::{is_case_difference, Emitter, EmitterWriter};
+use registry::Registry;
+use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
+use rustc_data_structures::stable_hasher::StableHasher;
+use rustc_data_structures::sync::{self, Lock, Lrc};
+use rustc_data_structures::AtomicRef;
+use rustc_span::source_map::SourceMap;
+use rustc_span::{Loc, MultiSpan, Span};
+
+use std::borrow::Cow;
+use std::panic;
+use std::path::Path;
+use std::{error, fmt};
+
+use termcolor::{Color, ColorSpec};
+
+pub mod annotate_snippet_emitter_writer;
+mod diagnostic;
+mod diagnostic_builder;
+pub mod emitter;
+pub mod json;
+mod lock;
+pub mod registry;
+mod snippet;
+mod styled_buffer;
+pub use snippet::Style;
+
+pub type PResult<'a, T> = Result<T, DiagnosticBuilder<'a>>;
+
+// `PResult` is used a lot. Make sure it doesn't unintentionally get bigger.
+// (See also the comment on `DiagnosticBuilderInner`.)
+#[cfg(target_arch = "x86_64")]
+rustc_data_structures::static_assert_size!(PResult<'_, bool>, 16);
+
+/// Indicates the confidence in the correctness of a suggestion.
+///
+/// All suggestions are marked with an `Applicability`. Tools use the applicability of a suggestion
+/// to determine whether it should be automatically applied or if the user should be consulted
+/// before applying the suggestion.
+#[derive(Copy, Clone, Debug, PartialEq, Hash, Encodable, Decodable)]
+pub enum Applicability {
+    /// The suggestion is definitely what the user intended. This suggestion should be
+    /// automatically applied.
+    MachineApplicable,
+
+    /// The suggestion may be what the user intended, but it is uncertain. The suggestion should
+    /// result in valid Rust code if it is applied.
+    MaybeIncorrect,
+
+    /// The suggestion contains placeholders like `(...)` or `{ /* fields */ }`. The suggestion
+    /// cannot be applied automatically because it will not result in valid Rust code. The user
+    /// will need to fill in the placeholders.
+    HasPlaceholders,
+
+    /// The applicability of the suggestion is unknown.
+    Unspecified,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, Encodable, Decodable)]
+pub enum SuggestionStyle {
+    /// Hide the suggested code when displaying this suggestion inline.
+    HideCodeInline,
+    /// Always hide the suggested code but display the message.
+    HideCodeAlways,
+    /// Do not display this suggestion in the cli output, it is only meant for tools.
+    CompletelyHidden,
+    /// Always show the suggested code.
+    /// This will *not* show the code if the suggestion is inline *and* the suggested code is
+    /// empty.
+    ShowCode,
+    /// Always show the suggested code independently.
+    ShowAlways,
+}
+
+impl SuggestionStyle {
+    fn hide_inline(&self) -> bool {
+        match *self {
+            SuggestionStyle::ShowCode => false,
+            _ => true,
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Hash, Encodable, Decodable)]
+pub struct CodeSuggestion {
+    /// Each substitute can have multiple variants due to multiple
+    /// applicable suggestions
+    ///
+    /// `foo.bar` might be replaced with `a.b` or `x.y` by replacing
+    /// `foo` and `bar` on their own:
+    ///
+    /// ```
+    /// vec![
+    ///     Substitution { parts: vec![(0..3, "a"), (4..7, "b")] },
+    ///     Substitution { parts: vec![(0..3, "x"), (4..7, "y")] },
+    /// ]
+    /// ```
+    ///
+    /// or by replacing the entire span:
+    ///
+    /// ```
+    /// vec![
+    ///     Substitution { parts: vec![(0..7, "a.b")] },
+    ///     Substitution { parts: vec![(0..7, "x.y")] },
+    /// ]
+    /// ```
+    pub substitutions: Vec<Substitution>,
+    pub msg: String,
+    /// Visual representation of this suggestion.
+    pub style: SuggestionStyle,
+    /// Whether or not the suggestion is approximate
+    ///
+    /// Sometimes we may show suggestions with placeholders,
+    /// which are useful for users but not useful for
+    /// tools like rustfix
+    pub applicability: Applicability,
+}
+
+#[derive(Clone, Debug, PartialEq, Hash, Encodable, Decodable)]
+/// See the docs on `CodeSuggestion::substitutions`
+pub struct Substitution {
+    pub parts: Vec<SubstitutionPart>,
+}
+
+#[derive(Clone, Debug, PartialEq, Hash, Encodable, Decodable)]
+pub struct SubstitutionPart {
+    pub span: Span,
+    pub snippet: String,
+}
+
+impl CodeSuggestion {
+    /// Returns the assembled code suggestions, whether they should be shown with an underline
+    /// and whether the substitution only differs in capitalization.
