Start migration for LintDiagnostic items by adding API and migrating LinkerOutput lint

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -18,18 +18,18 @@ use rustc_attr_parsing::eval_config_entry;
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::temp_dir::MaybeTempDir;
-use rustc_errors::{DiagCtxtHandle, LintDiagnostic};
+use rustc_errors::DiagCtxtHandle;
 use rustc_fs_util::{TempDirBuilder, fix_windows_verbatim_for_gcc, try_canonicalize};
 use rustc_hir::attrs::NativeLibKind;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
-use rustc_macros::LintDiagnostic;
+use rustc_macros::Diagnostic;
 use rustc_metadata::fs::{METADATA_FILENAME, copy_to_stdout, emit_wrapper_file};
 use rustc_metadata::{
     EncodedMetadata, NativeLibSearchFallback, find_native_static_library,
     walk_native_lib_search_dirs,
 };
 use rustc_middle::bug;
-use rustc_middle::lint::lint_level;
+use rustc_middle::lint::diag_lint_level;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols::SymbolExportKind;
@@ -662,7 +662,7 @@ fn link_dwarf_object(sess: &Session, cg_results: &CodegenResults, executable_out
     }
 }
 
-#[derive(LintDiagnostic)]
+#[derive(Diagnostic)]
 #[diag("{$inner}")]
 /// Translating this is kind of useless. We don't pass translation flags to the linker, so we'd just
 /// end up with inconsistent languages within the same diagnostic.
@@ -938,9 +938,7 @@ fn link_natively(
 
             let level = codegen_results.crate_info.lint_levels.linker_messages;
             let lint = |msg| {
-                lint_level(sess, LINKER_MESSAGES, level, None, |diag| {
-                    LinkerOutput { inner: msg }.decorate_lint(diag)
-                })
+                diag_lint_level(sess, LINKER_MESSAGES, level, None, LinkerOutput { inner: msg });
             };
 
             if !prog.stderr.is_empty() {

compiler/rustc_error_messages/src/lib.rs

@@ -316,10 +316,18 @@ impl MultiSpan {
         MultiSpan { primary_spans: vec, span_labels: vec![] }
     }
 
+    pub fn push_primary_span(&mut self, primary_span: Span) {
+        self.primary_spans.push(primary_span);
+    }
+
     pub fn push_span_label(&mut self, span: Span, label: impl Into<DiagMessage>) {
         self.span_labels.push((span, label.into()));
     }
 
+    pub fn push_span_diag(&mut self, span: Span, diag: DiagMessage) {
+        self.span_labels.push((span, diag));
+    }
+
     /// Selects the first primary span (if any).
     pub fn primary_span(&self) -> Option<Span> {
         self.primary_spans.first().cloned()
@@ -386,6 +394,11 @@ impl MultiSpan {
         span_labels
     }
 
+    /// Returns the span labels as contained by `MultiSpan`.
+    pub fn span_labels_raw(&self) -> &[(Span, DiagMessage)] {
+        &self.span_labels
+    }
+
     /// Returns `true` if any of the span labels is displayable.
     pub fn has_span_labels(&self) -> bool {
         self.span_labels.iter().any(|(sp, _)| !sp.is_dummy())

compiler/rustc_middle/src/lint.rs

@@ -2,7 +2,7 @@ use std::cmp;
 
