Rollup merge of #121382 - nnethercote:rework-untranslatable_diagnostic-lint, r=davidtwco

Rework `untranslatable_diagnostic` lint

Currently it only checks calls to functions marked with `#[rustc_lint_diagnostics]`. This PR changes it to check calls to any function with an `impl Into<{D,Subd}iagnosticMessage>` parameter. This greatly improves its coverage and doesn't rely on people remembering to add `#[rustc_lint_diagnostics]`. It also lets us add `#[rustc_lint_diagnostics]` to a number of functions that don't have an `impl Into<{D,Subd}iagnosticMessage>`, such as `Diag::span`.

r? ``@davidtwco``

compiler/rustc_expand/src/base.rs

@@ -1493,6 +1493,8 @@ fn pretty_printing_compatibility_hack(item: &Item, sess: &Session) -> bool {
                             };
 
                             if crate_matches {
+                                // FIXME: make this translatable
+                                #[allow(rustc::untranslatable_diagnostic)]
                                 sess.psess.buffer_lint_with_diagnostic(
                                         PROC_MACRO_BACK_COMPAT,
                                         item.ident.span,

compiler/rustc_expand/src/config.rs

@@ -239,6 +239,7 @@ impl<'a> StripUnconfigured<'a> {
     /// Gives a compiler warning when the `cfg_attr` contains no attributes and
     /// is in the original source file. Gives a compiler error if the syntax of
     /// the attribute is incorrect.
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     pub(crate) fn expand_cfg_attr(&self, attr: &Attribute, recursive: bool) -> Vec<Attribute> {
         let Some((cfg_predicate, expanded_attrs)) =
             rustc_parse::parse_cfg_attr(attr, &self.sess.psess)
@@ -273,6 +274,7 @@ impl<'a> StripUnconfigured<'a> {
         }
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn expand_cfg_attr_item(
         &self,
         attr: &Attribute,
@@ -371,6 +373,7 @@ impl<'a> StripUnconfigured<'a> {
     }
 
     /// If attributes are not allowed on expressions, emit an error for `attr`
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     #[instrument(level = "trace", skip(self))]
     pub(crate) fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
         if self.features.is_some_and(|features| !features.stmt_expr_attributes)
@@ -384,7 +387,6 @@ impl<'a> StripUnconfigured<'a> {
             );
 
             if attr.is_doc_comment() {
-                #[allow(rustc::untranslatable_diagnostic)]
                 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
             }
 

compiler/rustc_expand/src/expand.rs

@@ -783,6 +783,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         })
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn gate_proc_macro_attr_item(&self, span: Span, item: &Annotatable) {
         let kind = match item {
             Annotatable::Item(_)
@@ -825,6 +826,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         }
 
         impl<'ast, 'a> Visitor<'ast> for GateProcMacroInput<'a> {
+            #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
             fn visit_item(&mut self, item: &'ast ast::Item) {
                 match &item.kind {
                     ItemKind::Mod(_, mod_kind)
@@ -1689,6 +1691,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
 
     // Detect use of feature-gated or invalid attributes on macro invocations
     // since they will not be detected after macro expansion.
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn check_attributes(&self, attrs: &[ast::Attribute], call: &ast::MacCall) {
         let features = self.cx.ecfg.features;
         let mut attrs = attrs.iter().peekable();

compiler/rustc_expand/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(associated_type_defaults)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
+#![feature(lint_reasons)]
 #![feature(macro_metavar_expr)]
 #![feature(map_try_insert)]
 #![feature(proc_macro_diagnostic)]

compiler/rustc_expand/src/proc_macro_server.rs

@@ -517,6 +517,9 @@ impl server::FreeFunctions for Rustc<'_, '_> {
             Diag::new(&self.psess().dcx, diagnostic.level.to_internal(), message);
         diag.span(MultiSpan::from_spans(diagnostic.spans));
         for child in diagnostic.children {
+            // This message comes from another diagnostic, and we are just reconstructing the
+            // diagnostic, so there's no need for translation.
+            #[allow(rustc::untranslatable_diagnostic)]
             diag.sub(child.level.to_internal(), child.message, MultiSpan::from_spans(child.spans));
         }
         diag.emit();

compiler/rustc_expand/src/tests.rs

@@ -178,6 +178,7 @@ impl<T: Write> Write for Shared<T> {
     }
 }
 
+#[allow(rustc::untranslatable_diagnostic)] // no translation needed for tests
 fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &str) {
     create_default_session_globals_then(|| {
         let (handler, source_map, output) = create_test_handler();
@@ -192,7 +193,6 @@ fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &
             println!("text: {:?}", source_map.span_to_snippet(span));
         }
 
-        #[allow(rustc::untranslatable_diagnostic)]
         handler.span_err(msp, "foo");
 
         assert!(