Fix target list of link_section

compiler/rustc_attr_parsing/src/attributes/link_attrs.rs

@@ -467,8 +467,14 @@ impl<S: Stage> SingleAttributeParser<S> for LinkSectionParser {
     const PATH: &[Symbol] = &[sym::link_section];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const ALLOWED_TARGETS: AllowedTargets =
-        AllowedTargets::AllowListWarnRest(&[Allow(Target::Static), Allow(Target::Fn)]);
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+        Allow(Target::Static),
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+    ]);
     const TEMPLATE: AttributeTemplate = template!(
         NameValueStr: "name",
         "https://doc.rust-lang.org/reference/abi.html#the-link_section-attribute"

tests/ui/attributes/attr-on-mac-call.stderr

@@ -82,7 +82,7 @@ LL |     #[link_section = "x"]
    |     ^^^^^^^^^^^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = help: `#[link_section]` can be applied to statics and functions
+   = help: `#[link_section]` can be applied to functions and statics
 
 warning: `#[link_ordinal]` attribute cannot be used on macro calls
   --> $DIR/attr-on-mac-call.rs:33:5

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

@@ -705,6 +705,32 @@ mod link_section {
     //~| WARN previously accepted
     //~| HELP can be applied to
     //~| HELP remove the attribute
+
+    #[link_section = "1800"]
+    //~^ WARN attribute cannot be used on
+    //~| WARN previously accepted
+    //~| HELP can be applied to
+    //~| HELP remove the attribute
+    trait Tr {
+        #[link_section = "1800"]
+        fn inside_tr_no_default(&self);
+
+        #[link_section = "1800"]
+        fn inside_tr_default(&self) { }
+    }
+
+    impl S {
+        #[link_section = "1800"]
+        fn inside_abc_123(&self) { }
+    }
+
+    impl Tr for S {
+        #[link_section = "1800"]
+        fn inside_tr_no_default(&self) { }
+    }
+
+    #[link_section = "1800"]
+    fn should_always_link() { }
 }