Use chaining for DiagnosticBuilder construction and emit.

To avoid the use of a mutable local variable, and because it reads more
nicely.

Author: nnethercote

compiler/rustc_builtin_macros/src/asm.rs

@@ -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(

compiler/rustc_codegen_cranelift/src/driver/jit.rs

@@ -321,9 +321,10 @@ fn dep_symbol_lookup_fn(
             Linkage::NotLinked | Linkage::IncludedFromDylib => {}
             Linkage::Static => {
                 let name = crate_info.crate_name[&cnum];
-                let mut err = sess.dcx().struct_err(format!("Can't load static lib {}", name));
-                err.note("rustc_codegen_cranelift can only load dylibs in JIT mode.");
-                err.emit();
+                sess.dcx()
+                    .struct_err(format!("Can't load static lib {}", name))
+                    .note("rustc_codegen_cranelift can only load dylibs in JIT mode.")
+                    .emit();
             }
             Linkage::Dynamic => {
                 dylib_paths.push(src.dylib.as_ref().unwrap().0.clone());

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -303,14 +303,14 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                         // This exception needs to be kept in sync with allowing
                         // `#[target_feature]` on `main` and `start`.
                     } else if !tcx.features().target_feature_11 {
-                        let mut err = feature_err(
+                        feature_err(
                             &tcx.sess.parse_sess,
                             sym::target_feature_11,
                             attr.span,
                             "`#[target_feature(..)]` can only be applied to `unsafe` functions",
-                        );
-                        err.span_label(tcx.def_span(did), "not an `unsafe` function");
-                        err.emit();
+                        )
+                        .span_label_mv(tcx.def_span(did), "not an `unsafe` function")
+                        .emit();
                     } else {
                         check_target_feature_trait_unsafe(tcx, did, attr.span);
                     }

compiler/rustc_hir_analysis/src/astconv/generics.rs

@@ -650,9 +650,9 @@ pub(crate) fn prohibit_explicit_late_bound_lifetimes(
         if position == GenericArgPosition::Value
             && args.num_lifetime_params() != param_counts.lifetimes
         {
-            let mut err = struct_span_err!(tcx.dcx(), span, E0794, "{}", msg);
-            err.span_note(span_late, note);
-            err.emit();
+            struct_span_err!(tcx.dcx(), span, E0794, "{}", msg)
+                .span_note_mv(span_late, note)
+                .emit();
         } else {
             let mut multispan = MultiSpan::from_span(span);
             multispan.push_span_label(span_late, note);

compiler/rustc_hir_analysis/src/astconv/object_safety.rs

@@ -290,19 +290,19 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
                 if references_self {
                     let def_id = i.bottom().0.def_id();
-                    let mut err = struct_span_err!(
+                    struct_span_err!(
                         tcx.dcx(),
                         i.bottom().1,
                         E0038,
                         "the {} `{}` cannot be made into an object",
                         tcx.def_descr(def_id),
                         tcx.item_name(def_id),
-                    );
-                    err.note(
+                    )
+                    .note_mv(
                         rustc_middle::traits::ObjectSafetyViolation::SupertraitSelf(smallvec![])
                             .error_msg(),
-                    );
-                    err.emit();
+                    )
+                    .emit();
                 }
 
                 ty::ExistentialTraitRef { def_id: trait_ref.def_id, args }

compiler/rustc_hir_analysis/src/check/check.rs

@@ -1140,13 +1140,13 @@ fn check_enum(tcx: TyCtxt<'_>, def_id: LocalDefId) {
         let disr_non_unit = def.variants().iter().any(|var| !is_unit(var) && has_disr(var));
 
         if disr_non_unit || (disr_units && has_non_units) {
-            let err = struct_span_err!(
+            struct_span_err!(
                 tcx.dcx(),
                 tcx.def_span(def_id),
                 E0732,
                 "`#[repr(inttype)]` must be specified"
-            );
-            err.emit();
+            )
+            .emit();
         }
     }
 

compiler/rustc_hir_analysis/src/check/intrinsicck.rs

@@ -153,22 +153,26 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
         };
         let Some(asm_ty) = asm_ty else {
             let msg = format!("cannot use value of type `{ty}` for inline assembly");
-            let mut err = self.tcx.dcx().struct_span_err(expr.span, msg);
-            err.note(
-                "only integers, floats, SIMD vectors, pointers and function pointers \
-                 can be used as arguments for inline assembly",
-            );
-            err.emit();
+            self.tcx
+                .dcx()
+                .struct_span_err(expr.span, msg)
+                .note_mv(
+                    "only integers, floats, SIMD vectors, pointers and function pointers \
+                     can be used as arguments for inline assembly",
+                )
+                .emit();
             return None;
         };
 
