Don't spin expanding stmt macros.

If we can't make progress when parsing a macro expansion as a statement
then we should just bail.

This alleviates the symptoms shown in e.g. #37113 but it doesn't fix the
problem that parsing invalid enum bodies (and others) leaves the parser
in a crappy state.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index e84a9208029..6592dff4fb8 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -536,7 +536,9 @@ impl<'a> Parser<'a> {
             }
             ExpansionKind::Stmts => {
                 let mut stmts = SmallVector::zero();
-                while self.token != token::Eof {
+                while self.token != token::Eof &&
+                      // won't make progress on a `}`
+                      self.token != token::CloseDelim(token::Brace) {
                     if let Some(stmt) = self.parse_full_stmt(macro_legacy_warnings)? {
                         stmts.push(stmt);
                     }