1 files changed, 616 insertions, 0 deletions
diff --git a/compiler/rustc_errors/src/diagnostic_builder.rs b/compiler/rustc_errors/src/diagnostic_builder.rs
new file mode 100644
index 000000000..9e68ee282
--- /dev/null
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@@ -0,0 +1,616 @@
+use crate::diagnostic::IntoDiagnosticArg;
+use crate::{
+    Diagnostic, DiagnosticId, DiagnosticMessage, DiagnosticStyledString, ErrorGuaranteed,
+    SubdiagnosticMessage,
+};
+use crate::{Handler, Level, MultiSpan, StashKey};
+use rustc_lint_defs::Applicability;
+
+use rustc_span::Span;
+use std::borrow::Cow;
+use std::fmt::{self, Debug};
+use std::marker::PhantomData;
+use std::ops::{Deref, DerefMut};
+use std::thread::panicking;
+use tracing::debug;
+
+/// Used for emitting structured error messages and other diagnostic information.
+///
+/// If there is some state in a downstream crate you would like to
+/// access in the methods of `DiagnosticBuilder` here, consider
+/// extending `HandlerFlags`, accessed via `self.handler.flags`.
+#[must_use]
+#[derive(Clone)]
+pub struct DiagnosticBuilder<'a, G: EmissionGuarantee> {
+    inner: DiagnosticBuilderInner<'a>,
+    _marker: PhantomData<G>,
+}
+
+/// This type exists only for `DiagnosticBuilder::forget_guarantee`, because it:
+/// 1. lacks the `G` parameter and therefore `DiagnosticBuilder<G1>` can be
+///    converted into `DiagnosticBuilder<G2>` while reusing the `inner` field
+/// 2. can implement the `Drop` "bomb" instead of `DiagnosticBuilder`, as it
+///    contains all of the data (`state` + `diagnostic`) of `DiagnosticBuilder`
+///
+/// The `diagnostic` field is not `Copy` and can't be moved out of whichever
+/// type implements the `Drop` "bomb", but because of the above two facts, that
+/// never needs to happen - instead, the whole `inner: DiagnosticBuilderInner`
+/// can be moved out of a `DiagnosticBuilder` and into another.
+#[must_use]
+#[derive(Clone)]
+struct DiagnosticBuilderInner<'a> {
+    state: DiagnosticBuilderState<'a>,
+
+    /// `Diagnostic` is a large type, and `DiagnosticBuilder` is often used as a
+    /// return value, especially within the frequently-used `PResult` type.
+    /// In theory, return value optimization (RVO) should avoid unnecessary
+    /// copying. In practice, it does not (at the time of writing).
+    diagnostic: Box<Diagnostic>,
+}
+
+#[derive(Clone)]
+enum DiagnosticBuilderState<'a> {
+    /// Initial state of a `DiagnosticBuilder`, before `.emit()` or `.cancel()`.
+    ///
+    /// The `Diagnostic` will be emitted through this `Handler`.
+    Emittable(&'a Handler),
+
+    /// State of a `DiagnosticBuilder`, after `.emit()` or *during* `.cancel()`.
+    ///
+    /// The `Diagnostic` will be ignored when calling `.emit()`, and it can be
+    /// assumed that `.emit()` was previously called, to end up in this state.
+    ///
+    /// While this is also used by `.cancel()`, this state is only observed by
+    /// the `Drop` `impl` of `DiagnosticBuilderInner`, as `.cancel()` takes
+    /// `self` by-value specifically to prevent any attempts to `.emit()`.
+    ///
+    // FIXME(eddyb) currently this doesn't prevent extending the `Diagnostic`,
+    // despite that being potentially lossy, if important information is added
+    // *after* the original `.emit()` call.
+    AlreadyEmittedOrDuringCancellation,
+}
+
+// `DiagnosticBuilderState` should be pointer-sized.
