New attribute parsing infrastructure

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -1,12 +1,25 @@
-mod allow_unstable;
-mod cfg;
-mod confusables;
-mod deprecation;
-mod repr;
-mod stability;
-mod transparency;
+//! You can find more docs on what groups are on [`AttributeParser`] itself.
+//! However, for many types of attributes, implementing [`AttributeParser`] is not necessary.
+//! It allows for a lot of flexibility you might not want.
+//!
+//! Specifically, you might not care about managing the state of your [`AttributeParser`]
+//! state machine yourself. In this case you can choose to implement:
+//!
+//! - [`SingleAttributeParser`]: makes it easy to implement an attribute which should error if it
+//! appears more than once in a list of attributes
+//! - [`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_GROUP_MAPPING`](crate::context::ATTRIBUTE_GROUP_MAPPING) to be parsed.
 
-pub mod util;
+pub(crate) mod allow_unstable;
+pub(crate) mod cfg;
+pub(crate) mod confusables;
+pub(crate) mod deprecation;
+pub(crate) mod repr;
+pub(crate) mod stability;
+pub(crate) mod transparency;
+pub(crate) mod util;
 
 pub use allow_unstable::*;
 pub use cfg::*;

compiler/rustc_attr_parsing/src/lib.rs

@@ -1,8 +1,41 @@
-//! Functions and types dealing with attributes and meta items.
+//! Centralized logic for parsing and attributes.
 //!
-//! FIXME(Centril): For now being, much of the logic is still in `rustc_ast::attr`.
-//! The goal is to move the definition of `MetaItem` and things that don't need to be in `syntax`
-//! to this crate.
+//! Part of a series of crates:
+//! - rustc_attr_data_structures: contains types that the parsers parse into
+//! - rustc_attr_parsing: this crate
+//! - (in the future): rustc_attr_validation
+//!
+//! History: Check out [#131229](https://github.com/rust-lang/rust/issues/131229).
+//! There used to be only one definition of attributes in the compiler: `ast::Attribute`.
+//! These were then parsed or validated or both in places distributed all over the compiler.
+//! This was a mess...
+//!
+//! Attributes are markers on items. Most are actually attribute-like proc-macros, and are expanded
+//! but some remain as the so-called built-in attributes. These are not macros at all, and really
+//! are just markers to guide the compilation process. An example is `#[inline(...)]` which changes
+//! how code for functions is generated. Built-in attributes aren't macros because there's no rust
+//! syntax they could expand to.
+//!
+//! In this crate, syntactical attributes (sequences of tokens that look like
+//! `#[something(something else)]`) are parsed into more semantic attributes, markers on items.
+//! Multiple syntactic attributes might influence a single semantic attribute. For example,
+//! `#[stable(...)]` and `#[unstable()]` cannot occur together, and both semantically define
+//! a "stability" of an item. So, the stability attribute has an
+//! [`AttributeParser`](attributes::AttributeParser) that recognizes both the `#[stable()]`
+//! and `#[unstable()]` syntactic attributes, and at the end produce a single [`AttributeKind::Stability`].
+//!
+//! As a rule of thumb, when a syntactical attribute can be applied more than once, they should be
+//! combined into a single semantic attribute. For example:
+//!
+//! ```
+//! #[repr(C)]
+//! #[repr(packed)]
+//! struct Meow {}
+//! ```
+//!
+//! should result in a single `AttributeKind::Repr` containing a list of repr annotations, in this
+//! case `C` and `packed`. This is equivalent to writing `#[repr(C, packed)]` in a single
+//! syntactical annotation.
 
 // tidy-alphabetical-start
 #![allow(internal_features)]

compiler/rustc_codegen_ssa/src/assert_module_sources.rs

@@ -94,15 +94,15 @@ impl<'tcx> AssertModuleSource<'tcx> {
                 other => {
                     self.tcx
                         .dcx()
-                        .emit_fatal(errors::UnknownReuseKind { span: attr.span, kind: other });
+                        .emit_fatal(errors::UnknownReuseKind { span: attr.span(), kind: other });
                 }
             }
         } else {
             return;
         };
 
         if !self.tcx.sess.opts.unstable_opts.query_dep_graph {
-            self.tcx.dcx().emit_fatal(errors::MissingQueryDepGraph { span: attr.span });
+            self.tcx.dcx().emit_fatal(errors::MissingQueryDepGraph { span: attr.span() });
         }
 
         if !self.check_config(attr) {
@@ -115,7 +115,7 @@ impl<'tcx> AssertModuleSource<'tcx> {
 
         if !user_path.starts_with(&crate_name) {
             self.tcx.dcx().emit_fatal(errors::MalformedCguName {
-                span: attr.span,
+                span: attr.span(),
                 user_path,
                 crate_name,
             });
@@ -145,7 +145,7 @@ impl<'tcx> AssertModuleSource<'tcx> {
             let cgu_names: Vec<&str> =
                 self.available_cgus.items().map(|cgu| cgu.as_str()).into_sorted_stable_ord();
             self.tcx.dcx().emit_err(errors::NoModuleNamed {
-                span: attr.span,
+                span: attr.span(),
                 user_path,
                 cgu_name,
                 cgu_names: cgu_names.join(", "),
@@ -155,7 +155,7 @@ impl<'tcx> AssertModuleSource<'tcx> {
         self.cgu_reuse_tracker.set_expectation(
             cgu_name,
             user_path,
-            attr.span,
+            attr.span(),
             expected_reuse,
             comp_kind,
         );
@@ -175,7 +175,7 @@ impl<'tcx> AssertModuleSource<'tcx> {
             }
         }
 
-        self.tcx.dcx().emit_fatal(errors::NoField { span: attr.span, name });
+        self.tcx.dcx().emit_fatal(errors::NoField { span: attr.span(), name });
     }
 
     /// Scan for a `cfg="foo"` attribute and check whether we have a