[gcc r12-6703] c++: input_location and lookahead [PR104025]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:2aa184458a11a7ec8c1b451b8eeff458a24632bb

commit r12-6703-g2aa184458a11a7ec8c1b451b8eeff458a24632bb
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jan 17 17:16:38 2022 -0500

    c++: input_location and lookahead [PR104025]
    
    Debug information was getting confused because input_location was different
    depending on whether we had looked ahead to see if the next tokens look like
    a template argument list.
    
    I tried resetting input_location in cp_lexer_rollback_tokens itself, but
    that caused regressions, so let's just do it here for now.
    
            PR c++/104025
    
    gcc/cp/ChangeLog:
    
            * parser.cc (saved_token_sentinel::rollback): Call
            cp_lexer_set_source_position.
            (~saved_token_sentinel): Call rollback.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/pr104025.C: New test.
    
    Co-authored-by: Jakub Jelinek  <jakub@redhat.com>

Diff:
---
 gcc/cp/parser.cc                     |  3 ++-
 gcc/testsuite/g++.dg/warn/pr104025.C | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index b262b765a9a..60d9f7bb723 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -1308,6 +1308,7 @@ struct saved_token_sentinel
   void rollback ()
   {
     cp_lexer_rollback_tokens (lexer);
+    cp_lexer_set_source_position (lexer);
     mode = STS_DONOTHING;
   }
   ~saved_token_sentinel ()
@@ -1315,7 +1316,7 @@ struct saved_token_sentinel
     if (mode == STS_COMMIT)
       cp_lexer_commit_tokens (lexer);
     else if (mode == STS_ROLLBACK)
-      cp_lexer_rollback_tokens (lexer);
+      rollback ();
 
     gcc_assert (lexer->saved_tokens.length () == len);
   }
diff --git a/gcc/testsuite/g++.dg/warn/pr104025.C b/gcc/testsuite/g++.dg/warn/pr104025.C
new file mode 100644
index 00000000000..9457c8ef52c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/pr104025.C
@@ -0,0 +1,20 @@
+// PR c++/104025
+// { dg-do compile }
+// { dg-options "-Wmissing-template-keyword -fcompare-debug" }
+
+void bar (int);
+
+struct S { int i; };
+
+template <class C>
+struct T
+{
+  int m;
+  C c;
+  void foo ()
+  {
+    bar (c.i < m);
+  }
+};
+
+template void T<S>::foo ();