Address review comments

src/librustc_lint/lib.rs

@@ -338,7 +338,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
         },
         FutureIncompatibleInfo {
             id: LintId::of(ILL_FORMED_ATTRIBUTE_INPUT),
-            reference: "issue #57321 <https://github.com/rust-lang/rust/issues/57321>",
+            reference: "issue #57571 <https://github.com/rust-lang/rust/issues/57571>",
             edition: None,
         },
         ]);

src/libsyntax/feature_gate.rs

@@ -717,6 +717,8 @@ pub enum AttributeGate {
     Ungated,
 }
 
+/// A template that the attribute input must match.
+/// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
 #[derive(Clone, Copy)]
 pub struct AttributeTemplate {
     word: bool,
@@ -725,6 +727,7 @@ pub struct AttributeTemplate {
 }
 
 impl AttributeTemplate {
+    /// Check that the given meta-item is compatible with this template.
     fn compatible(&self, meta_item_kind: &ast::MetaItemKind) -> bool {
         match meta_item_kind {
             ast::MetaItemKind::Word => self.word,
@@ -735,10 +738,10 @@ impl AttributeTemplate {
     }
 }
 
+/// A convenience macro for constructing attribute templates.
+/// E.g. `template!(Word, List: "description")` means that the attribute
+/// supports forms `#[attr]` and `#[attr(description)]`.
 macro_rules! template {
-    (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
-        word: $word, list: $list, name_value_str: $name_value_str
-    } };
     (Word) => { template!(@ true, None, None) };
     (List: $descr: expr) => { template!(@ false, Some($descr), None) };
     (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
@@ -750,6 +753,9 @@ macro_rules! template {
     (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
         template!(@ true, Some($descr1), Some($descr2))
     };
+    (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
+        word: $word, list: $list, name_value_str: $name_value_str
+    } };
 }
 
 impl AttributeGate {
@@ -1084,7 +1090,8 @@ pub const BUILTIN_ATTRIBUTES: &[(&str, AttributeType, AttributeTemplate, Attribu
                                         is an experimental feature",
                                        cfg_fn!(fundamental))),
 
-    ("proc_macro_derive", Normal, template!(List: "TraitName, attributes(name1, name2, ...)"),
+    ("proc_macro_derive", Normal, template!(List: "TraitName, \
+                                                   /*opt*/ attributes(name1, name2, ...)"),
                                        Ungated),
 
     ("rustc_copy_clone_marker", Whitelisted, template!(Word), Gated(Stability::Unstable,

src/test/ui/feature-gate/issue-43106-gating-of-inline.stderr

@@ -6,7 +6,7 @@ LL |     #[inline = "2100"] fn f() { }
    |
    = note: #[warn(ill_formed_attribute_input)] on by default
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57321 <https://github.com/rust-lang/rust/issues/57321>
+   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
 
 error[E0518]: attribute should be applied to function or closure
   --> $DIR/issue-43106-gating-of-inline.rs:11:1

src/test/ui/malformed/malformed-regressions.stderr

@@ -6,7 +6,7 @@ LL | #[doc] //~ WARN attribute must be of the form
    |
    = note: #[warn(ill_formed_attribute_input)] on by default
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57321 <https://github.com/rust-lang/rust/issues/57321>
+   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
 
 warning: attribute must be of the form `#[ignore]` or `#[ignore = "reason"]`
   --> $DIR/malformed-regressions.rs:4:1
@@ -15,7 +15,7 @@ LL | #[ignore()] //~ WARN attribute must be of the form
    | ^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57321 <https://github.com/rust-lang/rust/issues/57321>
+   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
 
 warning: attribute must be of the form `#[inline]` or `#[inline(always|never)]`
   --> $DIR/malformed-regressions.rs:5:1
@@ -24,7 +24,7 @@ LL | #[inline = ""] //~ WARN attribute must be of the form
    | ^^^^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57321 <https://github.com/rust-lang/rust/issues/57321>
+   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
 
 warning: attribute must be of the form `#[link(name = "...", /*opt*/ kind = "dylib|static|...",
                                              /*opt*/ cfg = "...")]`
@@ -34,7 +34,7 @@ LL | #[link] //~ WARN attribute must be of the form
    | ^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57321 <https://github.com/rust-lang/rust/issues/57321>
+   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
 
 warning: attribute must be of the form `#[link(name = "...", /*opt*/ kind = "dylib|static|...",
                                              /*opt*/ cfg = "...")]`
@@ -44,5 +44,5 @@ LL | #[link = ""] //~ WARN attribute must be of the form
    | ^^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57321 <https://github.com/rust-lang/rust/issues/57321>
+   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
 

src/test/ui/proc-macro/attribute.stderr

@@ -34,13 +34,13 @@ error: attribute must have either one or two arguments
 LL | #[proc_macro_derive(l, attributes(m), n)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: attribute must be of the form `#[proc_macro_derive(TraitName, attributes(name1, name2, ...))]`
+error: attribute must be of the form `#[proc_macro_derive(TraitName, /*opt*/ attributes(name1, name2, ...))]`
   --> $DIR/attribute.rs:8:1
    |
 LL | #[proc_macro_derive]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: attribute must be of the form `#[proc_macro_derive(TraitName, attributes(name1, name2, ...))]`
+error: attribute must be of the form `#[proc_macro_derive(TraitName, /*opt*/ attributes(name1, name2, ...))]`
   --> $DIR/attribute.rs:14:1
    |
 LL | #[proc_macro_derive = "foo"]