rustc_errors: let DiagnosticBuilder::emit return a "guarantee of emission".

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -1068,8 +1068,9 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                             .emit();
                     }
                 }
-                let ill_formed =
-                    |span| struct_span_err!(self.r.session, span, E0466, "bad macro import").emit();
+                let ill_formed = |span| {
+                    struct_span_err!(self.r.session, span, E0466, "bad macro import").emit();
+                };
                 match attr.meta() {
                     Some(meta) => match meta.kind {
                         MetaItemKind::Word => {

compiler/rustc_resolve/src/diagnostics.rs

@@ -3,7 +3,7 @@ use std::ptr;
 use rustc_ast::{self as ast, Path};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
+use rustc_errors::{struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorReported};
 use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind};
@@ -110,7 +110,7 @@ impl<'a> Resolver<'a> {
         &self,
         span: Span,
         resolution_error: ResolutionError<'_>,
-    ) -> DiagnosticBuilder<'_> {
+    ) -> DiagnosticBuilder<'_, ErrorReported> {
         match resolution_error {
             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
                 let mut err = struct_span_err!(
@@ -624,7 +624,10 @@ impl<'a> Resolver<'a> {
         }
     }
 
-    crate fn report_vis_error(&self, vis_resolution_error: VisResolutionError<'_>) {
+    crate fn report_vis_error(
+        &self,
+        vis_resolution_error: VisResolutionError<'_>,
+    ) -> ErrorReported {
         match vis_resolution_error {
             VisResolutionError::Relative2018(span, path) => {
                 let mut err = self.session.struct_span_err(

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -12,7 +12,9 @@ use rustc_ast::{
 };
 use rustc_ast_pretty::pprust::path_segment_to_string;
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
+use rustc_errors::{
+    pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorReported,
+};
 use rustc_hir as hir;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
@@ -133,7 +135,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         span: Span,
         source: PathSource<'_>,
         res: Option<Res>,
-    ) -> (DiagnosticBuilder<'a>, Vec<ImportSuggestion>) {
+    ) -> (DiagnosticBuilder<'a, ErrorReported>, Vec<ImportSuggestion>) {
         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
         let ns = source.namespace();
         let is_expected = &|res| source.is_expected(res);
@@ -1817,7 +1819,7 @@ impl<'tcx> LifetimeContext<'_, 'tcx> {
         &self,
         spans: Vec<Span>,
         count: usize,
-    ) -> DiagnosticBuilder<'tcx> {
+    ) -> DiagnosticBuilder<'tcx, ErrorReported> {
         struct_span_err!(
             self.tcx.sess,
             spans,

compiler/rustc_resolve/src/late/lifetimes.rs

@@ -1572,6 +1572,7 @@ fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: Symbol, orig: Original, shado
             name,
             orig.kind.desc()
         )
+        .forget_guarantee()
     } else {
         // shadowing involving a label is only a warning, due to issues with
         // labels and lifetimes not being macro-hygienic.

compiler/rustc_resolve/src/lib.rs

@@ -40,7 +40,7 @@ use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_data_structures::intern::Interned;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
+use rustc_errors::{struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorReported};
 use rustc_expand::base::{DeriveResolutions, SyntaxExtension, SyntaxExtensionKind};
 use rustc_hir::def::Namespace::*;
 use rustc_hir::def::{self, CtorOf, DefKind, NonMacroAttrKind, PartialRes};
@@ -713,7 +713,7 @@ struct PrivacyError<'a> {
 }
 
 struct UseError<'a> {
-    err: DiagnosticBuilder<'a>,
+    err: DiagnosticBuilder<'a, ErrorReported>,
     /// Candidates which user could `use` to access the missing type.
     candidates: Vec<ImportSuggestion>,
     /// The `DefId` of the module to place the use-statements in.