[PATCH] c++: Fox template-introduction tentative parsing in class bodies clear colon_corrects_to_scope_p [PR105061]

[Jakub Jelinek via Gcc-patches]

Hi!

The concepts support (in particular template introductions from concepts TS)
broke the following testcase, valid unnamed bitfields with dependent
types (or even just typedefs) were diagnosed as typos (: instead of correct
::) in template introduction during their tentative parsing.
The following patch fixes that by not doing this : to :: correction when
member_p is true.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk and
release branches (so far also bootstrapped/regtested on the above targets
on 11 branch)?

2022-03-29  Jakub Jelinek  <ja...@redhat.com>

        PR c++/105061
        * parser.cc (cp_parser_template_introduction): If member_p, temporarily
        clear parser->colon_corrects_to_scope_p around tentative parsing of
        nested name specifier.

        * g++.dg/concepts/pr105061.C: New test.

--- gcc/cp/parser.cc.jj 2022-03-26 08:11:50.030217910 +0100
+++ gcc/cp/parser.cc    2022-03-28 17:30:41.488053848 +0200
@@ -31417,9 +31417,15 @@ cp_parser_template_introduction (cp_pars
   tree saved_scope = parser->scope;
   tree saved_object_scope = parser->object_scope;
   tree saved_qualifying_scope = parser->qualifying_scope;
+  bool saved_colon_corrects_to_scope_p = parser->colon_corrects_to_scope_p;
 
   cp_token *start_token = cp_lexer_peek_token (parser->lexer);
 
+  /* In classes don't parse valid unnamed bitfields as invalid
+     template introductions.  */
+  if (member_p)
+    parser->colon_corrects_to_scope_p = false;
+
   /* Look for the optional `::' operator.  */
   cp_parser_global_scope_opt (parser,
                              /*current_scope_valid_p=*/false);
@@ -31440,6 +31446,7 @@ cp_parser_template_introduction (cp_pars
   parser->scope = saved_scope;
   parser->object_scope = saved_object_scope;
   parser->qualifying_scope = saved_qualifying_scope;
+  parser->colon_corrects_to_scope_p = saved_colon_corrects_to_scope_p;
 
   if (concept_name == error_mark_node
       || (seen_error () && !concept_definition_p (tmpl_decl)))
--- gcc/testsuite/g++.dg/concepts/pr105061.C.jj 2022-03-28 17:34:02.051207207 
+0200
+++ gcc/testsuite/g++.dg/concepts/pr105061.C    2022-03-28 17:33:14.502882074 
+0200
@@ -0,0 +1,13 @@
+// PR c++/105061
+
+template <typename T, int U, int V>
+struct A { T : V, u : U; };
+template <int U, int V>
+struct B { unsigned : V, u : U; };
+typedef unsigned uns;
+template <int U, int V>
+struct C { uns : V, u : U; };
+
+A<unsigned int, 4, 5> a = { 13 };
+B<5, 6> b = { 26 };
+C<8, 9> c = { 42 };

        Jakub