On Fri, Mar 06, 2026 at 10:15:37AM +0000, Boris Staletic wrote:
> On Thursday, March 5th, 2026 at 11:31 PM, Marek Polacek <[email protected]>
> wrote:
>
> > On Thu, Mar 05, 2026 at 06:18:13PM -0500, Jason Merrill wrote:
> > > On 3/5/26 5:35 PM, Marek Polacek wrote:
> > > > On Thu, Mar 05, 2026 at 05:13:32PM -0500, Jason Merrill wrote:
> > > > > On 3/5/26 2:07 PM, Marek Polacek wrote:
> > > > > > On Wed, Mar 04, 2026 at 07:13:33PM +0000, Boris Staletic wrote:
> > > > > > > Bootstrapped and tested on x86_64-pc-linux-gnu.
> > > > > > > I have only ran g++.dg/reflect/* tests.
> > > > > > > If needed/wanted, I can run the entire `make check`, though
> > > > > > > that will take me the rest of the night.
> > > > > > > -- >8 --
> > > > > > > With an annotation like [[=func]] gcc ends up calling
> > > > > > > handle_annotation_attribute with TREE_VALUE (args) being a
> > > > > > > VIEW_CONVERT_EXPR, whose type is a FUNCTION_TYPE.
> > > > > > > That kind of annotation value should be decayed before checking
> > > > > > > if the type is structural.
> > > > > > >
> > > > > > > Signed-off-by: Boris Staletic <[email protected]>
> > > > > > >
> > > > > > > PR c++/124177
> > > > > > >
> > > > > > > gcc/cp/ChangeLog:
> > > > > > >
> > > > > > > * tree.cc (handle_annotation_attribute): Decay annotation
> > > > > > > values.
> > > > > >
> > > > > > This can fit on one line (80 is the limit).
> > > > >
> > > > > I prefer to wrap at 76 in commit messages because git log adds 4
> > > > > spaces at
> > > > > the beginning.
> > > >
> > > > Fair.
> > > >
> > > > > > > gcc/testsuite/ChangeLog:
> > > > > > >
> > > > > > > * g++.dg/reflect/annotations11.C: New test.
> > > > > > > ---
> > > > > > > gcc/cp/tree.cc | 1 +
> > > > > > > gcc/testsuite/g++.dg/reflect/annotations11.C | 17
> > > > > > > +++++++++++++++++
> > > > > > > 2 files changed, 18 insertions(+)
> > > > > > > create mode 100644 gcc/testsuite/g++.dg/reflect/annotations11.C
> > > > > > >
> > > > > > > diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> > > > > > > index 20288ed04e..5c7df0a1d9 100644
> > > > > > > --- a/gcc/cp/tree.cc
> > > > > > > +++ b/gcc/cp/tree.cc
> > > > > > > @@ -5912,6 +5912,7 @@ handle_annotation_attribute (tree *node,
> > > > > > > tree ARG_UNUSED (name),
> > > > > > > *no_add_attrs = true;
> > > > > > > return NULL_TREE;
> > > > > > > }
> > > > > > > + TREE_VALUE (args) = decay_conversion (TREE_VALUE (args),
> > > > > > > tf_warning_or_error);
> > > > > >
> > > > > > I'm not sure if it's reasonable to call decay_conversion on
> > > > > > something
> > > > > > type-dependent, so perhaps this should be moved inside of the
> > > > > > following
> > > > > > block.
> > > > >
> > > > > Good point.
> > > > >
> > > > > > But annotations are treated as late attributes so I'm not sure
> > > > > > how we'd get here with anything type-dependent, and I couldn't
> > > > > > construct
> > > > > > such a test. Maybe the !t_d_e_p check could be dropped?
> > > > >
> > > > > Or turned into an assert.
> > > >
> > > > Sounds good. I can do it later.
> > > >
> > > > > > We're supposed to treat the expression as reflect_constant(arg) but
> > > > > > doing the whole convert_reflect_constant_arg thing here seems
> > > > > > unpleasant.
> > > > >
> > > > > Hmm, why unpleasant? It seems straightforward and might be needed to
> > > > > get
> > > > > some messy cases right.
> > > >
> > > > I think it might need
> > > >
> > > > /* Figure out the type for reflect_constant. */
> > > > type = TREE_TYPE (convert_from_reference (r));
> > > > type = type_decays_to (type);
> > > > type = cv_unqualified (type);
> > >
> > > convert_for_reference shouldn't be needed here.
