Auto merge of rust-lang#119606 - nnethercote:consuming-emit, r=oli-obk

Consuming `emit`

This PR makes `DiagnosticBuilder::emit` consuming, i.e. take `self` instead of `&mut self`. This is good because it doesn't make sense to emit a diagnostic twice.

This requires some changes to `DiagnosticBuilder` method changing -- every existing non-consuming chaining method gets a new consuming partner with a `_mv` suffix -- but permits a host of beneficial follow-up changes: more concise code through more chaining, removal of redundant diagnostic construction API methods, and removal of machinery to track the possibility of a diagnostic being emitted multiple times.

r? `@compiler-errors`

Author: bors

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -23,7 +23,7 @@ macro_rules! gate {
     ($visitor:expr, $feature:ident, $span:expr, $explain:expr, $help:expr) => {{
         if !$visitor.features.$feature && !$span.allows_unstable(sym::$feature) {
             feature_err(&$visitor.sess.parse_sess, sym::$feature, $span, $explain)
-                .help($help)
+                .help_mv($help)
                 .emit();
         }
     }};

compiler/rustc_attr/src/session_diagnostics.rs

@@ -54,13 +54,12 @@ pub(crate) struct UnknownMetaItem<'a> {
 impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for UnknownMetaItem<'_> {
     fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'a, G> {
         let expected = self.expected.iter().map(|name| format!("`{name}`")).collect::<Vec<_>>();
-        let mut diag = DiagnosticBuilder::new(dcx, level, fluent::attr_unknown_meta_item);
-        diag.span(self.span);
-        diag.code(error_code!(E0541));
-        diag.arg("item", self.item);
-        diag.arg("expected", expected.join(", "));
-        diag.span_label(self.span, fluent::attr_label);
-        diag
+        DiagnosticBuilder::new(dcx, level, fluent::attr_unknown_meta_item)
+            .span_mv(self.span)
+            .code_mv(error_code!(E0541))
+            .arg_mv("item", self.item)
+            .arg_mv("expected", expected.join(", "))
+            .span_label_mv(self.span, fluent::attr_label)
     }
 }
 

compiler/rustc_borrowck/src/borrowck_errors.rs

@@ -31,17 +31,15 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         borrow_span: Span,
         borrow_desc: &str,
     ) -> DiagnosticBuilder<'tcx> {
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             span,
             E0503,
             "cannot use {} because it was mutably borrowed",
             desc,
-        );
-
-        err.span_label(borrow_span, format!("{borrow_desc} is borrowed here"));
-        err.span_label(span, format!("use of borrowed {borrow_desc}"));
-        err
+        )
+        .span_label_mv(borrow_span, format!("{borrow_desc} is borrowed here"))
+        .span_label_mv(span, format!("use of borrowed {borrow_desc}"))
     }
 
     pub(crate) fn cannot_mutably_borrow_multiply(
@@ -238,17 +236,15 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         borrow_span: Span,
         desc: &str,
     ) -> DiagnosticBuilder<'cx> {
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             span,
             E0506,
             "cannot assign to {} because it is borrowed",
             desc,
-        );
-
-        err.span_label(borrow_span, format!("{desc} is borrowed here"));
-        err.span_label(span, format!("{desc} is assigned to here but it was already borrowed"));
-        err
+        )
+        .span_label_mv(borrow_span, format!("{desc} is borrowed here"))
+        .span_label_mv(span, format!("{desc} is assigned to here but it was already borrowed"))
     }
 
     pub(crate) fn cannot_reassign_immutable(
@@ -287,32 +283,30 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
             (&ty::Slice(_), _) => "slice",
             _ => span_bug!(move_from_span, "this path should not cause illegal move"),
         };
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             move_from_span,
             E0508,
             "cannot move out of type `{}`, a non-copy {}",
             ty,
             type_name,
-        );
-        err.span_label(move_from_span, "cannot move out of here");
-        err
+        )
+        .span_label_mv(move_from_span, "cannot move out of here")
     }
 
     pub(crate) fn cannot_move_out_of_interior_of_drop(
         &self,
         move_from_span: Span,
         container_ty: Ty<'_>,
     ) -> DiagnosticBuilder<'cx> {
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             move_from_span,
             E0509,
             "cannot move out of type `{}`, which implements the `Drop` trait",
             container_ty,
-        );
-        err.span_label(move_from_span, "cannot move out of here");
-        err
+        )
+        .span_label_mv(move_from_span, "cannot move out of here")
     }
 