+    pub fn splice_lines(&self, sm: &SourceMap) -> Vec<(String, Vec<SubstitutionPart>, bool)> {
+        use rustc_span::{CharPos, Pos};
+
+        fn push_trailing(
+            buf: &mut String,
+            line_opt: Option<&Cow<'_, str>>,
+            lo: &Loc,
+            hi_opt: Option<&Loc>,
+        ) {
+            let (lo, hi_opt) = (lo.col.to_usize(), hi_opt.map(|hi| hi.col.to_usize()));
+            if let Some(line) = line_opt {
+                if let Some(lo) = line.char_indices().map(|(i, _)| i).nth(lo) {
+                    let hi_opt = hi_opt.and_then(|hi| line.char_indices().map(|(i, _)| i).nth(hi));
+                    match hi_opt {
+                        Some(hi) if hi > lo => buf.push_str(&line[lo..hi]),
+                        Some(_) => (),
+                        None => buf.push_str(&line[lo..]),
+                    }
+                }
+                if hi_opt.is_none() {
+                    buf.push('\n');
+                }
+            }
+        }
+
+        assert!(!self.substitutions.is_empty());
+
+        self.substitutions
+            .iter()
+            .filter(|subst| {
+                // Suggestions coming from macros can have malformed spans. This is a heavy
+                // handed approach to avoid ICEs by ignoring the suggestion outright.
+                let invalid = subst.parts.iter().any(|item| sm.is_valid_span(item.span).is_err());
+                if invalid {
+                    debug!("splice_lines: suggestion contains an invalid span: {:?}", subst);
+                }
+                !invalid
+            })
+            .cloned()
+            .filter_map(|mut substitution| {
+                // Assumption: all spans are in the same file, and all spans
+                // are disjoint. Sort in ascending order.
+                substitution.parts.sort_by_key(|part| part.span.lo());
+
+                // Find the bounding span.
+                let lo = substitution.parts.iter().map(|part| part.span.lo()).min()?;
+                let hi = substitution.parts.iter().map(|part| part.span.hi()).max()?;
+                let bounding_span = Span::with_root_ctxt(lo, hi);
+                // The different spans might belong to different contexts, if so ignore suggestion.
+                let lines = sm.span_to_lines(bounding_span).ok()?;
+                assert!(!lines.lines.is_empty() || bounding_span.is_dummy());
+
+                // We can't splice anything if the source is unavailable.
+                if !sm.ensure_source_file_source_present(lines.file.clone()) {
+                    return None;
+                }
+
+                // To build up the result, we do this for each span:
+                // - push the line segment trailing the previous span
+                //   (at the beginning a "phantom" span pointing at the start of the line)
+                // - push lines between the previous and current span (if any)
+                // - if the previous and current span are not on the same line
+                //   push the line segment leading up to the current span
+                // - splice in the span substitution
+                //
+                // Finally push the trailing line segment of the last span
+                let sf = &lines.file;
+                let mut prev_hi = sm.lookup_char_pos(bounding_span.lo());
+                prev_hi.col = CharPos::from_usize(0);
+                let mut prev_line =
+                    lines.lines.get(0).and_then(|line0| sf.get_line(line0.line_index));
+                let mut buf = String::new();
+
+                for part in &substitution.parts {
+                    let cur_lo = sm.lookup_char_pos(part.span.lo());
+                    if prev_hi.line == cur_lo.line {
+                        push_trailing(&mut buf, prev_line.as_ref(), &prev_hi, Some(&cur_lo));
+                    } else {
+                        push_trailing(&mut buf, prev_line.as_ref(), &prev_hi, None);
+                        // push lines between the previous and current span (if any)
+                        for idx in prev_hi.line..(cur_lo.line - 1) {
+                            if let Some(line) = sf.get_line(idx) {
+                                buf.push_str(line.as_ref());
+                                buf.push('\n');
+                            }
+                        }
+                        if let Some(cur_line) = sf.get_line(cur_lo.line - 1) {
+                            let end = match cur_line.char_indices().nth(cur_lo.col.to_usize()) {
+                                Some((i, _)) => i,
+                                None => cur_line.len(),
+                            };
+                            buf.push_str(&cur_line[..end]);
+                        }
+                    }
+                    buf.push_str(&part.snippet);
+                    prev_hi = sm.lookup_char_pos(part.span.hi());
+                    prev_line = sf.get_line(prev_hi.line - 1);
+                }
+                let only_capitalization = is_case_difference(sm, &buf, bounding_span);
+                // if the replacement already ends with a newline, don't print the next line
+                if !buf.ends_with('\n') {
+                    push_trailing(&mut buf, prev_line.as_ref(), &prev_hi, None);
+                }
+                // remove trailing newlines
+                while buf.ends_with('\n') {
+                    buf.pop();
+                }
+                Some((buf, substitution.parts, only_capitalization))
+            })
+            .collect()
+    }
+}
+
+pub use rustc_span::fatal_error::{FatalError, FatalErrorMarker};
+
+/// Signifies that the compiler died with an explicit call to `.bug`
+/// or `.span_bug` rather than a failed assertion, etc.
