On Tue, Mar 08, 2022 at 02:47:42PM -0500, Jason Merrill wrote:
> On 3/2/22 14:31, Marek Polacek wrote:
> > 104752 points out that
> >
> > template<class T>
> > concept C = true;
> > auto y = C auto(1);
> >
> > is ill-formed as per [dcl.type.auto.deduct]: "For an explicit type
> > conversion,
> > T is the specified type, which shall be auto." which doesn't allow
> > type-constraint auto.
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > PR c++/104752
> >
> > gcc/cp/ChangeLog:
> >
> > * semantics.cc (finish_compound_literal): Disallow auto{x} for
> > is_constrained_auto.
> > * typeck2.cc (build_functional_cast_1): Likewise.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp23/auto-fncast12.C: New test.
> > ---
> > gcc/cp/semantics.cc | 1 +
> > gcc/cp/typeck2.cc | 1 +
> > gcc/testsuite/g++.dg/cpp23/auto-fncast12.C | 8 ++++++++
> > 3 files changed, 10 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-fncast12.C
> >
> > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> > index a2c0eb050e6..5129b12f00f 100644
> > --- a/gcc/cp/semantics.cc
> > +++ b/gcc/cp/semantics.cc
> > @@ -3148,6 +3148,7 @@ finish_compound_literal (tree type, tree
> > compound_literal,
> > /* C++23 auto{x}. */
> > else if (is_auto (type)
> > && !AUTO_IS_DECLTYPE (type)
> > + && !is_constrained_auto (type)
> > && CONSTRUCTOR_NELTS (compound_literal) == 1)
> > {
> > if (cxx_dialect < cxx23)
> > diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
> > index 39d03e4c3c4..c9314bbeb6f 100644
> > --- a/gcc/cp/typeck2.cc
> > +++ b/gcc/cp/typeck2.cc
> > @@ -2305,6 +2305,7 @@ build_functional_cast_1 (location_t loc, tree exp,
> > tree parms,
> > init = parms;
> > /* C++23 auto(x). */
> > else if (!AUTO_IS_DECLTYPE (anode)
> > + && !is_constrained_auto (anode)
> > && list_length (parms) == 1)
> > {
> > init = TREE_VALUE (parms);
>
> We might get a better diagnostic by moving this test inside the block and
> saying that the auto can't be constrained, instead of "invalid use of auto"?
Sure. So like this?
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
104752 points out that
template<class T>
concept C = true;
auto y = C auto(1);
is ill-formed as per [dcl.type.auto.deduct]: "For an explicit type conversion,
T is the specified type, which shall be auto." which doesn't allow
type-constraint auto.
PR c++/104752
gcc/cp/ChangeLog:
* semantics.cc (finish_compound_literal): Disallow auto{x} for
is_constrained_auto.
* typeck2.cc (build_functional_cast_1): Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/cpp23/auto-fncast12.C: New test.
---
gcc/cp/semantics.cc | 8 +++++++-
gcc/cp/typeck2.cc | 8 +++++++-
gcc/testsuite/g++.dg/cpp23/auto-fncast12.C | 8 ++++++++
3 files changed, 22 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-fncast12.C
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 799ce943279..21740064d3d 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -3150,7 +3150,13 @@ finish_compound_literal (tree type, tree
compound_literal,
&& !AUTO_IS_DECLTYPE (type)
&& CONSTRUCTOR_NELTS (compound_literal) == 1)
{
- if (cxx_dialect < cxx23)
+ if (is_constrained_auto (type))
+ {
+ if (complain & tf_error)
+ error ("%<auto{x}%> cannot be constrained");
+ return error_mark_node;
+ }
+ else if (cxx_dialect < cxx23)
pedwarn (input_location, OPT_Wc__23_extensions,
"%<auto{x}%> only available with "
"%<-std=c++2b%> or %<-std=gnu++2b%>");
diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 39d03e4c3c4..a4c825fc34d 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -2308,7 +2308,13 @@ build_functional_cast_1 (location_t loc, tree exp, tree
parms,
&& list_length (parms) == 1)
{
init = TREE_VALUE (parms);
- if (cxx_dialect < cxx23)
+ if (is_constrained_auto (anode))
+ {
+ if (complain & tf_error)
+ error_at (loc, "%<auto(x)%> cannot be constrained");
+ return error_mark_node;
+ }
+ else if (cxx_dialect < cxx23)
pedwarn (loc, OPT_Wc__23_extensions,
"%<auto(x)%> only available with "
"%<-std=c++2b%> or %<-std=gnu++2b%>");
diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast12.C
b/gcc/testsuite/g++.dg/cpp23/auto-fncast12.C
new file mode 100644
index 00000000000..2856c2846fc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast12.C
@@ -0,0 +1,8 @@
+// PR c++/104752
+// { dg-do compile { target c++23 } }
+
+template<class T>
+concept C = true;
+auto x = auto(1); // valid (P0849R8)
+auto y = C auto(1); // { dg-error "cannot be constrained" }
+auto z = C auto{1}; // { dg-error "cannot be constrained" }
base-commit: bded0d549fdfdc1328b2c0189dc5f8593b4cbe42
--
2.35.1
