On Mon, Sep 30, 2024 at 10:53:04AM -0400, Jason Merrill wrote:
> On 9/27/24 5:30 PM, Marek Polacek wrote:
> > On Fri, Sep 27, 2024 at 04:57:58PM -0400, Jason Merrill wrote:
> > > On 9/18/24 5:06 PM, Marek Polacek wrote:
> > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > > >
> > > > -- >8 --
> > > > 1) We're hitting the assert in cp_parser_placeholder_type_specifier.
> > > > It says that if it turns out to be false, we should do error() instead.
> > > > Do so, then.
> > > >
> > > > 2) lambda-targ8.C should compile fine, though. The problem was that
> > > > local_variables_forbidden_p wasn't cleared when we're about to parse
> > > > the optional template-parameter-list for a lambda in a default argument.
> > > >
> > > > PR c++/109859
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > > * parser.cc (cp_parser_lambda_declarator_opt): Temporarily clear
> > > > local_variables_forbidden_p.
> > > > (cp_parser_placeholder_type_specifier): Turn an assert into an
> > > > error.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * g++.dg/cpp2a/concepts-defarg3.C: New test.
> > > > * g++.dg/cpp2a/lambda-targ8.C: New test.
> > > > ---
> > > > gcc/cp/parser.cc | 9 +++++++--
> > > > gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C | 8 ++++++++
> > > > gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C | 10 ++++++++++
> > > > 3 files changed, 25 insertions(+), 2 deletions(-)
> > > > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C
> > > > create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C
> > > >
> > > > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> > > > index 4dd9474cf60..bdc4fef243a 100644
> > > > --- a/gcc/cp/parser.cc
> > > > +++ b/gcc/cp/parser.cc
> > > > @@ -11891,6 +11891,11 @@ cp_parser_lambda_declarator_opt (cp_parser*
> > > > parser, tree lambda_expr)
> > > > "lambda templates are only available with "
> > > > "%<-std=c++20%> or %<-std=gnu++20%>");
> > > > + /* Even though the whole lambda may be a default argument, its
> > > > + template-parameter-list is a context where it's OK to create
> > > > + new parameters. */
> > > > + auto lvf = make_temp_override
> > > > (parser->local_variables_forbidden_p, 0u);
> > > > +
> > > > cp_lexer_consume_token (parser->lexer);
> > > > template_param_list = cp_parser_template_parameter_list
> > > > (parser);
> > > > @@ -20978,8 +20983,8 @@ cp_parser_placeholder_type_specifier (cp_parser
> > > > *parser, location_t loc,
> > > > /* In a default argument we may not be creating new
> > > > parameters. */
> > > > if (parser->local_variables_forbidden_p & LOCAL_VARS_FORBIDDEN)
> > > > {
> > > > - /* If this assert turns out to be false, do error() instead.
> > > > */
> > > > - gcc_assert (tentative);
> > > > + if (!tentative)
> > > > + error_at (loc, "local variables may not appear in this
> > > > context");
> > >
> > > There's no local variable in the new testcase, the error should talk
> > > about a
> > > concept-name.
> >
> > Ah sure. So like this?
> >
> > Tested dg.exp.
> >
> > -- >8 --
> > 1) We're hitting the assert in cp_parser_placeholder_type_specifier.
> > It says that if it turns out to be false, we should do error() instead.
> > Do so, then.
> >
> > 2) lambda-targ8.C should compile fine, though. The problem was that
> > local_variables_forbidden_p wasn't cleared when we're about to parse
> > the optional template-parameter-list for a lambda in a default argument.
> >
> > PR c++/109859
> >
> > gcc/cp/ChangeLog:
> >
> > * parser.cc (cp_parser_lambda_declarator_opt): Temporarily clear
> > local_variables_forbidden_p.
> > (cp_parser_placeholder_type_specifier): Turn an assert into an error.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp2a/concepts-defarg3.C: New test.
> > * g++.dg/cpp2a/lambda-targ8.C: New test.