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sorted_map::SortedMap;
-use rustc_errors::{Diag, MultiSpan};
+use rustc_errors::{Diag, Diagnostic, MultiSpan};
 use rustc_hir::{HirId, ItemLocalId};
 use rustc_lint_defs::EditionFcw;
 use rustc_macros::{Decodable, Encodable, HashStable};
@@ -472,3 +472,205 @@ pub fn lint_level(
     }
     lint_level_impl(sess, lint, level, span, Box::new(decorate))
 }
+
+/// The innermost function for emitting lints implementing the [`trait@Diagnostic`] trait.
+///
+/// If you are looking to implement a lint, look for higher level functions,
+/// for example:
+///
+/// - [`TyCtxt::emit_node_span_lint`]
+/// - [`TyCtxt::node_span_lint`]
+/// - [`TyCtxt::emit_node_lint`]
+/// - [`TyCtxt::node_lint`]
+/// - `LintContext::opt_span_lint`
+///
+/// This function will replace `lint_level` once all `LintDiagnostic` items have been migrated to
+/// `Diagnostic`.
+#[track_caller]
+pub fn diag_lint_level<'a, D: Diagnostic<'a, ()> + 'a>(
+    sess: &'a Session,
+    lint: &'static Lint,
+    level: LevelAndSource,
+    span: Option<MultiSpan>,
+    decorate: D,
+) {
+    // Avoid codegen bloat from monomorphization by immediately doing dyn dispatch of `decorate` to
+    // the "real" work.
+    #[track_caller]
+    fn diag_lint_level_impl<'a>(
+        sess: &'a Session,
+        lint: &'static Lint,
+        level: LevelAndSource,
+        span: Option<MultiSpan>,
+        decorate: Box<
+            dyn FnOnce(rustc_errors::DiagCtxtHandle<'a>, rustc_errors::Level) -> Diag<'a, ()> + 'a,
+        >,
+    ) {
+        let LevelAndSource { level, lint_id, src } = level;
+
+        // Check for future incompatibility lints and issue a stronger warning.
+        let future_incompatible = lint.future_incompatible;
+
+        let has_future_breakage = future_incompatible.map_or(
+            // Default allow lints trigger too often for testing.
+            sess.opts.unstable_opts.future_incompat_test && lint.default_level != Level::Allow,
+            |incompat| incompat.report_in_deps,
+        );
+
+        // Convert lint level to error level.
+        let err_level = match level {
+            Level::Allow => {
+                if has_future_breakage {
+                    rustc_errors::Level::Allow
+                } else {
+                    return;
+                }
+            }
+            Level::Expect => {
+                // This case is special as we actually allow the lint itself in this context, but
+                // we can't return early like in the case for `Level::Allow` because we still
+                // need the lint diagnostic to be emitted to `rustc_error::DiagCtxtInner`.
+                //
+                // We can also not mark the lint expectation as fulfilled here right away, as it
+                // can still be cancelled in the decorate function. All of this means that we simply
+                // create a `Diag` and continue as we would for warnings.
+                rustc_errors::Level::Expect
+            }
+            Level::ForceWarn => rustc_errors::Level::ForceWarning,
+            Level::Warn => rustc_errors::Level::Warning,
+            Level::Deny | Level::Forbid => rustc_errors::Level::Error,
+        };
+        // Finally, run `decorate`. `decorate` can call `trimmed_path_str` (directly or indirectly),
+        // so we need to make sure when we do call `decorate` that the diagnostic is eventually
+        // emitted or we'll get a `must_produce_diag` ICE.
+        //
+        // When is a diagnostic *eventually* emitted? Well, that is determined by 2 factors:
+        // 1. If the corresponding `rustc_errors::Level` is beyond warning, i.e. `ForceWarning(_)`
+        //    or `Error`, then the diagnostic will be emitted regardless of CLI options.
+        // 2. If the corresponding `rustc_errors::Level` is warning, then that can be affected by
+        //    `-A warnings` or `--cap-lints=xxx` on the command line. In which case, the diagnostic
+        //    will be emitted if `can_emit_warnings` is true.
+        let skip = err_level == rustc_errors::Level::Warning && !sess.dcx().can_emit_warnings();
+
+        let disable_suggestions = if let Some(ref span) = span
+            // If this code originates in a foreign macro, aka something that this crate
+            // did not itself author, then it's likely that there's nothing this crate
+            // can do about it. We probably want to skip the lint entirely.
+            && span.primary_spans().iter().any(|s| s.in_external_macro(sess.source_map()))
+        {
+            true
+        } else {
+            false
+        };
+
+        let mut err: Diag<'_, ()> = if !skip {
+            decorate(sess.dcx(), err_level)
+        } else {
