Auto merge of #126996 - oli-obk:do_not_count_errors, r=nnethercote

Automatically taint InferCtxt when errors are emitted

r? `@nnethercote`

Basically `InferCtxt::dcx` now returns a `DiagCtxt` that refers back to the `Cell<Option<ErrorGuaranteed>>` of the `InferCtxt` and thus when invoking `Diag::emit`, and the diagnostic is an error, we taint the `InferCtxt` directly.

That change on its own has no effect at all, because `InferCtxt` already tracks whether errors have been emitted by recording the global error count when it gets opened, and checking at the end whether the count changed. So I removed that error count check, which had a bit of fallout that I immediately fixed by invoking `InferCtxt::dcx` instead of `TyCtxt::dcx` in a bunch of places.

The remaining new errors are because an error was reported in another query, and never bubbled up. I think they are minor enough for this to be ok, and sometimes it actually improves diagnostics, by not silencing useful diagnostics anymore.

fixes #126485 (cc `@olafes)`

There are more improvements we can do (like tainting in hir ty lowering), but I would rather do that in follow up PRs, because it requires some refactorings.

compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs

@@ -88,7 +88,7 @@ impl<'tcx> InferCtxt<'tcx> {
         found_args: Vec<ArgKind>,
         is_closure: bool,
         closure_arg_span: Option<Span>,
-    ) -> Diag<'tcx> {
+    ) -> Diag<'_> {
         let kind = if is_closure { "closure" } else { "function" };
 
         let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -241,8 +241,8 @@ pub fn suggest_restriction<'tcx, G: EmissionGuarantee>(
     }
 }
 
-#[extension(pub trait TypeErrCtxtExt<'tcx>)]
-impl<'tcx> TypeErrCtxt<'_, 'tcx> {
+#[extension(pub trait TypeErrCtxtExt<'a, 'tcx>)]
+impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
     fn suggest_restricting_param_bound(
         &self,
         err: &mut Diag<'_>,
@@ -1845,7 +1845,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
     fn point_at_returns_when_relevant(
         &self,
-        err: &mut Diag<'tcx>,
+        err: &mut Diag<'_>,
         obligation: &PredicateObligation<'tcx>,
     ) {
         match obligation.cause.code().peel_derives() {
@@ -1884,7 +1884,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         cause: &ObligationCauseCode<'tcx>,
         found_node: Option<Node<'_>>,
         param_env: ty::ParamEnv<'tcx>,
-    ) -> Diag<'tcx> {
+    ) -> Diag<'a> {
         pub(crate) fn build_fn_sig_ty<'tcx>(
             infcx: &InferCtxt<'tcx>,
             trait_ref: ty::TraitRef<'tcx>,
@@ -2104,7 +2104,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     fn note_conflicting_closure_bounds(
         &self,
         cause: &ObligationCauseCode<'tcx>,
-        err: &mut Diag<'tcx>,
+        err: &mut Diag<'_>,
     ) {
         // First, look for an `WhereClauseInExpr`, which means we can get
         // the uninstantiated predicate list of the called function. And check

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -82,8 +82,8 @@ pub fn suggest_new_overflow_limit<'tcx, G: EmissionGuarantee>(
     ));
 }
 
-#[extension(pub trait TypeErrCtxtExt<'tcx>)]
-impl<'tcx> TypeErrCtxt<'_, 'tcx> {
+#[extension(pub trait TypeErrCtxtExt<'a, 'tcx>)]
+impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
     fn report_fulfillment_errors(
         &self,
         mut errors: Vec<FulfillmentError<'tcx>>,
@@ -228,7 +228,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         cause: OverflowCause<'tcx>,
         span: Span,
         suggest_increasing_limit: bool,
-    ) -> Diag<'tcx> {
+    ) -> Diag<'a> {
         fn with_short_path<'tcx, T>(tcx: TyCtxt<'tcx>, value: T) -> String
         where
             T: fmt::Display + Print<'tcx, FmtPrinter<'tcx, 'tcx>>,
@@ -1101,7 +1101,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 && let ty::FnPtr(sig) = by_ref_captures.kind()
                 && !sig.skip_binder().output().is_unit()
             {
-                let mut err = self.tcx.dcx().create_err(AsyncClosureNotFn {
+                let mut err = self.dcx().create_err(AsyncClosureNotFn {
                     span: self.tcx.def_span(closure_def_id),
                     kind: expected_kind.as_str(),
                 });
@@ -1351,7 +1351,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         &self,
         ty: Ty<'tcx>,
         obligation: &PredicateObligation<'tcx>,
-    ) -> Diag<'tcx> {
+    ) -> Diag<'a> {
         let span = obligation.cause.span;
 
         let mut diag = match ty.kind() {
@@ -1445,8 +1445,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     }
 }
 
-#[extension(pub(super) trait InferCtxtPrivExt<'tcx>)]
-impl<'tcx> TypeErrCtxt<'_, 'tcx> {
+#[extension(pub(super) trait InferCtxtPrivExt<'a, 'tcx>)]
+impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
     fn can_match_trait(
         &self,
         goal: ty::TraitPredicate<'tcx>,
@@ -2884,7 +2884,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             self.suggest_unsized_bound_if_applicable(err, obligation);
             if let Some(span) = err.span.primary_span()
                 && let Some(mut diag) =
-                    self.tcx.dcx().steal_non_err(span, StashKey::AssociatedTypeSuggestion)
+                    self.dcx().steal_non_err(span, StashKey::AssociatedTypeSuggestion)
                 && let Ok(ref mut s1) = err.suggestions
                 && let Ok(ref mut s2) = diag.suggestions
             {
@@ -3379,7 +3379,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         found_kind: ty::ClosureKind,
         kind: ty::ClosureKind,
         trait_prefix: &'static str,
-    ) -> Diag<'tcx> {
+    ) -> Diag<'a> {
         let closure_span = self.tcx.def_span(closure_def_id);
 
         let mut err = ClosureKindMismatch {
@@ -3422,7 +3422,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         found_trait_ref: ty::TraitRef<'tcx>,
         expected_trait_ref: ty::TraitRef<'tcx>,
         terr: TypeError<'tcx>,
-    ) -> Diag<'tcx> {
+    ) -> Diag<'a> {
         let self_ty = found_trait_ref.self_ty();
         let (cause, terr) = if let ty::Closure(def_id, _) = self_ty.kind() {
             (
@@ -3473,7 +3473,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         span: Span,
         found_trait_ref: ty::TraitRef<'tcx>,
         expected_trait_ref: ty::TraitRef<'tcx>,
-    ) -> Result<Diag<'tcx>, ErrorGuaranteed> {
+    ) -> Result<Diag<'a>, ErrorGuaranteed> {
         let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
         let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
 
@@ -3553,7 +3553,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     })
                     .unwrap_or((found_span, None, found));
 
-                self.report_arg_count_mismatch(
+                self.infcx.report_arg_count_mismatch(
                     span,
                     closure_span,
                     expected,
@@ -3569,7 +3569,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         &self,
         obligation: &PredicateObligation<'tcx>,
         span: Span,
-    ) -> Result<Diag<'tcx>, ErrorGuaranteed> {
+    ) -> Result<Diag<'a>, ErrorGuaranteed> {
         if !self.tcx.features().generic_const_exprs {
             let guar = self
                 .dcx()