+#[derive(Copy, Clone, Debug)]
+pub struct ExplicitBug;
+
+impl fmt::Display for ExplicitBug {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "parser internal bug")
+    }
+}
+
+impl error::Error for ExplicitBug {}
+
+pub use diagnostic::{Diagnostic, DiagnosticId, DiagnosticStyledString, SubDiagnostic};
+pub use diagnostic_builder::DiagnosticBuilder;
+
+/// A handler deals with errors and other compiler output.
+/// Certain errors (fatal, bug, unimpl) may cause immediate exit,
+/// others log errors for later reporting.
+pub struct Handler {
+    flags: HandlerFlags,
+    inner: Lock<HandlerInner>,
+}
+
+/// This inner struct exists to keep it all behind a single lock;
+/// this is done to prevent possible deadlocks in a multi-threaded compiler,
+/// as well as inconsistent state observation.
+struct HandlerInner {
+    flags: HandlerFlags,
+    /// The number of errors that have been emitted, including duplicates.
+    ///
+    /// This is not necessarily the count that's reported to the user once
+    /// compilation ends.
+    err_count: usize,
+    deduplicated_err_count: usize,
+    emitter: Box<dyn Emitter + sync::Send>,
+    delayed_span_bugs: Vec<Diagnostic>,
+
+    /// This set contains the `DiagnosticId` of all emitted diagnostics to avoid
+    /// emitting the same diagnostic with extended help (`--teach`) twice, which
+    /// would be uneccessary repetition.
+    taught_diagnostics: FxHashSet<DiagnosticId>,
+
+    /// Used to suggest rustc --explain <error code>
+    emitted_diagnostic_codes: FxHashSet<DiagnosticId>,
+
+    /// This set contains a hash of every diagnostic that has been emitted by
+    /// this handler. These hashes is used to avoid emitting the same error
+    /// twice.
+    emitted_diagnostics: FxHashSet<u128>,
+
+    /// Stashed diagnostics emitted in one stage of the compiler that may be
+    /// stolen by other stages (e.g. to improve them and add more information).
+    /// The stashed diagnostics count towards the total error count.
+    /// When `.abort_if_errors()` is called, these are also emitted.
+    stashed_diagnostics: FxIndexMap<(Span, StashKey), Diagnostic>,
+
+    /// The warning count, used for a recap upon finishing
+    deduplicated_warn_count: usize,
+}
+
+/// A key denoting where from a diagnostic was stashed.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum StashKey {
+    ItemNoType,
+}
+
+fn default_track_diagnostic(_: &Diagnostic) {}
+
+pub static TRACK_DIAGNOSTICS: AtomicRef<fn(&Diagnostic)> =
+    AtomicRef::new(&(default_track_diagnostic as fn(&_)));
+
+#[derive(Copy, Clone, Default)]
+pub struct HandlerFlags {
+    /// If false, warning-level lints are suppressed.
+    /// (rustc: see `--allow warnings` and `--cap-lints`)
+    pub can_emit_warnings: bool,
+    /// If true, error-level diagnostics are upgraded to bug-level.
+    /// (rustc: see `-Z treat-err-as-bug`)
+    pub treat_err_as_bug: Option<usize>,
+    /// If true, immediately emit diagnostics that would otherwise be buffered.
+    /// (rustc: see `-Z dont-buffer-diagnostics` and `-Z treat-err-as-bug`)
+    pub dont_buffer_diagnostics: bool,
+    /// If true, immediately print bugs registered with `delay_span_bug`.
+    /// (rustc: see `-Z report-delayed-bugs`)
+    pub report_delayed_bugs: bool,
+    /// Show macro backtraces.
+    /// (rustc: see `-Z macro-backtrace`)
+    pub macro_backtrace: bool,
+    /// If true, identical diagnostics are reported only once.
