Merge #1750

1750: Implement fixed point macro expansion r=CohenArthur a=CohenArthur

This is a cleanup of #1606's branch, which also contains the code necessary for performing eager macro expansion in builtin macros. 

This commit changes our macro expansion system from an eager and recursive
macro expansion to a fixed-point like system. Instead of, when seeing
a macro invocation, expanding it and all of the macros within it, we
now perform multiple passes of expansion on the entire crate.

This, however, leads to a problem. Rust macros are expanded lazily, but
Rust builtin macros should be expanded eagerly. Due to this, we must
work around the lazy expansion in builtin macros and perform eager
expansion for each pass of the fixed-point, before finally expanding
the builtin when there are no longer any inner macro invocations.

To perform proper macro scoping, the ENR now keeps track of the current
scope (`current_scope` member) and resolves macros accordingly.

This is done through the use of the `scoped` method, which creates a new
scope, runs a specified lambda and then exits the scope. This prevents
pushing/popping errors that we've seen happen already in similar
contexts.

We might think about generalizing it to other classes, providing a
 `Scoped<EntryFn, ExitFn>` class or similar
 
Fixes #1795 

Co-authored-by: Arthur Cohen <arthur.cohen@embecosm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/gcc/rust/parse/rust-parse.h b/gcc/rust/parse/rust-parse.h
index 2f767bb..a4b65c5 100644
--- a/gcc/rust/parse/rust-parse.h
+++ b/gcc/rust/parse/rust-parse.h
@@ -150,6 +150,8 @@ public:
   std::unique_ptr<AST::TokenTree> parse_token_tree ();
   AST::Attribute parse_attribute_body ();
   AST::AttrVec parse_inner_attributes ();
+  std::unique_ptr<AST::MacroInvocation>
+  parse_macro_invocation (AST::AttrVec outer_attrs);
 
 private:
   void skip_after_semicolon ();
@@ -201,8 +203,6 @@ private:
   parse_decl_macro_def (AST::Visibility vis, AST::AttrVec outer_attrs);
   std::unique_ptr<AST::MacroInvocation>
   parse_macro_invocation_semi (AST::AttrVec outer_attrs);
-  std::unique_ptr<AST::MacroInvocation>
-  parse_macro_invocation (AST::AttrVec outer_attrs);
   AST::MacroRule parse_macro_rule ();
   AST::MacroMatcher parse_macro_matcher ();
   std::unique_ptr<AST::MacroMatch> parse_macro_match ();