+rustc_data_structures::static_assert_size!(
+    DiagnosticBuilderState<'_>,
+    std::mem::size_of::<&Handler>()
+);
+
+/// Trait for types that `DiagnosticBuilder::emit` can return as a "guarantee"
+/// (or "proof") token that the emission happened.
+pub trait EmissionGuarantee: Sized {
+    /// Implementation of `DiagnosticBuilder::emit`, fully controlled by each
+    /// `impl` of `EmissionGuarantee`, to make it impossible to create a value
+    /// of `Self` without actually performing the emission.
+    #[track_caller]
+    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self;
+}
+
+/// Private module for sealing the `IsError` helper trait.
+mod sealed_level_is_error {
+    use crate::Level;
+
+    /// Sealed helper trait for statically checking that a `Level` is an error.
+    pub(crate) trait IsError<const L: Level> {}
+
+    impl IsError<{ Level::Bug }> for () {}
+    impl IsError<{ Level::DelayedBug }> for () {}
+    impl IsError<{ Level::Fatal }> for () {}
+    // NOTE(eddyb) `Level::Error { lint: true }` is also an error, but lints
+    // don't need error guarantees, as their levels are always dynamic.
+    impl IsError<{ Level::Error { lint: false } }> for () {}
+}
+
+impl<'a> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    /// Convenience function for internal use, clients should use one of the
+    /// `struct_*` methods on [`Handler`].
+    pub(crate) fn new_guaranteeing_error<M: Into<DiagnosticMessage>, const L: Level>(
+        handler: &'a Handler,
+        message: M,
+    ) -> Self
+    where
+        (): sealed_level_is_error::IsError<L>,
+    {
+        Self {
+            inner: DiagnosticBuilderInner {
+                state: DiagnosticBuilderState::Emittable(handler),
+                diagnostic: Box::new(Diagnostic::new_with_code(L, None, message)),
+            },
+            _marker: PhantomData,
+        }
+    }
+
+    /// Discard the guarantee `.emit()` would return, in favor of having the
+    /// type `DiagnosticBuilder<'a, ()>`. This may be necessary whenever there
+    /// is a common codepath handling both errors and warnings.
+    pub fn forget_guarantee(self) -> DiagnosticBuilder<'a, ()> {
+        DiagnosticBuilder { inner: self.inner, _marker: PhantomData }
+    }
+}
+
+// FIXME(eddyb) make `ErrorGuaranteed` impossible to create outside `.emit()`.
+impl EmissionGuarantee for ErrorGuaranteed {
+    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
+        match db.inner.state {
+            // First `.emit()` call, the `&Handler` is still available.
+            DiagnosticBuilderState::Emittable(handler) => {
+                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
+
+                let guar = handler.emit_diagnostic(&mut db.inner.diagnostic);
+
+                // Only allow a guarantee if the `level` wasn't switched to a
+                // non-error - the field isn't `pub`, but the whole `Diagnostic`
+                // can be overwritten with a new one, thanks to `DerefMut`.
+                assert!(
+                    db.inner.diagnostic.is_error(),
+                    "emitted non-error ({:?}) diagnostic \
+                     from `DiagnosticBuilder<ErrorGuaranteed>`",
+                    db.inner.diagnostic.level,
+                );
+                guar.unwrap()
+            }
+            // `.emit()` was previously called, disallowed from repeating it,
+            // but can take advantage of the previous `.emit()`'s guarantee
+            // still being applicable (i.e. as a form of idempotency).
+            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {
+                // Only allow a guarantee if the `level` wasn't switched to a
+                // non-error - the field isn't `pub`, but the whole `Diagnostic`
+                // can be overwritten with a new one, thanks to `DerefMut`.
+                assert!(
+                    db.inner.diagnostic.is_error(),
+                    "`DiagnosticBuilder<ErrorGuaranteed>`'s diagnostic \
+                     became non-error ({:?}), after original `.emit()`",
+                    db.inner.diagnostic.level,
+                );
+                ErrorGuaranteed::unchecked_claim_error_was_emitted()
+            }
+        }
+    }
+}
+
+impl<'a> DiagnosticBuilder<'a, ()> {
+    /// Convenience function for internal use, clients should use one of the
+    /// `struct_*` methods on [`Handler`].
