Rewrite the untranslatable_diagnostic lint.

Currently it only checks calls to functions marked with
`#[rustc_lint_diagnostics]`. This commit changes it to check calls to
any function with a `impl Into<{D,Subd}iagnosticMessage>` parameter.
This greatly improves its coverage and doesn't rely on people
remembering to add `#[rustc_lint_diagnostics]`.

The commit also adds `#[allow(rustc::untranslatable_diagnostic)`]
attributes to places that need it that are caught by the improved lint.
These places that might be easy to convert to translatable diagnostics.

Finally, it also:
- Expands and corrects some comments.
- Does some minor formatting improvements.
- Adds missing `DecorateLint` cases to
  `tests/ui-fulldeps/internal-lints/diagnostics.rs`.

Author: nnethercote

compiler/rustc_ast_lowering/src/asm.rs

@@ -22,6 +22,7 @@ use std::collections::hash_map::Entry;
 use std::fmt::Write;
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     pub(crate) fn lower_inline_asm(
         &mut self,
         sp: Span,

compiler/rustc_ast_lowering/src/expr.rs

@@ -1499,6 +1499,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
         let is_async_gen = match self.coroutine_kind {
             Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _)) => false,

compiler/rustc_ast_lowering/src/lib.rs

@@ -2272,6 +2272,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.expr_block(block)
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
         match c.value.kind {
             ExprKind::Underscore => {

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -17,6 +17,7 @@ use crate::errors;
 macro_rules! gate {
     ($visitor:expr, $feature:ident, $span:expr, $explain:expr) => {{
         if !$visitor.features.$feature && !$span.allows_unstable(sym::$feature) {
+            #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
             feature_err(&$visitor.sess, sym::$feature, $span, $explain).emit();
         }
     }};
@@ -34,6 +35,7 @@ macro_rules! gate {
 macro_rules! gate_alt {
     ($visitor:expr, $has_feature:expr, $name:expr, $span:expr, $explain:expr) => {{
         if !$has_feature && !$span.allows_unstable($name) {
+            #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
             feature_err(&$visitor.sess, $name, $span, $explain).emit();
         }
     }};
@@ -73,6 +75,7 @@ struct PostExpansionVisitor<'a> {
 }
 
 impl<'a> PostExpansionVisitor<'a> {
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn check_abi(&self, abi: ast::StrLit, constness: ast::Const) {
         let ast::StrLit { symbol_unescaped, span, .. } = abi;
 
@@ -579,6 +582,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
                 if let Ok(snippet) = sm.span_to_snippet(span)
                     && snippet == "!"
                 {
+                    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
                     feature_err(sess, sym::never_patterns, span, "`!` patterns are experimental")
                         .emit();
                 } else {

compiler/rustc_attr/src/builtin.rs

@@ -516,6 +516,7 @@ pub struct Condition {
 }
 
 /// Tests if a cfg-pattern matches the cfg set
+#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 pub fn cfg_matches(
     cfg: &ast::MetaItem,
     sess: &Session,
@@ -566,6 +567,7 @@ fn try_gate_cfg(name: Symbol, span: Span, sess: &Session, features: Option<&Feat
     }
 }
 
+#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 fn gate_cfg(gated_cfg: &GatedCfg, cfg_span: Span, sess: &Session, features: &Features) {
     let (cfg, feature, has_feature) = gated_cfg;
     if !has_feature(features) && !cfg_span.allows_unstable(*feature) {
@@ -592,6 +594,7 @@ fn parse_version(s: Symbol) -> Option<RustcVersion> {
 
 /// Evaluate a cfg-like condition (with `any` and `all`), using `eval` to
 /// evaluate individual items.
+#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 pub fn eval_condition(
     cfg: &ast::MetaItem,
     sess: &Session,

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -1008,6 +1008,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         self.borrow_spans(span, borrow.reserve_location)
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn explain_captures(
         &mut self,
         err: &mut Diag<'_>,

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -201,6 +201,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
     // For generic associated types (GATs) which implied 'static requirement
     // from higher-ranked trait bounds (HRTB). Try to locate span of the trait
     // and the span which bounded to the trait for adding 'static lifetime suggestion
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn suggest_static_lifetime_for_gat_from_hrtb(
         &self,
         diag: &mut Diag<'_>,
@@ -822,6 +823,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
     /// LL |     fn iter_values_anon(&self) -> impl Iterator<Item=u32> + 'a {
     ///    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     /// ```
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn add_static_impl_trait_suggestion(
         &self,
         diag: &mut Diag<'_>,
@@ -972,6 +974,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         self.suggest_constrain_dyn_trait_in_impl(diag, &visitor.0, ident, self_ty);
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     #[instrument(skip(self, err), level = "debug")]
     fn suggest_constrain_dyn_trait_in_impl(
         &self,
@@ -1034,6 +1037,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         suggest_adding_lifetime_params(self.infcx.tcx, sub, ty_sup, ty_sub, diag);
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn suggest_move_on_borrowing_closure(&self, diag: &mut Diag<'_>) {
         let map = self.infcx.tcx.hir();
         let body_id = map.body_owned_by(self.mir_def_id());

compiler/rustc_const_eval/src/transform/check_consts/ops.rs

@@ -62,6 +62,7 @@ impl<'tcx> NonConstOp<'tcx> for FloatingPointOp {
         }
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
         feature_err(
             &ccx.tcx.sess,
@@ -556,6 +557,7 @@ impl<'tcx> NonConstOp<'tcx> for RawMutPtrDeref {
         Status::Unstable(sym::const_mut_refs)
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
         feature_err(
             &ccx.tcx.sess,
@@ -589,6 +591,7 @@ impl<'tcx> NonConstOp<'tcx> for StaticAccess {
         }
     }
 
+    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
         let mut err = feature_err(
             &ccx.tcx.sess,
@@ -632,6 +635,7 @@ pub mod ty {
             }
         }
 
+        #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
         fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
             feature_err(
                 &ccx.tcx.sess,

compiler/rustc_driver_impl/src/args.rs

@@ -97,6 +97,7 @@ impl Expander {
 /// **Note:** This function doesn't interpret argument 0 in any special way.
 /// If this function is intended to be used with command line arguments,
 /// `argv[0]` must be removed prior to calling it manually.
+#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 pub fn arg_expand_all(early_dcx: &EarlyDiagCtxt, at_args: &[String]) -> Vec<String> {
     let mut expander = Expander::default();
     for arg in at_args {

compiler/rustc_driver_impl/src/lib.rs

@@ -4,6 +4,7 @@
 //!
 //! This API is completely unstable and subject to change.
 
+#![allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]