Change span field accesses to method calls

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::*;