+            Diag::new(sess.dcx(), err_level, "")
+        };
+        if let Some(span) = span
+            && err.span.primary_span().is_none()
+        {
+            // We can't use `err.span()` because it overwrites the labels, so we need to do it manually.
+            for primary in span.primary_spans() {
+                err.span.push_primary_span(*primary);
+            }
+            for (label_span, label) in span.span_labels_raw() {
+                err.span.push_span_diag(*label_span, label.clone());
+            }
+        }
+        if let Some(lint_id) = lint_id {
+            err.lint_id(lint_id);
+        }
+
+        if disable_suggestions {
+            // Any suggestions made here are likely to be incorrect, so anything we
+            // emit shouldn't be automatically fixed by rustfix.
+            err.disable_suggestions();
+
+            // If this is a future incompatible that is not an edition fixing lint
+            // it'll become a hard error, so we have to emit *something*. Also,
+            // if this lint occurs in the expansion of a macro from an external crate,
+            // allow individual lints to opt-out from being reported.
+            let incompatible = future_incompatible.is_some_and(|f| f.reason.edition().is_none());
+
+            if !incompatible && !lint.report_in_external_macro {
+                err.cancel();
+
+                // Don't continue further, since we don't want to have
+                // `diag_span_note_once` called for a diagnostic that isn't emitted.
+                return;
+            }
+        }
+
+        err.is_lint(lint.name_lower(), has_future_breakage);
+        // Lint diagnostics that are covered by the expect level will not be emitted outside
+        // the compiler. It is therefore not necessary to add any information for the user.
+        // This will therefore directly call the decorate function which will in turn emit
+        // the diagnostic.
+        if let Level::Expect = level {
+            err.emit();
+            return;
+        }
+
+        if let Some(future_incompatible) = future_incompatible {
+            let explanation = match future_incompatible.reason {
+                FutureIncompatibilityReason::FutureReleaseError(_) => {
+                    "this was previously accepted by the compiler but is being phased out; \
+                         it will become a hard error in a future release!"
+                        .to_owned()
+                }
+                FutureIncompatibilityReason::FutureReleaseSemanticsChange(_) => {
+                    "this will change its meaning in a future release!".to_owned()
+                }
+                FutureIncompatibilityReason::EditionError(EditionFcw { edition, .. }) => {
+                    let current_edition = sess.edition();
+                    format!(
+                        "this is accepted in the current edition (Rust {current_edition}) but is a hard error in Rust {edition}!"
+                    )
+                }
+                FutureIncompatibilityReason::EditionSemanticsChange(EditionFcw {
+                    edition, ..
+                }) => {
+                    format!("this changes meaning in Rust {edition}")
+                }
+                FutureIncompatibilityReason::EditionAndFutureReleaseError(EditionFcw {
+                    edition,
+                    ..
+                }) => {
+                    format!(
+                        "this was previously accepted by the compiler but is being phased out; \
+                         it will become a hard error in Rust {edition} and in a future release in all editions!"
+                    )
+                }
+                FutureIncompatibilityReason::EditionAndFutureReleaseSemanticsChange(
+                    EditionFcw { edition, .. },
+                ) => {
+                    format!(
+                        "this changes meaning in Rust {edition} and in a future release in all editions!"
+                    )
+                }
+                FutureIncompatibilityReason::Custom(reason, _) => reason.to_owned(),
+                FutureIncompatibilityReason::Unreachable => unreachable!(),
+            };
+
+            if future_incompatible.explain_reason {
+                err.warn(explanation);
+            }
+
+            let citation =
+                format!("for more information, see {}", future_incompatible.reason.reference());
+            err.note(citation);
+        }
+
+        explain_lint_level_source(sess, lint, level, src, &mut err);
+        err.emit();
+    }
+    diag_lint_level_impl(
+        sess,
+        lint,
+        level,
+        span,
+        Box::new(move |dcx, level| decorate.into_diag(dcx, level)),
+    );
+}