         // Check that the type implements Copy. The only case where this can
         // possibly fail is for SIMD types which don't #[derive(Copy)].
         if !ty.is_copy_modulo_regions(self.tcx, self.param_env) {
             let msg = "arguments for inline assembly must be copyable";
-            let mut err = self.tcx.dcx().struct_span_err(expr.span, msg);
-            err.note(format!("`{ty}` does not implement the Copy trait"));
-            err.emit();
+            self.tcx
+                .dcx()
+                .struct_span_err(expr.span, msg)
+                .note_mv(format!("`{ty}` does not implement the Copy trait"))
+                .emit();
         }
 
         // Ideally we wouldn't need to do this, but LLVM's register allocator
@@ -183,16 +187,17 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
         if let Some((in_expr, Some(in_asm_ty))) = tied_input {
             if in_asm_ty != asm_ty {
                 let msg = "incompatible types for asm inout argument";
-                let mut err = self.tcx.dcx().struct_span_err(vec![in_expr.span, expr.span], msg);
-
                 let in_expr_ty = (self.get_operand_ty)(in_expr);
-                err.span_label(in_expr.span, format!("type `{in_expr_ty}`"));
-                err.span_label(expr.span, format!("type `{ty}`"));
-                err.note(
-                    "asm inout arguments must have the same type, \
+                self.tcx
+                    .dcx()
+                    .struct_span_err(vec![in_expr.span, expr.span], msg)
+                    .span_label_mv(in_expr.span, format!("type `{in_expr_ty}`"))
+                    .span_label_mv(expr.span, format!("type `{ty}`"))
+                    .note_mv(
+                        "asm inout arguments must have the same type, \
                     unless they are both pointers or integers of the same size",
-                );
-                err.emit();
+                    )
+                    .emit();
             }
 
             // All of the later checks have already been done on the input, so
@@ -234,13 +239,15 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
         if let Some(feature) = feature {
             if !target_features.contains(feature) {
                 let msg = format!("`{feature}` target feature is not enabled");
-                let mut err = self.tcx.dcx().struct_span_err(expr.span, msg);
-                err.note(format!(
-                    "this is required to use type `{}` with register class `{}`",
-                    ty,
-                    reg_class.name(),
-                ));
-                err.emit();
+                self.tcx
+                    .dcx()
+                    .struct_span_err(expr.span, msg)
+                    .note_mv(format!(
+                        "this is required to use type `{}` with register class `{}`",
+                        ty,
+                        reg_class.name(),
+                    ))
+                    .emit();
                 return Some(asm_ty);
             }
         }
@@ -449,14 +456,17 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
                         ty::Never | ty::Error(_) => {}
                         ty::FnDef(..) => {}
                         _ => {
-                            let mut err =
-                                self.tcx.dcx().struct_span_err(*op_sp, "invalid `sym` operand");
-                            err.span_label(
-                                self.tcx.def_span(anon_const.def_id),
-                                format!("is {} `{}`", ty.kind().article(), ty),
-                            );
-                            err.help("`sym` operands must refer to either a function or a static");
-                            err.emit();
+                            self.tcx
+                                .dcx()
+                                .struct_span_err(*op_sp, "invalid `sym` operand")
+                                .span_label_mv(
+                                    self.tcx.def_span(anon_const.def_id),
+                                    format!("is {} `{}`", ty.kind().article(), ty),
+                                )
+                                .help_mv(
+                                    "`sym` operands must refer to either a function or a static",
+                                )
+                                .emit();
                         }
                     };
                 }