+    pub deduplicate_diagnostics: bool,
+}
+
+impl Drop for HandlerInner {
+    fn drop(&mut self) {
+        self.emit_stashed_diagnostics();
+
+        if !self.has_errors() {
+            let bugs = std::mem::replace(&mut self.delayed_span_bugs, Vec::new());
+            let has_bugs = !bugs.is_empty();
+            for bug in bugs {
+                self.emit_diagnostic(&bug);
+            }
+            if has_bugs {
+                panic!("no errors encountered even though `delay_span_bug` issued");
+            }
+        }
+    }
+}
+
+impl Handler {
+    pub fn with_tty_emitter(
+        color_config: ColorConfig,
+        can_emit_warnings: bool,
+        treat_err_as_bug: Option<usize>,
+        sm: Option<Lrc<SourceMap>>,
+    ) -> Self {
+        Self::with_tty_emitter_and_flags(
+            color_config,
+            sm,
+            HandlerFlags { can_emit_warnings, treat_err_as_bug, ..Default::default() },
+        )
+    }
+
+    pub fn with_tty_emitter_and_flags(
+        color_config: ColorConfig,
+        sm: Option<Lrc<SourceMap>>,
+        flags: HandlerFlags,
+    ) -> Self {
+        let emitter = Box::new(EmitterWriter::stderr(
+            color_config,
+            sm,
+            false,
+            false,
+            None,
+            flags.macro_backtrace,
+        ));
+        Self::with_emitter_and_flags(emitter, flags)
+    }
+
+    pub fn with_emitter(
+        can_emit_warnings: bool,
+        treat_err_as_bug: Option<usize>,
+        emitter: Box<dyn Emitter + sync::Send>,
+    ) -> Self {
+        Handler::with_emitter_and_flags(
+            emitter,
+            HandlerFlags { can_emit_warnings, treat_err_as_bug, ..Default::default() },
+        )
+    }
+
+    pub fn with_emitter_and_flags(
+        emitter: Box<dyn Emitter + sync::Send>,
+        flags: HandlerFlags,
+    ) -> Self {
+        Self {
+            flags,
+            inner: Lock::new(HandlerInner {
+                flags,
+                err_count: 0,
+                deduplicated_err_count: 0,
+                deduplicated_warn_count: 0,
+                emitter,
+                delayed_span_bugs: Vec::new(),
+                taught_diagnostics: Default::default(),
+                emitted_diagnostic_codes: Default::default(),
+                emitted_diagnostics: Default::default(),
+                stashed_diagnostics: Default::default(),
+            }),
+        }
+    }
+
+    // This is here to not allow mutation of flags;
+    // as of this writing it's only used in tests in librustc_middle.
+    pub fn can_emit_warnings(&self) -> bool {
+        self.flags.can_emit_warnings
+    }
+
+    /// Resets the diagnostic error count as well as the cached emitted diagnostics.
+    ///
+    /// NOTE: *do not* call this function from rustc. It is only meant to be called from external
+    /// tools that want to reuse a `Parser` cleaning the previously emitted diagnostics as well as
+    /// the overall count of emitted error diagnostics.
+    pub fn reset_err_count(&self) {
+        let mut inner = self.inner.borrow_mut();
+        inner.err_count = 0;
+        inner.deduplicated_err_count = 0;
+        inner.deduplicated_warn_count = 0;
+
+        // actually free the underlying memory (which `clear` would not do)
+        inner.delayed_span_bugs = Default::default();
+        inner.taught_diagnostics = Default::default();
+        inner.emitted_diagnostic_codes = Default::default();
+        inner.emitted_diagnostics = Default::default();
+        inner.stashed_diagnostics = Default::default();
+    }
+
+    /// Stash a given diagnostic with the given `Span` and `StashKey` as the key for later stealing.
+    pub fn stash_diagnostic(&self, span: Span, key: StashKey, diag: Diagnostic) {
+        let mut inner = self.inner.borrow_mut();
+        // FIXME(Centril, #69537): Consider reintroducing panic on overwriting a stashed diagnostic
+        // if/when we have a more robust macro-friendly replacement for `(span, key)` as a key.
+        // See the PR for a discussion.
+        inner.stashed_diagnostics.insert((span, key), diag);
+    }
+
+    /// Steal a previously stashed diagnostic with the given `Span` and `StashKey` as the key.
+    pub fn steal_diagnostic(&self, span: Span, key: StashKey) -> Option<DiagnosticBuilder<'_>> {
+        self.inner
+            .borrow_mut()
+            .stashed_diagnostics
+            .remove(&(span, key))
+            .map(|diag| DiagnosticBuilder::new_diagnostic(self, diag))
+    }
+
+    /// Emit all stashed diagnostics.
+    pub fn emit_stashed_diagnostics(&self) {
+        self.inner.borrow_mut().emit_stashed_diagnostics();
+    }
+
+    /// Construct a dummy builder with `Level::Cancelled`.
+    ///
+    /// Using this will neither report anything to the user (e.g. a warning),
+    /// nor will compilation cancel as a result.
+    pub fn struct_dummy(&self) -> DiagnosticBuilder<'_> {
+        DiagnosticBuilder::new(self, Level::Cancelled, "")
+    }
+
+    /// Construct a builder at the `Warning` level at the given `span` and with the `msg`.
