Rollup merge of #145500 - JonathanBrouwer:must_use_target, r=jdonszelmann

Port must_use to the new target checking

This PR ports `must_use` to the new target checking logic
This also adds a tool-only suggestion to remove attributes on invalid targets, as to not immediately undo the work of https://github.com/rust-lang/rust/pull/145274

r? `@jdonszelmann`

4 files changed, 24 insertions, 2 deletions

diff --git a/compiler/rustc_attr_parsing/messages.ftl b/compiler/rustc_attr_parsing/messages.ftl
index 4fb66a81652..067d95a0f48 100644
--- a/compiler/rustc_attr_parsing/messages.ftl
+++ b/compiler/rustc_attr_parsing/messages.ftl
@@ -12,9 +12,11 @@ attr_parsing_empty_attribute =
 
 attr_parsing_invalid_target = `#[{$name}]` attribute cannot be used on {$target}
     .help = `#[{$name}]` can {$only}be applied to {$applied}
+    .suggestion = remove the attribute
 attr_parsing_invalid_target_lint = `#[{$name}]` attribute cannot be used on {$target}
     .warn = {-attr_parsing_previously_accepted}
     .help = `#[{$name}]` can {$only}be applied to {$applied}
+    .suggestion = remove the attribute
 
 attr_parsing_empty_confusables =
     expected at least one confusable name
diff --git a/compiler/rustc_attr_parsing/src/attributes/must_use.rs b/compiler/rustc_attr_parsing/src/attributes/must_use.rs
index b0ee3d1ba6e..eb2b39298bc 100644
--- a/compiler/rustc_attr_parsing/src/attributes/must_use.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/must_use.rs
@@ -1,10 +1,12 @@
 use rustc_errors::DiagArgValue;
 use rustc_feature::{AttributeTemplate, template};
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Symbol, sym};
 
 use crate::attributes::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{ALL_TARGETS, AcceptContext, AllowedTargets, Stage};
+use crate::context::MaybeWarn::{Allow, Error};
+use crate::context::{AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
 use crate::session_diagnostics;
 pub(crate) struct MustUseParser;
@@ -13,7 +15,21 @@ impl<S: Stage> SingleAttributeParser<S> for MustUseParser {
     const PATH: &[Symbol] = &[sym::must_use];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS); //FIXME Still checked fully in `check_attr.rs`
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+        Allow(Target::Fn),
+        Allow(Target::Enum),
+        Allow(Target::Struct),
+        Allow(Target::Union),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::ForeignFn),
+        // `impl Trait` in return position can trip
+        // `unused_must_use` if `Trait` is marked as
+        // `#[must_use]`
+        Allow(Target::Trait),
+        Error(Target::WherePredicate),
+    ]);
     const TEMPLATE: AttributeTemplate = template!(
         Word, NameValueStr: "reason",
         "https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute"
diff --git a/compiler/rustc_attr_parsing/src/lints.rs b/compiler/rustc_attr_parsing/src/lints.rs
index 733225bab59..2813fef3148 100644
--- a/compiler/rustc_attr_parsing/src/lints.rs
+++ b/compiler/rustc_attr_parsing/src/lints.rs
@@ -53,6 +53,7 @@ pub fn emit_attribute_lint<L: LintEmitter>(lint: &AttributeLint<HirId>, lint_emi
                     target: target.plural_name(),
                     applied: applied.clone(),
                     only,
+                    attr_span: *span,
                 },
             ),
     }
diff --git a/compiler/rustc_attr_parsing/src/session_diagnostics.rs b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
index c65937b35b3..aec970a3ce9 100644
--- a/compiler/rustc_attr_parsing/src/session_diagnostics.rs
+++ b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
@@ -489,6 +489,8 @@ pub(crate) struct InvalidTargetLint {
     pub target: &'static str,
     pub applied: String,
     pub only: &'static str,
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
+    pub attr_span: Span,
 }
 
 #[derive(Diagnostic)]
@@ -496,6 +498,7 @@ pub(crate) struct InvalidTargetLint {
 #[diag(attr_parsing_invalid_target)]
 pub(crate) struct InvalidTarget {
     #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
     pub span: Span,
     pub name: Symbol,
     pub target: &'static str,