+    pub(crate) fn new<M: Into<DiagnosticMessage>>(
+        handler: &'a Handler,
+        level: Level,
+        message: M,
+    ) -> Self {
+        let diagnostic = Diagnostic::new_with_code(level, None, message);
+        Self::new_diagnostic(handler, diagnostic)
+    }
+
+    /// Creates a new `DiagnosticBuilder` with an already constructed
+    /// diagnostic.
+    pub(crate) fn new_diagnostic(handler: &'a Handler, diagnostic: Diagnostic) -> Self {
+        debug!("Created new diagnostic");
+        Self {
+            inner: DiagnosticBuilderInner {
+                state: DiagnosticBuilderState::Emittable(handler),
+                diagnostic: Box::new(diagnostic),
+            },
+            _marker: PhantomData,
+        }
+    }
+}
+
+// FIXME(eddyb) should there be a `Option<ErrorGuaranteed>` impl as well?
+impl EmissionGuarantee for () {
+    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
+        match db.inner.state {
+            // First `.emit()` call, the `&Handler` is still available.
+            DiagnosticBuilderState::Emittable(handler) => {
+                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
+
+                handler.emit_diagnostic(&mut db.inner.diagnostic);
+            }
+            // `.emit()` was previously called, disallowed from repeating it.
+            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
+        }
+    }
+}
+
+impl<'a> DiagnosticBuilder<'a, !> {
+    /// Convenience function for internal use, clients should use one of the
+    /// `struct_*` methods on [`Handler`].
+    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)
+    }
+
+    /// Creates a new `DiagnosticBuilder` with an already constructed
+    /// diagnostic.
+    pub(crate) fn new_diagnostic_fatal(handler: &'a Handler, diagnostic: Diagnostic) -> Self {
+        debug!("Created new diagnostic");
+        Self {
+            inner: DiagnosticBuilderInner {
+                state: DiagnosticBuilderState::Emittable(handler),
+                diagnostic: Box::new(diagnostic),
+            },
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl EmissionGuarantee for ! {
+    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
+        match db.inner.state {
+            // First `.emit()` call, the `&Handler` is still available.
+            DiagnosticBuilderState::Emittable(handler) => {
+                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
+
+                handler.emit_diagnostic(&mut db.inner.diagnostic);
+            }
+            // `.emit()` was previously called, disallowed from repeating it.
+            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
+        }
+        // Then fatally error, returning `!`
+        crate::FatalError.raise()
+    }
+}
+
+/// In general, the `DiagnosticBuilder` uses deref to allow access to
+/// the fields and methods of the embedded `diagnostic` in a
+/// transparent way. *However,* many of the methods are intended to
+/// be used in a chained way, and hence ought to return `self`. In
+/// that case, we can't just naively forward to the method on the
+/// `diagnostic`, because the return type would be a `&Diagnostic`
+/// instead of a `&DiagnosticBuilder<'a>`. This `forward!` macro makes
+/// it easy to declare such methods on the builder.
+macro_rules! forward {
+    // Forward pattern for &mut self -> &mut Self
+    (
+        $(#[$attrs:meta])*
+        pub fn $n:ident(&mut self, $($name:ident: $ty:ty),* $(,)?) -> &mut Self
+    ) => {
+        $(#[$attrs])*
+        #[doc = concat!("See [`Diagnostic::", stringify!($n), "()`].")]
+        pub fn $n(&mut self, $($name: $ty),*) -> &mut Self {
+            self.inner.diagnostic.$n($($name),*);
+            self
+        }
+    };
+}
+
+impl<G: EmissionGuarantee> Deref for DiagnosticBuilder<'_, G> {
+    type Target = Diagnostic;
+
+    fn deref(&self) -> &Diagnostic {
+        &self.inner.diagnostic
+    }
+}
+
+impl<G: EmissionGuarantee> DerefMut for DiagnosticBuilder<'_, G> {
+    fn deref_mut(&mut self) -> &mut Diagnostic {
+        &mut self.inner.diagnostic
+    }
+}
+
+impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
+    /// Emit the diagnostic.