+    pub fn struct_span_warn(&self, span: impl Into<MultiSpan>, msg: &str) -> DiagnosticBuilder<'_> {
+        let mut result = self.struct_warn(msg);
+        result.set_span(span);
+        result
+    }
+
+    /// Construct a builder at the `Warning` level at the given `span` and with the `msg`.
+    /// Also include a code.
+    pub fn struct_span_warn_with_code(
+        &self,
+        span: impl Into<MultiSpan>,
+        msg: &str,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_> {
+        let mut result = self.struct_span_warn(span, msg);
+        result.code(code);
+        result
+    }
+
+    /// Construct a builder at the `Warning` level with the `msg`.
+    pub fn struct_warn(&self, msg: &str) -> DiagnosticBuilder<'_> {
+        let mut result = DiagnosticBuilder::new(self, Level::Warning, msg);
+        if !self.flags.can_emit_warnings {
+            result.cancel();
+        }
+        result
+    }
+
+    /// Construct a builder at the `Error` level at the given `span` and with the `msg`.
+    pub fn struct_span_err(&self, span: impl Into<MultiSpan>, msg: &str) -> DiagnosticBuilder<'_> {
+        let mut result = self.struct_err(msg);
+        result.set_span(span);
+        result
+    }
+
+    /// Construct a builder at the `Error` level at the given `span`, with the `msg`, and `code`.
+    pub fn struct_span_err_with_code(
+        &self,
+        span: impl Into<MultiSpan>,
+        msg: &str,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_> {
+        let mut result = self.struct_span_err(span, msg);
+        result.code(code);
+        result
+    }
+
+    /// Construct a builder at the `Error` level with the `msg`.
+    // FIXME: This method should be removed (every error should have an associated error code).
+    pub fn struct_err(&self, msg: &str) -> DiagnosticBuilder<'_> {
+        DiagnosticBuilder::new(self, Level::Error, msg)
+    }
+
+    /// Construct a builder at the `Error` level with the `msg` and the `code`.
+    pub fn struct_err_with_code(&self, msg: &str, code: DiagnosticId) -> DiagnosticBuilder<'_> {
+        let mut result = self.struct_err(msg);
+        result.code(code);
+        result
+    }
+
+    /// Construct a builder at the `Fatal` level at the given `span` and with the `msg`.
+    pub fn struct_span_fatal(
+        &self,
+        span: impl Into<MultiSpan>,
+        msg: &str,
+    ) -> DiagnosticBuilder<'_> {
+        let mut result = self.struct_fatal(msg);
+        result.set_span(span);
+        result
+    }
+
+    /// Construct a builder at the `Fatal` level at the given `span`, with the `msg`, and `code`.
+    pub fn struct_span_fatal_with_code(
+        &self,
+        span: impl Into<MultiSpan>,
+        msg: &str,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_> {
+        let mut result = self.struct_span_fatal(span, msg);
+        result.code(code);
+        result
+    }
+
+    /// Construct a builder at the `Error` level with the `msg`.
+    pub fn struct_fatal(&self, msg: &str) -> DiagnosticBuilder<'_> {
+        DiagnosticBuilder::new(self, Level::Fatal, msg)
+    }
+
+    /// Construct a builder at the `Help` level with the `msg`.
+    pub fn struct_help(&self, msg: &str) -> DiagnosticBuilder<'_> {
+        DiagnosticBuilder::new(self, Level::Help, msg)
+    }
+
+    /// Construct a builder at the `Note` level with the `msg`.
+    pub fn struct_note_without_error(&self, msg: &str) -> DiagnosticBuilder<'_> {
+        DiagnosticBuilder::new(self, Level::Note, msg)
+    }
+
+    pub fn span_fatal(&self, span: impl Into<MultiSpan>, msg: &str) -> FatalError {
+        self.emit_diag_at_span(Diagnostic::new(Fatal, msg), span);
+        FatalError
+    }
+
+    pub fn span_fatal_with_code(
+        &self,
+        span: impl Into<MultiSpan>,
+        msg: &str,
+        code: DiagnosticId,
+    ) -> FatalError {
+        self.emit_diag_at_span(Diagnostic::new_with_code(Fatal, Some(code), msg), span);
+        FatalError
+    }
+
+    pub fn span_err(&self, span: impl Into<MultiSpan>, msg: &str) {