> > ---
> > gcc/cp/parser.cc | 9 +++++++--
> > gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C | 8 ++++++++
> > gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C | 10 ++++++++++
> > 3 files changed, 25 insertions(+), 2 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C
> >
> > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> > index f50534f5f39..a92e6a29ba6 100644
> > --- a/gcc/cp/parser.cc
> > +++ b/gcc/cp/parser.cc
> > @@ -11891,6 +11891,11 @@ cp_parser_lambda_declarator_opt (cp_parser*
> > parser, tree lambda_expr)
> > "lambda templates are only available with "
> > "%<-std=c++20%> or %<-std=gnu++20%>");
> > + /* Even though the whole lambda may be a default argument, its
> > + template-parameter-list is a context where it's OK to create
> > + new parameters. */
> > + auto lvf = make_temp_override (parser->local_variables_forbidden_p,
> > 0u);
> > +
> > cp_lexer_consume_token (parser->lexer);
> > template_param_list = cp_parser_template_parameter_list (parser);
> > @@ -20989,8 +20994,8 @@ cp_parser_placeholder_type_specifier (cp_parser
> > *parser, location_t loc,
> > /* In a default argument we may not be creating new parameters. */
> > if (parser->local_variables_forbidden_p & LOCAL_VARS_FORBIDDEN)
> > {
> > - /* If this assert turns out to be false, do error() instead. */
> > - gcc_assert (tentative);
> > + if (!tentative)
> > + error_at (loc, "concept-name may not appear in this context");
>
> Hmm, actually I expect it can appear in a concept-id.
Aha. I just followed the commentary.
> What if we fall
> through to the next case instead of erroring/returning at this point?
Then for concepts-defarg3.C we emit:
concepts-defarg3.C:7:19: error: expected 'auto' or 'decltype(auto)' after 'C'
7 | template <class = C> // { dg-error "may not appear in this context" }
| ^
concepts-defarg3.C:7:19: error: invalid use of ‘auto’ in default template
argument
The first error is fine, the second...not so much. We created the
auto at the end of cp_parser_placeholder_type_specifier in
make_constrained_auto. I could fix it by adding a flag and returning early
but maybe it can stay as-is. The fall through after "expected auto" is
deliberate...
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
1) We're hitting the assert in cp_parser_placeholder_type_specifier.
Rather than turning that assert into an error, we can fall through
to the next block to get an error.
2) lambda-targ8.C should compile fine, though. The problem was that
local_variables_forbidden_p wasn't cleared when we're about to parse
the optional template-parameter-list for a lambda in a default argument.
PR c++/109859
gcc/cp/ChangeLog:
* parser.cc (cp_parser_lambda_declarator_opt): Temporarily clear
local_variables_forbidden_p.
(cp_parser_placeholder_type_specifier): Remove an assert; fall
through to the next condition instead.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-defarg3.C: New test.
* g++.dg/cpp2a/lambda-targ8.C: New test.
---
gcc/cp/parser.cc | 20 +++++++++----------
gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C | 8 ++++++++
gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C | 10 ++++++++++
3 files changed, 27 insertions(+), 11 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index f50534f5f39..54c59363da1 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -11891,6 +11891,11 @@ cp_parser_lambda_declarator_opt (cp_parser* parser,
tree lambda_expr)
"lambda templates are only available with "
"%<-std=c++20%> or %<-std=gnu++20%>");
+ /* Even though the whole lambda may be a default argument, its
+ template-parameter-list is a context where it's OK to create
+ new parameters. */
+ auto lvf = make_temp_override (parser->local_variables_forbidden_p, 0u);
+
cp_lexer_consume_token (parser->lexer);
template_param_list = cp_parser_template_parameter_list (parser);
@@ -20984,17 +20989,10 @@ cp_parser_placeholder_type_specifier (cp_parser
*parser, location_t loc,
/* In a template parameter list, a type-parameter can be introduced
by type-constraints alone. */
- if (processing_template_parmlist && !placeholder)
- {
- /* In a default argument we may not be creating new parameters. */
- if (parser->local_variables_forbidden_p & LOCAL_VARS_FORBIDDEN)
- {
- /* If this assert turns out to be false, do error() instead. */
- gcc_assert (tentative);
- return error_mark_node;
- }
- return build_constrained_parameter (con, proto, args);
- }
+ if (processing_template_parmlist
+ && !placeholder
+ && (parser->local_variables_forbidden_p & LOCAL_VARS_FORBIDDEN) == 0)
+ return build_constrained_parameter (con, proto, args);
/* Diagnose issues placeholder issues. */
if (!parser->in_result_type_constraint_p && !placeholder)
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C
new file mode 100644
index 00000000000..aaf3edf77e6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg3.C
@@ -0,0 +1,8 @@
+// PR c++/109859
+// { dg-do compile { target c++20 } }
+
+template<class>
+concept C = true;
+
+template <class = C> // { dg-error "expected|invalid" }
+int f();
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C
b/gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C
new file mode 100644
index 00000000000..3685b0ef880
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-targ8.C
@@ -0,0 +1,10 @@
+// PR c++/109859
+// { dg-do compile { target c++20 } }
+
+template<typename>
+concept A = true;
+
+template<auto = []<A a> {}>
+int x;
+
+void g() { (void) x<>; }
base-commit: 9c14f9a9c19957d9a45a7df97701bad475c80eea
--
2.46.1