     pub(crate) fn cannot_act_on_moved_value(
@@ -352,18 +346,17 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         immutable_section: &str,
         action: &str,
     ) -> DiagnosticBuilder<'tcx> {
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             mutate_span,
             E0510,
             "cannot {} {} in {}",
             action,
             immutable_place,
             immutable_section,
-        );
-        err.span_label(mutate_span, format!("cannot {action}"));
-        err.span_label(immutable_span, format!("value is immutable in {immutable_section}"));
-        err
+        )
+        .span_label_mv(mutate_span, format!("cannot {action}"))
+        .span_label_mv(immutable_span, format!("value is immutable in {immutable_section}"))
     }
 
     pub(crate) fn cannot_borrow_across_coroutine_yield(
@@ -372,14 +365,13 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         yield_span: Span,
     ) -> DiagnosticBuilder<'tcx> {
         let coroutine_kind = self.body.coroutine.as_ref().unwrap().coroutine_kind;
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             span,
             E0626,
             "borrow may still be in use when {coroutine_kind:#} yields",
-        );
-        err.span_label(yield_span, "possible yield occurs here");
-        err
+        )
+        .span_label_mv(yield_span, "possible yield occurs here")
     }
 
     pub(crate) fn cannot_borrow_across_destructor(
@@ -409,22 +401,19 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         reference_desc: &str,
         path_desc: &str,
     ) -> DiagnosticBuilder<'tcx> {
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             span,
             E0515,
             "cannot {RETURN} {REFERENCE} {LOCAL}",
             RETURN = return_kind,
             REFERENCE = reference_desc,
             LOCAL = path_desc,
-        );
-
-        err.span_label(
+        )
+        .span_label_mv(
             span,
             format!("{return_kind}s a {reference_desc} data owned by the current function"),
-        );
-
-        err
+        )
     }
 
     pub(crate) fn cannot_capture_in_long_lived_closure(
@@ -435,16 +424,15 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         capture_span: Span,
         scope: &str,
     ) -> DiagnosticBuilder<'tcx> {
-        let mut err = struct_span_err!(
+        struct_span_err!(
             self.dcx(),
             closure_span,
             E0373,
             "{closure_kind} may outlive the current {scope}, but it borrows {borrowed_path}, \
              which is owned by the current {scope}",
-        );
-        err.span_label(capture_span, format!("{borrowed_path} is borrowed here"))
-            .span_label(closure_span, format!("may outlive borrowed value {borrowed_path}"));
-        err
+        )
+        .span_label_mv(capture_span, format!("{borrowed_path} is borrowed here"))
+        .span_label_mv(closure_span, format!("may outlive borrowed value {borrowed_path}"))
     }
 
     pub(crate) fn thread_local_value_does_not_live_long_enough(

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2218,15 +2218,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             drop_span, borrow_span
         );
 
-        let mut err = self.thread_local_value_does_not_live_long_enough(borrow_span);
-
-        err.span_label(
-            borrow_span,
-            "thread-local variables cannot be borrowed beyond the end of the function",
-        );
-        err.span_label(drop_span, "end of enclosing function is here");
-
-        err
+        self.thread_local_value_does_not_live_long_enough(borrow_span)
+            .span_label_mv(
+                borrow_span,
+                "thread-local variables cannot be borrowed beyond the end of the function",
+            )
+            .span_label_mv(drop_span, "end of enclosing function is here")
     }
 
     #[instrument(level = "debug", skip(self))]

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -329,15 +329,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         if let PlaceRef { local, projection: [] } = deref_base {
             let decl = &self.body.local_decls[local];
             if decl.is_ref_for_guard() {
-                let mut err = self.cannot_move_out_of(
-                    span,
-                    &format!("`{}` in pattern guard", self.local_names[local].unwrap()),
-                );
-                err.note(
-                    "variables bound in patterns cannot be moved from \
+                return self
+                    .cannot_move_out_of(
+                        span,
+                        &format!("`{}` in pattern guard", self.local_names[local].unwrap()),
+                    )
+                    .note_mv(
+                        "variables bound in patterns cannot be moved from \
                      until after the end of the pattern guard",
-                );
-                return err;
+                    );
             } else if decl.is_ref_to_static() {
                 return self.report_cannot_move_from_static(move_place, span);
             }
@@ -381,15 +381,12 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     closure_kind_ty, closure_kind, place_description,
                 );
 