+        self.emit_diag_at_span(Diagnostic::new(Error, msg), span);
+    }
+
+    pub fn span_err_with_code(&self, span: impl Into<MultiSpan>, msg: &str, code: DiagnosticId) {
+        self.emit_diag_at_span(Diagnostic::new_with_code(Error, Some(code), msg), span);
+    }
+
+    pub fn span_warn(&self, span: impl Into<MultiSpan>, msg: &str) {
+        self.emit_diag_at_span(Diagnostic::new(Warning, msg), span);
+    }
+
+    pub fn span_warn_with_code(&self, span: impl Into<MultiSpan>, msg: &str, code: DiagnosticId) {
+        self.emit_diag_at_span(Diagnostic::new_with_code(Warning, Some(code), msg), span);
+    }
+
+    pub fn span_bug(&self, span: impl Into<MultiSpan>, msg: &str) -> ! {
+        self.inner.borrow_mut().span_bug(span, msg)
+    }
+
+    #[track_caller]
+    pub fn delay_span_bug(&self, span: impl Into<MultiSpan>, msg: &str) {
+        self.inner.borrow_mut().delay_span_bug(span, msg)
+    }
+
+    pub fn span_bug_no_panic(&self, span: impl Into<MultiSpan>, msg: &str) {
+        self.emit_diag_at_span(Diagnostic::new(Bug, msg), span);
+    }
+
+    pub fn span_note_without_error(&self, span: impl Into<MultiSpan>, msg: &str) {
+        self.emit_diag_at_span(Diagnostic::new(Note, msg), span);
+    }
+
+    pub fn span_note_diag(&self, span: Span, msg: &str) -> DiagnosticBuilder<'_> {
+        let mut db = DiagnosticBuilder::new(self, Note, msg);
+        db.set_span(span);
+        db
+    }
+
+    pub fn failure(&self, msg: &str) {
+        self.inner.borrow_mut().failure(msg);
+    }
+
+    pub fn fatal(&self, msg: &str) -> FatalError {
+        self.inner.borrow_mut().fatal(msg)
+    }
+
+    pub fn err(&self, msg: &str) {
+        self.inner.borrow_mut().err(msg);
+    }
+
+    pub fn warn(&self, msg: &str) {
+        let mut db = DiagnosticBuilder::new(self, Warning, msg);
+        db.emit();
+    }
+
+    pub fn note_without_error(&self, msg: &str) {
+        DiagnosticBuilder::new(self, Note, msg).emit();
+    }
+
+    pub fn bug(&self, msg: &str) -> ! {
+        self.inner.borrow_mut().bug(msg)
+    }
+
+    pub fn err_count(&self) -> usize {
+        self.inner.borrow().err_count()
+    }
+
+    pub fn has_errors(&self) -> bool {
+        self.inner.borrow().has_errors()
+    }
+    pub fn has_errors_or_delayed_span_bugs(&self) -> bool {
+        self.inner.borrow().has_errors_or_delayed_span_bugs()
+    }
+
+    pub fn print_error_count(&self, registry: &Registry) {
+        self.inner.borrow_mut().print_error_count(registry)
+    }
+
+    pub fn abort_if_errors(&self) {
+        self.inner.borrow_mut().abort_if_errors()
+    }
+
+    /// `true` if we haven't taught a diagnostic with this code already.
+    /// The caller must then teach the user about such a diagnostic.
+    ///
+    /// Used to suppress emitting the same error multiple times with extended explanation when
+    /// calling `-Zteach`.
+    pub fn must_teach(&self, code: &DiagnosticId) -> bool {
+        self.inner.borrow_mut().must_teach(code)
+    }
+
+    pub fn force_print_diagnostic(&self, db: Diagnostic) {
+        self.inner.borrow_mut().force_print_diagnostic(db)
+    }
+
+    pub fn emit_diagnostic(&self, diagnostic: &Diagnostic) {
+        self.inner.borrow_mut().emit_diagnostic(diagnostic)
+    }
+
+    fn emit_diag_at_span(&self, mut diag: Diagnostic, sp: impl Into<MultiSpan>) {
+        let mut inner = self.inner.borrow_mut();
+        inner.emit_diagnostic(diag.set_span(sp));
+    }
+
+    pub fn emit_artifact_notification(&self, path: &Path, artifact_type: &str) {
+        self.inner.borrow_mut().emit_artifact_notification(path, artifact_type)
+    }
+
+    pub fn delay_as_bug(&self, diagnostic: Diagnostic) {
+        self.inner.borrow_mut().delay_as_bug(diagnostic)
+    }
+}
+
+impl HandlerInner {
+    fn must_teach(&mut self, code: &DiagnosticId) -> bool {
+        self.taught_diagnostics.insert(code.clone())
+    }
+
+    fn force_print_diagnostic(&mut self, db: Diagnostic) {
+        self.emitter.emit_diagnostic(&db);
+    }
+
+    /// Emit all stashed diagnostics.
