On Thu, Jun 29, 2023 at 01:43:07PM -0400, Jason Merrill wrote:
> On 6/24/23 09:24, Nathaniel Shead wrote:
> > On Fri, Jun 23, 2023 at 11:59:51AM -0400, Patrick Palka wrote:
> > > Hi,
> > >
> > > On Sat, 22 Apr 2023, Nathaniel Shead via Gcc-patches wrote:
> > >
> > > > Bootstrapped and tested on x86_64-pc-linux-gnu.
> > > >
> > > > -- 8< --
> > > >
> > > > This patch raises an error early when the decltype(auto) specifier is
> > > > used as a parameter of a function. This prevents any issues with an
> > > > unexpected tree type later on when performing the call.
> > >
> > > Thanks very much for the patch! Some minor comments below.
> > >
> > > >
> > > > PR 103497
> > >
> > > We should include the bug component name when referring to the PR in the
> > > commit message (i.e. PR c++/103497) so that upon pushing the patch the
> > > post-commit hook automatically adds a comment to the PR reffering to the
> > > commit. I could be wrong but AFAIK the hook only performs this when the
> > > component name is included.
> >
> > Thanks for the review! Fixed.
> >
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > > * parser.cc (cp_parser_simple_type_specifier): Add check for
> > > > decltype(auto) as function parameter.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * g++.dg/pr103497.C: New test.
> > > >
> > > > Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> > > > ---
> > > > gcc/cp/parser.cc | 10 ++++++++++
> > > > gcc/testsuite/g++.dg/pr103497.C | 7 +++++++
> > > > 2 files changed, 17 insertions(+)
> > > > create mode 100644 gcc/testsuite/g++.dg/pr103497.C
> > > >
> > > > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> > > > index e5f032f2330..1415e07e152 100644
> > > > --- a/gcc/cp/parser.cc
> > > > +++ b/gcc/cp/parser.cc
> > > > @@ -19884,6 +19884,16 @@ cp_parser_simple_type_specifier (cp_parser*
> > > > parser,
> > > > && cp_lexer_peek_nth_token (parser->lexer, 2)->type !=
> > > > CPP_SCOPE)
> > > > {
> > > > type = saved_checks_value (token->u.tree_check_value);
> > > > + /* Within a function parameter declaration, decltype(auto) is
> > > > always an
> > > > + error. */
> > > > + if (parser->auto_is_implicit_function_template_parm_p
> > > > + && TREE_CODE (type) == TEMPLATE_TYPE_PARM
> > >
> > > We could check is_auto (type) here instead, to avoid any confusion with
> > > checking AUTO_IS_DECLTYPE for a non-auto TEMPLATE_TYPE_PARM.
> > >
> > > > + && AUTO_IS_DECLTYPE (type))
> > > > + {
> > > > + error_at (token->location,
> > > > + "cannot declare a parameter with
> > > > %<decltype(auto)%>");
> > > > + type = error_mark_node;
> > > > + }
> > > > if (decl_specs)
> > > > {
> > > > cp_parser_set_decl_spec_type (decl_specs, type,
> > > > diff --git a/gcc/testsuite/g++.dg/pr103497.C
> > > > b/gcc/testsuite/g++.dg/pr103497.C
> > > > new file mode 100644
> > > > index 00000000000..bcd421c2907
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/g++.dg/pr103497.C
> > > > @@ -0,0 +1,7 @@
> > > > +// { dg-do compile { target c++14 } }
> > > > +
> > > > +void foo(decltype(auto)... args); // { dg-error "parameter with
> > > > .decltype.auto..|no parameter packs" }
> > >
> > > I noticed for
> > >
> > > void foo(decltype(auto) arg);
> > >
> > > we already issue an identical error from grokdeclarator. Perhaps we could
> > > instead extend the error handling there to detect decltype(auto)... as
> > > well,
> > > rather than adding new error handling in cp_parser_simple_type_specifier?
> >
> > Ah thanks, I didn't notice this; this simplifies the change a fair bit.
> > How about this patch instead?
> >
> > Regtested on x86_64-pc-linux-gnu.
> >
> > -- 8< --
> >
> > This patch ensures that checks for usages of 'auto' in function
> > parameters also consider parameter packs, since 'type_uses_auto' does
> > not seem to consider this case.
> >
> > PR c++/103497
> >
> > gcc/cp/ChangeLog:
> >
> > * decl.cc (grokdeclarator): Check for decltype(auto) in
> > parameter pack.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp1y/decltype-auto-103497.C: New test.
> >
> > Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> > ---
> > gcc/cp/decl.cc | 3 +++
> > gcc/testsuite/g++.dg/cpp1y/decltype-auto-103497.C | 8 ++++++++
> > 2 files changed, 11 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto-103497.C
> >
> > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> > index 60f107d50c4..aaf691fce68 100644
> > --- a/gcc/cp/decl.cc
> > +++ b/gcc/cp/decl.cc
> > @@ -14044,6 +14044,9 @@ grokdeclarator (const cp_declarator *declarator,
> > error ("cannot use %<::%> in parameter declaration");
> > tree auto_node = type_uses_auto (type);
> > + if (!auto_node && parameter_pack_p)
> > + auto_node = type_uses_auto (PACK_EXPANSION_PATTERN (type));
>
> Hmm, I wonder if type_uses_auto should look into PACK_EXPANSION_PATTERN
> itself. Would that break anything?
I gave that a try and it seems to work fine.
Regtested on x86_64-pc-linux-gnu.
-- 8< --
This patch ensures 'type_uses_auto' also checks for usages of 'auto' in
parameter packs.
PR c++/103497
gcc/cp/ChangeLog:
* pt.cc (type_uses_auto): Check inside parameter packs.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/decltype-auto-103497.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
---
gcc/cp/pt.cc | 7 ++++++-
gcc/testsuite/g++.dg/cpp1y/decltype-auto-103497.C | 8 ++++++++
2 files changed, 14 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto-103497.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 2345a18becc..2a3ba5ab67d 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -31083,7 +31083,12 @@ type_uses_auto (tree type)
{
if (type == NULL_TREE)
return NULL_TREE;
- else if (flag_concepts_ts)
+
+ /* For parameter packs, check the contents of the pack. */
+ if (PACK_EXPANSION_P (type))
+ type = PACK_EXPANSION_PATTERN (type);
+
+ if (flag_concepts_ts)
{
/* The Concepts TS allows multiple autos in one type-specifier; just
return the first one we find, do_auto_deduction will collect all of
diff --git a/gcc/testsuite/g++.dg/cpp1y/decltype-auto-103497.C
b/gcc/testsuite/g++.dg/cpp1y/decltype-auto-103497.C
new file mode 100644
index 00000000000..cedd661710c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/decltype-auto-103497.C
@@ -0,0 +1,8 @@
+// PR c++/103497
+// { dg-do compile { target c++14 } }
+
+void foo(decltype(auto)... args); // { dg-error "cannot declare a parameter
with .decltype.auto.." }
+
+int main() {
+ foo();
+}
--
2.41.0
