https://gcc.gnu.org/g:2ca183c113effe2d334b2227f4fdfa5666db8874
commit r16-2146-g2ca183c113effe2d334b2227f4fdfa5666db8874
Author: Marek Polacek <pola...@redhat.com>
Date: Tue Jul 8 14:36:37 2025 -0400
c++: optional template after :: causing error [PR119838]
Found while working on Reflection where we currently reject:
constexpr auto r = ^^::template C<int>::type;
which should work, because "::template C<int>::" should match the
nested-name-specifier template(opt) simple-template-id ::
production where the template is optional. This bug is not limited
to Reflection as demonstrated by the attached test case, so I'm
submitting it separately.
The check_template_keyword_in_nested_name_spec call should ensure that
we're dealing with a template-id if we've seen "template".
PR c++/119838
gcc/cp/ChangeLog:
* parser.cc (cp_parser_nested_name_specifier_opt): New global_p
parameter. Look for "template" when global_p is true.
(cp_parser_simple_type_specifier): Pass global_p to
cp_parser_nested_name_specifier_opt.
gcc/testsuite/ChangeLog:
* g++.dg/parse/template32.C: New test.
Reviewed-by: Jason Merrill <ja...@redhat.com>
Diff:
---
gcc/cp/parser.cc | 35 ++++++++++++++++++++++-----------
gcc/testsuite/g++.dg/parse/template32.C | 13 ++++++++++++
2 files changed, 36 insertions(+), 12 deletions(-)
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 8148495f9887..968c0f50d162 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -2519,7 +2519,7 @@ static cp_expr cp_parser_id_expression
static cp_expr cp_parser_unqualified_id
(cp_parser *, bool, bool, bool, bool);
static tree cp_parser_nested_name_specifier_opt
- (cp_parser *, bool, bool, bool, bool, bool = false);
+ (cp_parser *, bool, bool, bool, bool, bool = false, bool = false);
static tree cp_parser_nested_name_specifier
(cp_parser *, bool, bool, bool, bool);
static tree cp_parser_qualifying_entity
@@ -7242,18 +7242,22 @@ check_template_keyword_in_nested_name_spec (tree name)
nested-name-specifier template [opt] simple-template-id ::
PARSER->SCOPE should be set appropriately before this function is
- called. TYPENAME_KEYWORD_P is TRUE if the `typename' keyword is in
- effect. TYPE_P is TRUE if we non-type bindings should be ignored
- in name lookups.
+ called. TYPENAME_KEYWORD_P is true if the `typename' keyword is in
+ effect. TYPE_P is true if we non-type bindings should be ignored
+ in name lookups. TEMPLATE_KEYWORD_P is true if the `template' keyword
+ was seen. GLOBAL_P is true if `::' has already been parsed.
+ TODO: This function doesn't handle the C++14 change to make `::'
+ a nested-name-specifier by itself. If it did, GLOBAL_P could probably
+ go.
Sets PARSER->SCOPE to the class (TYPE) or namespace
(NAMESPACE_DECL) specified by the nested-name-specifier, or leaves
it unchanged if there is no nested-name-specifier. Returns the new
scope iff there is a nested-name-specifier, or NULL_TREE otherwise.
- If CHECK_DEPENDENCY_P is FALSE, names are looked up in dependent scopes.
+ If CHECK_DEPENDENCY_P is false, names are looked up in dependent scopes.
- If IS_DECLARATION is TRUE, the nested-name-specifier is known to be
+ If IS_DECLARATION is true, the nested-name-specifier is known to be
part of a declaration and/or decl-specifier. */
static tree
@@ -7262,7 +7266,8 @@ cp_parser_nested_name_specifier_opt (cp_parser *parser,
bool check_dependency_p,
bool type_p,
bool is_declaration,
- bool template_keyword_p /* = false */)
+ bool template_keyword_p /* = false */,
+ bool global_p /* = false */)
{
bool success = false;
cp_token_position start = 0;
@@ -7310,8 +7315,9 @@ cp_parser_nested_name_specifier_opt (cp_parser *parser,
/* Spot cases that cannot be the beginning of a
nested-name-specifier. On the second and subsequent times
- through the loop, we look for the `template' keyword. */
- if (success && token->keyword == RID_TEMPLATE)
+ (or the first, if '::' has already been parsed) through the
+ loop, we look for the `template' keyword. */
+ if ((success || global_p) && token->keyword == RID_TEMPLATE)
;
/* A template-id can start a nested-name-specifier. */
else if (token->type == CPP_TEMPLATE_ID)
@@ -7359,8 +7365,11 @@ cp_parser_nested_name_specifier_opt (cp_parser *parser,
cp_parser_parse_tentatively (parser);
/* Look for the optional `template' keyword, if this isn't the
- first time through the loop. */
- if (success)
+ first time through the loop, or if we've already parsed '::';
+ this is then the
+ nested-name-specifier template [opt] simple-template-id ::
+ production. */
+ if (success || global_p)
{
template_keyword_p = cp_parser_optional_template_keyword (parser);
/* DR1710: "In a qualified-id used as the name in
@@ -21167,7 +21176,9 @@ cp_parser_simple_type_specifier (cp_parser* parser,
/*typename_keyword_p=*/false,
/*check_dependency_p=*/true,
/*type_p=*/false,
- /*is_declaration=*/false)
+ /*is_declaration=*/false,
+ /*template_keyword_p=*/false,
+ global_p)
!= NULL_TREE);
/* If we have seen a nested-name-specifier, and the next token
is `template', then we are using the template-id production. */
diff --git a/gcc/testsuite/g++.dg/parse/template32.C
b/gcc/testsuite/g++.dg/parse/template32.C
new file mode 100644
index 000000000000..b090f4074e38
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/template32.C
@@ -0,0 +1,13 @@
+// PR c++/119838
+// { dg-do compile { target c++11 } }
+
+template<typename T>
+struct S { using U = T; static const int x = 0; };
+void
+g ()
+{
+ ::S<int>::U a;
+ ::template S<int>::U b;
+ auto c = ::S<int>::x;
+ auto d = ::template S<int>::x;
+}
