[gcc r11-9991] c++: template-id with current inst qualifier [PR102300]

[gcc r11-9991] c++: template-id with current inst qualifier [PR102300]

[Jason Merrill]

https://gcc.gnu.org/g:8d2f59c8e26960df81e054c7afd2ef63171bae05

commit r11-9991-g8d2f59c8e26960df81e054c7afd2ef63171bae05
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Jan 18 18:28:22 2022 -0500

    c++: template-id with current inst qualifier [PR102300]
    
    The patch for PR41723 properly changed one place to look into the current
    instantiation; now we need to fix this place as well.
    
    The fix for GCC 12 depends on r12-3643, so this commit also incorporates
    some of those changes.
    
            PR c++/102300
    
    gcc/cp/ChangeLog:
    
            * parser.c (cp_parser_template_name): Use dependent_scope_p.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/parse/no-typename1.C: Remove expected error.
            * g++.dg/template/nested7.C: New test.

Diff:
---
 gcc/cp/parser.c                           | 40 +++++++++++++++++++++----------
 gcc/testsuite/g++.dg/parse/no-typename1.C |  2 +-
 gcc/testsuite/g++.dg/template/nested7.C   | 12 ++++++++++
 3 files changed, 40 insertions(+), 14 deletions(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 365d5989773..b53cc6d360e 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -17728,7 +17728,7 @@ cp_parser_template_name (cp_parser* parser,
 			: parser->context->object_type);
 	  if (scope && TYPE_P (scope)
 	      && (!CLASS_TYPE_P (scope)
-		  || (check_dependency_p && dependent_type_p (scope))))
+		  || (check_dependency_p && dependent_scope_p (scope))))
 	    {
 	      /* We're optimizing away the call to cp_parser_lookup_name, but
 		 we still need to do this.  */
@@ -17739,8 +17739,8 @@ cp_parser_template_name (cp_parser* parser,
     }
 
   /* cp_parser_lookup_name clears OBJECT_TYPE.  */
-  const bool scoped_p = ((parser->scope ? parser->scope
-			  : parser->context->object_type) != NULL_TREE);
+  tree scope = (parser->scope ? parser->scope
+		: parser->context->object_type);
 
   /* Look up the name.  */
   decl = cp_parser_lookup_name (parser, identifier,
@@ -17753,6 +17753,19 @@ cp_parser_template_name (cp_parser* parser,
 
   decl = strip_using_decl (decl);
 
+  /* 13.3 [temp.names] A < is interpreted as the delimiter of a
+    template-argument-list if it follows a name that is not a
+    conversion-function-id and
+    - that follows the keyword template or a ~ after a nested-name-specifier or
+    in a class member access expression, or
+    - for which name lookup finds the injected-class-name of a class template
+    or finds any declaration of a template, or
+    - that is an unqualified name for which name lookup either finds one or
+    more functions or finds nothing, or
+    - that is a terminal name in a using-declarator (9.9), in a declarator-id
+    (9.3.4), or in a type-only context other than a nested-name-specifier
+    (13.8).  */
+
   /* If DECL is a template, then the name was a template-name.  */
   if (TREE_CODE (decl) == TEMPLATE_DECL)
     {
@@ -17772,11 +17785,7 @@ cp_parser_template_name (cp_parser* parser,
     }
   else
     {
-      /* The standard does not explicitly indicate whether a name that
-	 names a set of overloaded declarations, some of which are
-	 templates, is a template-name.  However, such a name should
-	 be a template-name; otherwise, there is no way to form a
-	 template-id for the overloaded templates.  */
+      /* Look through an overload set for any templates.  */
       bool found = false;
 
       for (lkp_iterator iter (MAYBE_BASELINK_FUNCTIONS (decl));
@@ -17784,16 +17793,14 @@ cp_parser_template_name (cp_parser* parser,
 	if (TREE_CODE (*iter) == TEMPLATE_DECL)
 	  found = true;
 
+      /* "an unqualified name for which name lookup either finds one or more
+	 functions or finds nothing".  */
       if (!found
 	  && (cxx_dialect > cxx17)
-	  && !scoped_p
+	  && !scope
 	  && cp_lexer_next_token_is (parser->lexer, CPP_LESS)
 	  && tag_type == none_type)
 	{
-	  /* [temp.names] says "A name is also considered to refer to a template
-	     if it is an unqualified-id followed by a < and name lookup finds
-	     either one or more functions or finds nothing."  */
-
 	  /* The "more functions" case.  Just use the OVERLOAD as normally.
 	     We don't use is_overloaded_fn here to avoid considering
 	     BASELINKs.  */
@@ -17806,6 +17813,13 @@ cp_parser_template_name (cp_parser* parser,
 	    return identifier;
 	}
 
+      /* "that follows the keyword template"..."in a type-only context" */
+      if (!found && scope
+	  && (template_keyword_p || tag_type != none_type)
+	  && TYPE_P (scope) && dependent_type_p (scope)
+	  && cp_parser_nth_token_starts_template_argument_list_p (parser, 1))
+	return identifier;
+
       if (!found)
 	{
 	  /* The name does not name a template.  */
diff --git a/gcc/testsuite/g++.dg/parse/no-typename1.C b/gcc/testsuite/g++.dg/parse/no-typename1.C
index 711c621e26a..f40ea0ec13c 100644
--- a/gcc/testsuite/g++.dg/parse/no-typename1.C
+++ b/gcc/testsuite/g++.dg/parse/no-typename1.C
@@ -6,6 +6,6 @@ template <typename T> struct A
 {
     template <typename U> struct B
     {
-        A<T>::template B<U> foo(); // { dg-error "" "" { target c++17_down } }
+        A<T>::template B<U> foo();
     };
 };
diff --git a/gcc/testsuite/g++.dg/template/nested7.C b/gcc/testsuite/g++.dg/template/nested7.C
new file mode 100644
index 00000000000..3a5930c0f31
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/nested7.C
@@ -0,0 +1,12 @@
+// PR c++/102300
+
+template<typename T>
+struct holder
+{
+  template<typename F> struct fn {};
+
+  struct t1 : fn<T> {};                      // pass
+  struct t2 : holder<T >::fn<T> {};          // fail
+  struct t3 : holder<T >::template fn<T> {}; // fail
+  struct t4 : holder<T*>::template fn<T> {}; // pass
+};