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -197,11 +197,12 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) -> Result<()
             let mut res = Ok(());
             if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
                 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
-                let mut err =
-                    tcx.dcx().struct_span_err(sp, "impls of auto traits cannot be default");
-                err.span_labels(impl_.defaultness_span, "default because of this");
-                err.span_label(sp, "auto trait");
-                res = Err(err.emit());
+                res = Err(tcx
+                    .dcx()
+                    .struct_span_err(sp, "impls of auto traits cannot be default")
+                    .span_labels_mv(impl_.defaultness_span, "default because of this")
+                    .span_label_mv(sp, "auto trait")
+                    .emit());
             }
             // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
             match tcx.impl_polarity(def_id) {
@@ -489,35 +490,33 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
 
         if !unsatisfied_bounds.is_empty() {
             let plural = pluralize!(unsatisfied_bounds.len());
-            let mut err = tcx.dcx().struct_span_err(
-                gat_item_hir.span,
-                format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
-            );
-
             let suggestion = format!(
                 "{} {}",
                 gat_item_hir.generics.add_where_or_trailing_comma(),
                 unsatisfied_bounds.join(", "),
             );
-            err.span_suggestion(
-                gat_item_hir.generics.tail_span_for_predicate_suggestion(),
-                format!("add the required where clause{plural}"),
-                suggestion,
-                Applicability::MachineApplicable,
-            );
-
             let bound =
                 if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
-            err.note(format!(
-                "{bound} currently required to ensure that impls have maximum flexibility"
-            ));
-            err.note(
-                "we are soliciting feedback, see issue #87479 \
+            tcx.dcx()
+                .struct_span_err(
+                    gat_item_hir.span,
+                    format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
+                )
+                .span_suggestion_mv(
+                    gat_item_hir.generics.tail_span_for_predicate_suggestion(),
+                    format!("add the required where clause{plural}"),
+                    suggestion,
+                    Applicability::MachineApplicable,
+                )
+                .note_mv(format!(
+                    "{bound} currently required to ensure that impls have maximum flexibility"
+                ))
+                .note_mv(
+                    "we are soliciting feedback, see issue #87479 \
                  <https://github.com/rust-lang/rust/issues/87479> \
                  for more information",
-            );
-
-            err.emit();
+                )
+                .emit();
         }
     }
 }
@@ -938,8 +937,8 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(),
                 };
                 if may_suggest_feature && tcx.sess.is_nightly_build() {
                     diag.help(
-                            "add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types",
-                        );
+                        "add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types",
+                    );
                 }
 
                 Err(diag.emit())

compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs

@@ -70,17 +70,16 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
             match seen_items.entry(norm_ident) {
                 Entry::Occupied(entry) => {
                     let former = entry.get();
-                    let mut err = struct_span_err!(
+                    struct_span_err!(
                         self.tcx.dcx(),
                         span,
                         E0592,
                         "duplicate definitions with name `{}`",
                         ident,
-                    );
-                    err.span_label(span, format!("duplicate definitions for `{ident}`"));
-                    err.span_label(*former, format!("other definition for `{ident}`"));
-
-                    err.emit();
+                    )
+                    .span_label_mv(span, format!("duplicate definitions for `{ident}`"))
+                    .span_label_mv(*former, format!("other definition for `{ident}`"))
+                    .emit();
                 }
                 Entry::Vacant(entry) => {
                     entry.insert(span);

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -750,12 +750,12 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                         kind: hir::ItemKind::OpaqueTy { .. }, ..
                     }) = self.tcx.hir_node(parent_id)
                     {
-                        let mut err = self.tcx.dcx().struct_span_err(
+                        self.tcx.dcx().struct_span_err(
                             lifetime.ident.span,
                             "higher kinded lifetime bounds on nested opaque types are not supported yet",
-                        );
-                        err.span_note(self.tcx.def_span(def_id), "lifetime declared here");
-                        err.emit();
+                        )
+                        .span_note_mv(self.tcx.def_span(def_id), "lifetime declared here")
+                        .emit();
                         self.uninsert_lifetime_on_error(lifetime, def.unwrap());
                     }
                 }