+    #[track_caller]
+    pub fn emit(&mut self) -> G {
+        G::diagnostic_builder_emit_producing_guarantee(self)
+    }
+
+    /// Emit the diagnostic unless `delay` is true,
+    /// in which case the emission will be delayed as a bug.
+    ///
+    /// See `emit` and `delay_as_bug` for details.
+    #[track_caller]
+    pub fn emit_unless(&mut self, delay: bool) -> G {
+        if delay {
+            self.downgrade_to_delayed_bug();
+        }
+        self.emit()
+    }
+
+    /// Cancel the diagnostic (a structured diagnostic must either be emitted or
+    /// cancelled or it will panic when dropped).
+    ///
+    /// This method takes `self` by-value to disallow calling `.emit()` on it,
+    /// which may be expected to *guarantee* the emission of an error, either
+    /// at the time of the call, or through a prior `.emit()` call.
+    pub fn cancel(mut self) {
+        self.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
+        drop(self);
+    }
+
+    /// Stashes diagnostic for possible later improvement in a different,
+    /// later stage of the compiler. The diagnostic can be accessed with
+    /// the provided `span` and `key` through [`Handler::steal_diagnostic()`].
+    ///
+    /// As with `buffer`, this is unless the handler has disabled such buffering.
+    pub fn stash(self, span: Span, key: StashKey) {
+        if let Some((diag, handler)) = self.into_diagnostic() {
+            handler.stash_diagnostic(span, key, diag);
+        }
+    }
+
+    /// Converts the builder to a `Diagnostic` for later emission,
+    /// unless handler has disabled such buffering, or `.emit()` was called.
+    pub fn into_diagnostic(mut self) -> Option<(Diagnostic, &'a Handler)> {
+        let handler = match self.inner.state {
+            // No `.emit()` calls, the `&Handler` is still available.
+            DiagnosticBuilderState::Emittable(handler) => handler,
+            // `.emit()` was previously called, nothing we can do.
+            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {
+                return None;
+            }
+        };
+
+        if handler.flags.dont_buffer_diagnostics || handler.flags.treat_err_as_bug.is_some() {
+            self.emit();
+            return None;
+        }
+
+        // Take the `Diagnostic` by replacing it with a dummy.
+        let dummy = Diagnostic::new(Level::Allow, DiagnosticMessage::Str("".to_string()));
+        let diagnostic = std::mem::replace(&mut *self.inner.diagnostic, dummy);
+
+        // Disable the ICE on `Drop`.
+        self.cancel();
+
+        // Logging here is useful to help track down where in logs an error was
+        // actually emitted.
+        debug!("buffer: diagnostic={:?}", diagnostic);
+
+        Some((diagnostic, handler))
+    }
+
+    /// Buffers the diagnostic for later emission,
+    /// unless handler has disabled such buffering.
+    pub fn buffer(self, buffered_diagnostics: &mut Vec<Diagnostic>) {
+        buffered_diagnostics.extend(self.into_diagnostic().map(|(diag, _)| diag));
+    }
+
+    /// Delay emission of this diagnostic as a bug.
+    ///
+    /// This can be useful in contexts where an error indicates a bug but
+    /// typically this only happens when other compilation errors have already
+    /// happened. In those cases this can be used to defer emission of this
+    /// diagnostic as a bug in the compiler only if no other errors have been
+    /// emitted.
+    ///
+    /// In the meantime, though, callsites are required to deal with the "bug"
+    /// locally in whichever way makes the most sense.
+    #[track_caller]
+    pub fn delay_as_bug(&mut self) {
+        self.downgrade_to_delayed_bug();
+        self.emit();
+    }
+
+    forward!(
+        #[track_caller]
+        pub fn downgrade_to_delayed_bug(&mut self,) -> &mut Self
+    );
+
+    forward!(
+    /// Appends a labeled span to the diagnostic.
