Remove unused #[must_use]

compiler/rustc_expand/src/expand.rs

@@ -2157,6 +2157,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                             attr_name,
                             macro_name: pprust::path_to_string(&call.path),
                             invoc_span: call.path.span,
+                            attr_span: attr.span,
                         },
                     );
                 }

compiler/rustc_lint/messages.ftl

@@ -982,6 +982,7 @@ lint_unused_allocation_mut = unnecessary allocation, use `&mut` instead
 
 lint_unused_builtin_attribute = unused attribute `{$attr_name}`
     .note = the built-in attribute `{$attr_name}` will be ignored, since it's applied to the macro invocation `{$macro_name}`
+    .suggestion = remove the attribute
 
 lint_unused_closure =
     unused {$pre}{$count ->

compiler/rustc_lint/src/early/diagnostics.rs

@@ -205,8 +205,14 @@ pub fn decorate_builtin_lint(
             }
             .decorate_lint(diag);
         }
-        BuiltinLintDiag::UnusedBuiltinAttribute { attr_name, macro_name, invoc_span } => {
-            lints::UnusedBuiltinAttribute { invoc_span, attr_name, macro_name }.decorate_lint(diag);
+        BuiltinLintDiag::UnusedBuiltinAttribute {
+            attr_name,
+            macro_name,
+            invoc_span,
+            attr_span,
+        } => {
+            lints::UnusedBuiltinAttribute { invoc_span, attr_name, macro_name, attr_span }
+                .decorate_lint(diag);
         }
         BuiltinLintDiag::TrailingMacro(is_trailing, name) => {
             lints::TrailingMacro { is_trailing, name }.decorate_lint(diag);

compiler/rustc_lint/src/lints.rs

@@ -2935,9 +2935,10 @@ pub(crate) struct RawPrefix {
 pub(crate) struct UnusedBuiltinAttribute {
     #[note]
     pub invoc_span: Span,
-
     pub attr_name: Symbol,
     pub macro_name: String,
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
+    pub attr_span: Span,
 }
 
 #[derive(LintDiagnostic)]

compiler/rustc_lint_defs/src/lib.rs

@@ -647,6 +647,7 @@ pub enum BuiltinLintDiag {
         attr_name: Symbol,
         macro_name: String,
         invoc_span: Span,
+        attr_span: Span,
     },
     PatternsInFnsWithoutBody {
         span: Span,

compiler/rustc_passes/messages.ftl

@@ -510,6 +510,7 @@ passes_must_not_suspend =
 
 passes_must_use_no_effect =
     `#[must_use]` has no effect when applied to {$article} {$target}
+    .suggestion = remove the attribute
 
 passes_no_link =
     attribute should be applied to an `extern crate` item

compiler/rustc_passes/src/check_attr.rs

@@ -1621,7 +1621,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             UNUSED_ATTRIBUTES,
             hir_id,
             attr_span,
-            errors::MustUseNoEffect { article, target },
+            errors::MustUseNoEffect { article, target, attr_span },
         );
     }
 

compiler/rustc_passes/src/errors.rs

@@ -469,6 +469,8 @@ pub(crate) struct FfiConstInvalidTarget {
 pub(crate) struct MustUseNoEffect {
     pub article: &'static str,
     pub target: rustc_hir::Target,
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
+    pub attr_span: Span,
 }
 
 #[derive(Diagnostic)]

tests/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs

@@ -71,6 +71,7 @@
 //~^^ WARN this was previously accepted by the compiler
 #![must_use]
 //~^ WARN `#[must_use]` has no effect
+//~| HELP remove the attribute
 // see issue-43106-gating-of-stable.rs
 // see issue-43106-gating-of-unstable.rs
 // see issue-43106-gating-of-deprecated.rs
@@ -599,16 +600,20 @@ mod deprecated {
 }
 
 #[must_use] //~ WARN `#[must_use]` has no effect
+//~^ HELP remove the attribute
 mod must_use {
     mod inner { #![must_use] } //~ WARN `#[must_use]` has no effect
+    //~^ HELP remove the attribute
 
     #[must_use] fn f() { }
 
     #[must_use] struct S;
 
     #[must_use] type T = S; //~ WARN `#[must_use]` has no effect
+    //~^ HELP remove the attribute
 
     #[must_use] impl S { } //~ WARN `#[must_use]` has no effect
+    //~^ HELP remove the attribute
 }
 
 #[windows_subsystem = "windows"]