expand: Support helper attributes for built-in derive macros #87027
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
This is needed for #86735 (derive macro
Defaultshould have a helper attributedefault).With this PR we can specify helper attributes for built-in derives using syntax
#[rustc_builtin_macro(MacroName, attributes(attr1, attr2, ...))]which mirrors equivalent syntax for proc macros#[proc_macro_derive(MacroName, attributes(attr1, attr2, ...))].Otherwise expansion infra was already ready for this.
The attribute parsing code is shared between proc macro derives and built-in macros (
fn parse_macro_name_and_helper_attrs).