+    ///
+    /// Labels are used to convey additional context for the diagnostic's primary span. They will
+    /// be shown together with the original diagnostic's span, *not* with spans added by
+    /// `span_note`, `span_help`, etc. Therefore, if the primary span is not displayable (because
+    /// the span is `DUMMY_SP` or the source code isn't found), labels will not be displayed
+    /// either.
+    ///
+    /// Implementation-wise, the label span is pushed onto the [`MultiSpan`] that was created when
+    /// the diagnostic was constructed. However, the label span is *not* considered a
+    /// ["primary span"][`MultiSpan`]; only the `Span` supplied when creating the diagnostic is
+    /// primary.
+    pub fn span_label(&mut self, span: Span, label: impl Into<SubdiagnosticMessage>) -> &mut Self);
+
+    forward!(
+    /// Labels all the given spans with the provided label.
+    /// See [`Diagnostic::span_label()`] for more information.
+    pub fn span_labels(
+        &mut self,
+        spans: impl IntoIterator<Item = Span>,
+        label: impl AsRef<str>,
+    ) -> &mut Self);
+
+    forward!(pub fn note_expected_found(
+        &mut self,
+        expected_label: &dyn fmt::Display,
+        expected: DiagnosticStyledString,
+        found_label: &dyn fmt::Display,
+        found: DiagnosticStyledString,
+    ) -> &mut Self);
+
+    forward!(pub fn note_expected_found_extra(
+        &mut self,
+        expected_label: &dyn fmt::Display,
+        expected: DiagnosticStyledString,
+        found_label: &dyn fmt::Display,
+        found: DiagnosticStyledString,
+        expected_extra: &dyn fmt::Display,
+        found_extra: &dyn fmt::Display,
+    ) -> &mut Self);
+
+    forward!(pub fn note_unsuccessful_coercion(
+        &mut self,
+        expected: DiagnosticStyledString,
+        found: DiagnosticStyledString,
+    ) -> &mut Self);
+
+    forward!(pub fn note(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
+    forward!(pub fn note_once(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
+    forward!(pub fn span_note(
+        &mut self,
+        sp: impl Into<MultiSpan>,
+        msg: impl Into<SubdiagnosticMessage>,
+    ) -> &mut Self);
+    forward!(pub fn span_note_once(
+        &mut self,
+        sp: impl Into<MultiSpan>,
+        msg: impl Into<SubdiagnosticMessage>,
+    ) -> &mut Self);
+    forward!(pub fn warn(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
+    forward!(pub fn span_warn(
+        &mut self,
+        sp: impl Into<MultiSpan>,
+        msg: impl Into<SubdiagnosticMessage>,
+    ) -> &mut Self);
+    forward!(pub fn help(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
+    forward!(pub fn span_help(
+        &mut self,
+        sp: impl Into<MultiSpan>,
+        msg: impl Into<SubdiagnosticMessage>,
+    ) -> &mut Self);
+    forward!(pub fn help_use_latest_edition(&mut self,) -> &mut Self);
+    forward!(pub fn set_is_lint(&mut self,) -> &mut Self);
+
+    forward!(pub fn disable_suggestions(&mut self,) -> &mut Self);
+    forward!(pub fn clear_suggestions(&mut self,) -> &mut Self);
+
+    forward!(pub fn multipart_suggestion(
+        &mut self,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: Vec<(Span, String)>,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn multipart_suggestion_verbose(
+        &mut self,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: Vec<(Span, String)>,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn tool_only_multipart_suggestion(
+        &mut self,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: Vec<(Span, String)>,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn span_suggestion(
+        &mut self,
+        sp: Span,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: impl ToString,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn span_suggestions(
+        &mut self,
+        sp: Span,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestions: impl Iterator<Item = String>,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn multipart_suggestions(
