Improve some attribute docs and rename groups

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -12,7 +12,7 @@
 //! - [`CombineAttributeParser`]: makes it easy to implement an attribute which should combine the
 //! contents of attributes, if an attribute appear multiple times in a list
 //!
-//! Attributes should be added to [`ATTRIBUTE_MAPPING`](crate::context::ATTRIBUTE_MAPPING) to be parsed.
+//! Attributes should be added to [`ATTRIBUTE_PARSERS`](crate::context::ATTRIBUTE_PARSERS) to be parsed.
 
 use std::marker::PhantomData;
 
@@ -51,6 +51,9 @@ type AcceptMapping<T> = &'static [(&'static [Symbol], AcceptFn<T>)];
 /// whether it has seen the attribute it has been looking for.
 ///
 /// The state machine is automatically reset to parse attributes on the next item.
+///
+/// For a simpler attribute parsing interface, consider using [`SingleAttributeParser`]
+/// or [`CombineAttributeParser`] instead.
 pub(crate) trait AttributeParser: Default + 'static {
     /// The symbols for the attributes that this parser is interested in.
     ///
@@ -59,6 +62,12 @@ pub(crate) trait AttributeParser: Default + 'static {
 
     /// The parser has gotten a chance to accept the attributes on an item,
     /// here it can produce an attribute.
+    ///
+    /// All finalize methods of all parsers are unconditionally called.
+    /// This means you can't unconditionally return `Some` here,
+    /// that'd be equivalent to unconditionally applying an attribute to
+    /// every single syntax item that could have attributes applied to it.
+    /// Your accept mappings should determine whether this returns something.
     fn finalize(self, cx: &FinalizeContext<'_>) -> Option<AttributeKind>;
 }
 

compiler/rustc_attr_parsing/src/context.rs

@@ -22,7 +22,7 @@ use crate::attributes::transparency::TransparencyParser;
 use crate::attributes::{AttributeParser as _, Combine, Single};
 use crate::parser::{ArgParser, MetaItemParser};
 
-macro_rules! attribute_groups {
+macro_rules! attribute_parsers {
     (
         pub(crate) static $name: ident = [$($names: ty),* $(,)?];
     ) => {
@@ -63,8 +63,8 @@ macro_rules! attribute_groups {
     };
 }
 
-attribute_groups!(
-    pub(crate) static ATTRIBUTE_MAPPING = [
+attribute_parsers!(
+    pub(crate) static ATTRIBUTE_PARSERS = [
         // tidy-alphabetical-start
         BodyStabilityParser,
         ConfusablesParser,
@@ -90,7 +90,7 @@ attribute_groups!(
 ///
 /// Gives [`AttributeParser`]s enough information to create errors, for example.
 pub(crate) struct AcceptContext<'a> {
-    pub(crate) group_cx: &'a FinalizeContext<'a>,
+    pub(crate) finalize_cx: &'a FinalizeContext<'a>,
     /// The span of the attribute currently being parsed
     pub(crate) attr_span: Span,
 }
@@ -109,7 +109,7 @@ impl<'a> Deref for AcceptContext<'a> {
     type Target = FinalizeContext<'a>;
 
     fn deref(&self) -> &Self::Target {
-        &self.group_cx
+        &self.finalize_cx
     }
 }
 
@@ -219,7 +219,7 @@ impl<'sess> AttributeParser<'sess> {
     ) -> Vec<Attribute> {
         let mut attributes = Vec::new();
 
-        let group_cx = FinalizeContext { cx: self, target_span };
+        let finalize_cx = FinalizeContext { cx: self, target_span };
 
         for attr in attrs {
             // If we're only looking for a single attribute, skip all the ones we don't care about.
@@ -268,9 +268,11 @@ impl<'sess> AttributeParser<'sess> {
                     let args = parser.args();
                     let parts = path.segments().map(|i| i.name).collect::<Vec<_>>();
 
-                    if let Some(accept) = ATTRIBUTE_MAPPING.0.get(parts.as_slice()) {
-                        let cx =
-                            AcceptContext { group_cx: &group_cx, attr_span: lower_span(attr.span) };
+                    if let Some(accept) = ATTRIBUTE_PARSERS.0.get(parts.as_slice()) {
+                        let cx = AcceptContext {
+                            finalize_cx: &finalize_cx,
+                            attr_span: lower_span(attr.span),
+                        };
 
                         accept(&cx, &args)
                     } else {
@@ -302,8 +304,8 @@ impl<'sess> AttributeParser<'sess> {
         }
 
         let mut parsed_attributes = Vec::new();
-        for f in &ATTRIBUTE_MAPPING.1 {
-            if let Some(attr) = f(&group_cx) {
+        for f in &ATTRIBUTE_PARSERS.1 {
+            if let Some(attr) = f(&finalize_cx) {
                 parsed_attributes.push(Attribute::Parsed(attr));
             }
         }