+    fn emit_stashed_diagnostics(&mut self) {
+        let diags = self.stashed_diagnostics.drain(..).map(|x| x.1).collect::<Vec<_>>();
+        diags.iter().for_each(|diag| self.emit_diagnostic(diag));
+    }
+
+    fn emit_diagnostic(&mut self, diagnostic: &Diagnostic) {
+        if diagnostic.cancelled() {
+            return;
+        }
+
+        if diagnostic.level == Warning && !self.flags.can_emit_warnings {
+            return;
+        }
+
+        (*TRACK_DIAGNOSTICS)(diagnostic);
+
+        if let Some(ref code) = diagnostic.code {
+            self.emitted_diagnostic_codes.insert(code.clone());
+        }
+
+        let already_emitted = |this: &mut Self| {
+            use std::hash::Hash;
+            let mut hasher = StableHasher::new();
+            diagnostic.hash(&mut hasher);
+            let diagnostic_hash = hasher.finish();
+            !this.emitted_diagnostics.insert(diagnostic_hash)
+        };
+
+        // Only emit the diagnostic if we've been asked to deduplicate and
+        // haven't already emitted an equivalent diagnostic.
+        if !(self.flags.deduplicate_diagnostics && already_emitted(self)) {
+            self.emitter.emit_diagnostic(diagnostic);
+            if diagnostic.is_error() {
+                self.deduplicated_err_count += 1;
+            } else if diagnostic.level == Warning {
+                self.deduplicated_warn_count += 1;
+            }
+        }
+        if diagnostic.is_error() {
+            self.bump_err_count();
+        }
+    }
+
+    fn emit_artifact_notification(&mut self, path: &Path, artifact_type: &str) {
+        self.emitter.emit_artifact_notification(path, artifact_type);
+    }
+
+    fn treat_err_as_bug(&self) -> bool {
+        self.flags.treat_err_as_bug.map(|c| self.err_count() >= c).unwrap_or(false)
+    }
+
+    fn print_error_count(&mut self, registry: &Registry) {
+        self.emit_stashed_diagnostics();
+
+        let warnings = match self.deduplicated_warn_count {
+            0 => String::new(),
+            1 => "1 warning emitted".to_string(),
+            count => format!("{} warnings emitted", count),
+        };
+        let errors = match self.deduplicated_err_count {
+            0 => String::new(),
+            1 => "aborting due to previous error".to_string(),
+            count => format!("aborting due to {} previous errors", count),
+        };
+        if self.treat_err_as_bug() {
+            return;
+        }
+
+        match (errors.len(), warnings.len()) {
+            (0, 0) => return,
+            (0, _) => self.emit_diagnostic(&Diagnostic::new(Level::Warning, &warnings)),
+            (_, 0) => {
+                let _ = self.fatal(&errors);
+            }
+            (_, _) => {
+                let _ = self.fatal(&format!("{}; {}", &errors, &warnings));
+            }
+        }
+
+        let can_show_explain = self.emitter.should_show_explain();
+        let are_there_diagnostics = !self.emitted_diagnostic_codes.is_empty();
+        if can_show_explain && are_there_diagnostics {
+            let mut error_codes = self
+                .emitted_diagnostic_codes
+                .iter()
+                .filter_map(|x| match &x {
+                    DiagnosticId::Error(s) => {
+                        if let Ok(Some(_explanation)) = registry.try_find_description(s) {
+                            Some(s.clone())
+                        } else {
+                            None
+                        }
+                    }
+                    _ => None,
+                })
+                .collect::<Vec<_>>();
+            if !error_codes.is_empty() {
+                error_codes.sort();
+                if error_codes.len() > 1 {
+                    let limit = if error_codes.len() > 9 { 9 } else { error_codes.len() };
+                    self.failure(&format!(
+                        "Some errors have detailed explanations: {}{}",
+                        error_codes[..limit].join(", "),
+                        if error_codes.len() > 9 { "..." } else { "." }
+                    ));
+                    self.failure(&format!(
+                        "For more information about an error, try \
+                         `rustc --explain {}`.",
+                        &error_codes[0]
+                    ));
+                } else {
+                    self.failure(&format!(
+                        "For more information about this error, try \
+                         `rustc --explain {}`.",
+                        &error_codes[0]
+                    ));
+                }
+            }
+        }
+    }
+
+    fn err_count(&self) -> usize {
+        self.err_count + self.stashed_diagnostics.len()
+    }
+
+    fn has_errors(&self) -> bool {
+        self.err_count() > 0
+    }
+    fn has_errors_or_delayed_span_bugs(&self) -> bool {
+        self.has_errors() || !self.delayed_span_bugs.is_empty()
+    }
+
+    fn abort_if_errors(&mut self) {
+        self.emit_stashed_diagnostics();
+
+        if self.has_errors() {
+            FatalError.raise();
+        }
+    }
+
+    fn span_bug(&mut self, sp: impl Into<MultiSpan>, msg: &str) -> ! {
+        self.emit_diag_at_span(Diagnostic::new(Bug, msg), sp);
+        panic!(ExplicitBug);
+    }
+
+    fn emit_diag_at_span(&mut self, mut diag: Diagnostic, sp: impl Into<MultiSpan>) {
+        self.emit_diagnostic(diag.set_span(sp));
+    }
+
+    #[track_caller]
+    fn delay_span_bug(&mut self, sp: impl Into<MultiSpan>, msg: &str) {
+        // This is technically `self.treat_err_as_bug()` but `delay_span_bug` is called before
+        // incrementing `err_count` by one, so we need to +1 the comparing.