+        &mut self,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestions: impl Iterator<Item = Vec<(Span, String)>>,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn span_suggestion_short(
+        &mut self,
+        sp: Span,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: impl ToString,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn span_suggestion_verbose(
+        &mut self,
+        sp: Span,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: impl ToString,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn span_suggestion_hidden(
+        &mut self,
+        sp: Span,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: impl ToString,
+        applicability: Applicability,
+    ) -> &mut Self);
+    forward!(pub fn tool_only_span_suggestion(
+        &mut self,
+        sp: Span,
+        msg: impl Into<SubdiagnosticMessage>,
+        suggestion: impl ToString,
+        applicability: Applicability,
+    ) -> &mut Self);
+
+    forward!(pub fn set_primary_message(&mut self, msg: impl Into<DiagnosticMessage>) -> &mut Self);
+    forward!(pub fn set_span(&mut self, sp: impl Into<MultiSpan>) -> &mut Self);
+    forward!(pub fn code(&mut self, s: DiagnosticId) -> &mut Self);
+    forward!(pub fn set_arg(
+        &mut self,
+        name: impl Into<Cow<'static, str>>,
+        arg: impl IntoDiagnosticArg,
+    ) -> &mut Self);
+
+    forward!(pub fn subdiagnostic(
+        &mut self,
+        subdiagnostic: impl crate::AddSubdiagnostic
+    ) -> &mut Self);
+}
+
+impl<G: EmissionGuarantee> Debug for DiagnosticBuilder<'_, G> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.diagnostic.fmt(f)
+    }
+}
+
+/// Destructor bomb - a `DiagnosticBuilder` must be either emitted or cancelled
+/// or we emit a bug.
+impl Drop for DiagnosticBuilderInner<'_> {
+    fn drop(&mut self) {
+        match self.state {
+            // No `.emit()` or `.cancel()` calls.
+            DiagnosticBuilderState::Emittable(handler) => {
+                if !panicking() {
+                    handler.emit_diagnostic(&mut Diagnostic::new(
+                        Level::Bug,
+                        DiagnosticMessage::Str(
+                            "the following error was constructed but not emitted".to_string(),
+                        ),
+                    ));
+                    handler.emit_diagnostic(&mut self.diagnostic);
+                    panic!();
+                }
+            }
+            // `.emit()` was previously called, or maybe we're during `.cancel()`.
+            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
+        }
+    }
+}
+
+#[macro_export]
+macro_rules! struct_span_err {
+    ($session:expr, $span:expr, $code:ident, $($message:tt)*) => ({
+        $session.struct_span_err_with_code(
+            $span,
+            &format!($($message)*),
+            $crate::error_code!($code),
+        )
+    })
+}
+
+#[macro_export]
+macro_rules! error_code {
+    ($code:ident) => {{ $crate::DiagnosticId::Error(stringify!($code).to_owned()) }};
+}
+
+/// Wrapper around a `DiagnosticBuilder` for creating lints.
+pub struct LintDiagnosticBuilder<'a, G: EmissionGuarantee>(DiagnosticBuilder<'a, G>);
+
+impl<'a, G: EmissionGuarantee> LintDiagnosticBuilder<'a, G> {
+    #[rustc_lint_diagnostics]
+    /// Return the inner `DiagnosticBuilder`, first setting the primary message to `msg`.
+    pub fn build(mut self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'a, G> {
+        self.0.set_primary_message(msg);
+        self.0.set_is_lint();
+        self.0
+    }
+
+    /// Create a `LintDiagnosticBuilder` from some existing `DiagnosticBuilder`.
+    pub fn new(err: DiagnosticBuilder<'a, G>) -> LintDiagnosticBuilder<'a, G> {
+        LintDiagnosticBuilder(err)
+    }
+}
+
+impl<'a> LintDiagnosticBuilder<'a, ErrorGuaranteed> {
+    pub fn forget_guarantee(self) -> LintDiagnosticBuilder<'a, ()> {
+        LintDiagnosticBuilder(self.0.forget_guarantee())
+    }
+}