Rollup merge of #58654 - estebank:underflow, r=nikomatsakis

Do not underflow after resetting unmatched braces count

Fix #58638.

r? @oli-obk

src/libsyntax/parse/parser.rs

@@ -1184,8 +1184,10 @@ fn expect_gt(&mut self) -> PResult<'a, ()> {
         match ate {
             Some(_) => {
                 // See doc comment for `unmatched_angle_bracket_count`.
-                self.unmatched_angle_bracket_count -= 1;
-                debug!("expect_gt: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+                if self.unmatched_angle_bracket_count > 0 {
+                    self.unmatched_angle_bracket_count -= 1;
+                    debug!("expect_gt: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+                }
 
                 Ok(())
             },
@@ -2248,8 +2250,10 @@ fn parse_qpath(&mut self, style: PathStyle) -> PResult<'a, (QSelf, ast::Path)> {
 
         // See doc comment for `unmatched_angle_bracket_count`.
         self.expect(&token::Gt)?;
-        self.unmatched_angle_bracket_count -= 1;
-        debug!("parse_qpath: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+        if self.unmatched_angle_bracket_count > 0 {
+            self.unmatched_angle_bracket_count -= 1;
+            debug!("parse_qpath: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+        }
 
         self.expect(&token::ModSep)?;