-                let mut diag = self.cannot_move_out_of(span, &place_description);
-
-                diag.span_label(upvar_span, "captured outer variable");
-                diag.span_label(
-                    self.infcx.tcx.def_span(def_id),
-                    format!("captured by this `{closure_kind}` closure"),
-                );
-
-                diag
+                self.cannot_move_out_of(span, &place_description)
+                    .span_label_mv(upvar_span, "captured outer variable")
+                    .span_label_mv(
+                        self.infcx.tcx.def_span(def_id),
+                        format!("captured by this `{closure_kind}` closure"),
+                    )
             }
             _ => {
                 let source = self.borrowed_content_source(deref_base);

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -348,7 +348,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     let named_ty = self.regioncx.name_regions(self.infcx.tcx, hidden_ty);
                     let named_key = self.regioncx.name_regions(self.infcx.tcx, key);
                     let named_region = self.regioncx.name_regions(self.infcx.tcx, member_region);
-                    let mut diag = unexpected_hidden_region_diagnostic(
+                    let diag = unexpected_hidden_region_diagnostic(
                         self.infcx.tcx,
                         span,
                         named_ty,

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -421,7 +421,7 @@ fn check_opaque_type_parameter_valid(
             return Err(tcx
                 .dcx()
                 .struct_span_err(span, "non-defining opaque type use in defining scope")
-                .span_note(spans, format!("{descr} used multiple times"))
+                .span_note_mv(spans, format!("{descr} used multiple times"))
                 .emit());
         }
     }

compiler/rustc_builtin_macros/src/asm.rs

@@ -458,7 +458,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
             match expr_to_spanned_string(ecx, template_expr, msg) {
                 Ok(template_part) => template_part,
                 Err(err) => {
-                    if let Some((mut err, _)) = err {
+                    if let Some((err, _)) = err {
                         err.emit();
                     }
                     return None;
@@ -693,13 +693,14 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
         0 => {}
         1 => {
             let (sp, msg) = unused_operands.into_iter().next().unwrap();
-            let mut err = ecx.dcx().struct_span_err(sp, msg);
-            err.span_label(sp, msg);
-            err.help(format!(
-                "if this argument is intentionally unused, \
-                 consider using it in an asm comment: `\"/*{help_str} */\"`"
-            ));
-            err.emit();
+            ecx.dcx()
+                .struct_span_err(sp, msg)
+                .span_label_mv(sp, msg)
+                .help_mv(format!(
+                    "if this argument is intentionally unused, \
+                     consider using it in an asm comment: `\"/*{help_str} */\"`"
+                ))
+                .emit();
         }
         _ => {
             let mut err = ecx.dcx().struct_span_err(
@@ -747,7 +748,7 @@ pub(super) fn expand_asm<'cx>(
             };
             MacEager::expr(expr)
         }
-        Err(mut err) => {
+        Err(err) => {
             err.emit();
             DummyResult::any(sp)
         }
@@ -779,7 +780,7 @@ pub(super) fn expand_global_asm<'cx>(
                 DummyResult::any(sp)
             }
         }
-        Err(mut err) => {
+        Err(err) => {
             err.emit();
             DummyResult::any(sp)
         }

compiler/rustc_builtin_macros/src/assert.rs

@@ -22,7 +22,7 @@ pub fn expand_assert<'cx>(
 ) -> Box<dyn MacResult + 'cx> {
     let Assert { cond_expr, custom_message } = match parse_assert(cx, span, tts) {
         Ok(assert) => assert,
-        Err(mut err) => {
+        Err(err) => {
             err.emit();
             return DummyResult::any(span);
         }

compiler/rustc_builtin_macros/src/cfg.rs

@@ -28,7 +28,7 @@ pub fn expand_cfg(
             );
             MacEager::expr(cx.expr_bool(sp, matches_cfg))
         }
-        Err(mut err) => {
+        Err(err) => {
             err.emit();
             DummyResult::any(sp)
         }