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, 31 insertions, 4 deletions

diff --git a/gcc/rust/rust-session-manager.cc b/gcc/rust/rust-session-manager.cc
index 6966ccc..d4e3715 100644
--- a/gcc/rust/rust-session-manager.cc
+++ b/gcc/rust/rust-session-manager.cc
@@ -827,9 +827,6 @@ Session::injection (AST::Crate &crate)
 void
 Session::expansion (AST::Crate &crate)
 {
-  /* We need to name resolve macros and imports here */
-  Resolver::EarlyNameResolver ().go (crate);
-
   rust_debug ("started expansion");
 
   /* rustc has a modification to windows PATH temporarily here, which may end
@@ -839,11 +836,41 @@ Session::expansion (AST::Crate &crate)
   // if not, would at least have to configure recursion_limit
   ExpansionCfg cfg;
 
+  auto fixed_point_reached = false;
+  unsigned iterations = 0;
+
   // create extctxt? from parse session, cfg, and resolver?
   /* expand by calling cxtctxt object's monotonic_expander's expand_crate
    * method. */
   MacroExpander expander (crate, cfg, *this);
-  expander.expand_crate ();
+
+  while (!fixed_point_reached && iterations < cfg.recursion_limit)
+    {
+      /* We need to name resolve macros and imports here */
+      Resolver::EarlyNameResolver ().go (crate);
+
+      expander.expand_crate ();
+
+      fixed_point_reached = !expander.has_changed ();
+      expander.reset_changed_state ();
+      iterations++;
+
+      if (saw_errors ())
+	break;
+    }
+
+  if (iterations == cfg.recursion_limit)
+    {
+      auto last_invoc = expander.get_last_invocation ();
+      auto last_def = expander.get_last_definition ();
+
+      rust_assert (last_def && last_invoc);
+
+      RichLocation range (last_invoc->get_locus ());
+      range.add_range (last_def->get_locus ());
+
+      rust_error_at (range, "reached recursion limit");
+    }
 
   // error reporting - check unused macros, get missing fragment specifiers