+        // FIXME: Would be nice to increment err_count in a more coherent way.
+        if self.flags.treat_err_as_bug.map(|c| self.err_count() + 1 >= c).unwrap_or(false) {
+            // FIXME: don't abort here if report_delayed_bugs is off
+            self.span_bug(sp, msg);
+        }
+        let mut diagnostic = Diagnostic::new(Level::Bug, msg);
+        diagnostic.set_span(sp.into());
+        diagnostic.note(&format!("delayed at {}", std::panic::Location::caller()));
+        self.delay_as_bug(diagnostic)
+    }
+
+    fn failure(&mut self, msg: &str) {
+        self.emit_diagnostic(&Diagnostic::new(FailureNote, msg));
+    }
+
+    fn fatal(&mut self, msg: &str) -> FatalError {
+        self.emit_error(Fatal, msg);
+        FatalError
+    }
+
+    fn err(&mut self, msg: &str) {
+        self.emit_error(Error, msg);
+    }
+
+    /// Emit an error; level should be `Error` or `Fatal`.
+    fn emit_error(&mut self, level: Level, msg: &str) {
+        if self.treat_err_as_bug() {
+            self.bug(msg);
+        }
+        self.emit_diagnostic(&Diagnostic::new(level, msg));
+    }
+
+    fn bug(&mut self, msg: &str) -> ! {
+        self.emit_diagnostic(&Diagnostic::new(Bug, msg));
+        panic!(ExplicitBug);
+    }
+
+    fn delay_as_bug(&mut self, diagnostic: Diagnostic) {
+        if self.flags.report_delayed_bugs {
+            self.emit_diagnostic(&diagnostic);
+        }
+        self.delayed_span_bugs.push(diagnostic);
+    }
+
+    fn bump_err_count(&mut self) {
+        self.err_count += 1;
+        self.panic_if_treat_err_as_bug();
+    }
+
+    fn panic_if_treat_err_as_bug(&self) {
+        if self.treat_err_as_bug() {
+            let s = match (self.err_count(), self.flags.treat_err_as_bug.unwrap_or(0)) {
+                (0, _) => return,
+                (1, 1) => "aborting due to `-Z treat-err-as-bug=1`".to_string(),
+                (1, _) => return,
+                (count, as_bug) => format!(
+                    "aborting after {} errors due to `-Z treat-err-as-bug={}`",
+                    count, as_bug,
+                ),
+            };
+            panic!(s);
+        }
+    }
+}
+
+#[derive(Copy, PartialEq, Clone, Hash, Debug, Encodable, Decodable)]
+pub enum Level {
+    Bug,
+    Fatal,
+    Error,
+    Warning,
+    Note,
+    Help,
+    Cancelled,
+    FailureNote,
+}
+
+impl fmt::Display for Level {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.to_str().fmt(f)
+    }
+}
+
+impl Level {
+    fn color(self) -> ColorSpec {
+        let mut spec = ColorSpec::new();
+        match self {
+            Bug | Fatal | Error => {
+                spec.set_fg(Some(Color::Red)).set_intense(true);
+            }
+            Warning => {
+                spec.set_fg(Some(Color::Yellow)).set_intense(cfg!(windows));
+            }
+            Note => {
+                spec.set_fg(Some(Color::Green)).set_intense(true);
+            }
+            Help => {
+                spec.set_fg(Some(Color::Cyan)).set_intense(true);
+            }
+            FailureNote => {}
+            Cancelled => unreachable!(),
+        }
+        spec
+    }
+
+    pub fn to_str(self) -> &'static str {
+        match self {
+            Bug => "error: internal compiler error",
+            Fatal | Error => "error",
+            Warning => "warning",
+            Note => "note",
+            Help => "help",
+            FailureNote => "failure-note",
+            Cancelled => panic!("Shouldn't call on cancelled error"),
+        }
+    }
+
+    pub fn is_failure_note(&self) -> bool {
+        match *self {
+            FailureNote => true,
+            _ => false,
+        }
+    }
+}
+
+#[macro_export]
+macro_rules! pluralize {
+    ($x:expr) => {
+        if $x != 1 { "s" } else { "" }
+    };
+}
+
+// Useful type to use with `Result<>` indicate that an error has already
+// been reported to the user, so no need to continue checking.
+#[derive(Clone, Copy, Debug, Encodable, Decodable, Hash, PartialEq, Eq)]
+pub struct ErrorReported;
+
+rustc_data_structures::impl_stable_hash_via_hash!(ErrorReported);