> >
> > Without it we don't compile this:
> >
> > constexpr int a = 3;
> > constexpr const int &ref = a;
> > static_assert (type_of (constant_of (^^ref)) == ^^int);
> >
> > due to
> >
> > error: 'const int&' must be a cv-unqualified structural type that is not
> > a reference type
> >
> > > type_decays_to/cv_unqualified to correspond to the [type.deduct.call]
> > > changes in maybe_adjust_types_for_deduction, sure. And then we wouldn't
> > > need the decay_conversion after all.
> > >
> > > > for the type, then check !structural_type_p and copy constructibility,
> > > > then call convert_reflect_constant_arg, and check for error_mark_node.
> > >
> > > Agreed.
> > >
> > > > But I think convert_reflect_constant_arg isn't entirely correct yet
> > > > (FIXME in reflect_constant6.C).
> > >
> > > Perhaps, but that doesn't seem like an argument against using it here.
> >
> > I agree, it will probably work for all our annotation uses.
> >
> >
> > Boris, let me know if you want me to take this over.
>
> I did implement the proposed changes, but it resulted in three regressions.
> Here's the commit with the changes (I was lazy and didn't adjust the commit
> message):
> https://codeberg.org/bstaletic/gcc/commit/8bacdc8ac390df094c9cec74ca6f717168eb7213
> I pushed my updated commit to my fork[0].
>
> Make sure to ignore whitespace when looking at the diff, due to indentation
> changes.
>
> The regressions are:
> 1. For `[[=(throw 2, 0)]]`, the annotation evaluation no longer throws. Test
> at: [1]
> 2. One test[2] is now hitting an assert[3]
> 3. Annotations whose value is a user defined type no longer have a proper
> source location.
> 3.1. Existing test case: [4]
>
> For the throw expression, if I change it to `[[=(throw 2)]]`, then I just get
> "annotation does not have a structural type", but there's no uncaught
> exception error.
>
> Regarding source location, both DECL_ARTIFICIAL (expr) and DECL_IGNORED_P
> (expr),
> so we end up returning early from maybe_wrap_with_location here: [5]
> I have not checked whether that is also the case for these test cases: [6][7]
>
> Then, for the assert, the full trace is:
>
> ```
> 0x2a9417f internal_error(char const*, ...)
> ../../gcc/diagnostic-global-context.cc:787
> 0xafd767 fancy_abort(char const*, int, char const*)
> ../../gcc/diagnostics/context.cc:1813
> 0x830050 create_template_parm_object
> ../../gcc/cp/pt.cc:7504
> 0x830050 convert_nontype_argument
> ../../gcc/cp/pt.cc:8042
> 0xd8dc5c convert_reflect_constant_arg(tree_node*, tree_node*)
> ../../gcc/cp/pt.cc:33576
> 0xe38a34 handle_annotation_attribute
> ../../gcc/cp/tree.cc:5947
> 0xbf691a xref_basetypes(tree_node*, tree_node*)
> ../../gcc/cp/decl.cc:18611
> 0xdc5225 instantiate_class_template(tree_node*)
> ../../gcc/cp/pt.cc:12919
> 0xe3eb03 complete_type(tree_node*)
> ../../gcc/cp/typeck.cc:138
> 0xe3eca4 complete_type(tree_node*)
> ../../gcc/cp/typeck.cc:164
> 0xe3eca4 complete_type_or_maybe_complain(tree_node*, tree_node*, int)
> ../../gcc/cp/typeck.cc:151
> 0xde3a92 eval_bases_of
> ../../gcc/cp/reflect.cc:6845
> 0xde3a92 process_metafunction(constexpr_ctx const*, tree_node*, tree_node*,
> bool*, bool*, tree_node**)
> ../../gcc/cp/reflect.cc:7661
> 0xb5c204 cxx_eval_call_expression
> ../../gcc/cp/constexpr.cc:4014
> 0xb5fcfd cxx_eval_constant_expression(constexpr_ctx const*, tree_node*,
> value_cat, bool*, bool*, tree_node**)
> ../../gcc/cp/constexpr.cc:9352
> 0xb62b7c cxx_eval_constant_expression(constexpr_ctx const*, tree_node*,
> value_cat, bool*, bool*, tree_node**)
> ../../gcc/cp/constexpr.cc:9489
> 0xb60d15 cxx_eval_constant_expression(constexpr_ctx const*, tree_node*,
> value_cat, bool*, bool*, tree_node**)
> ../../gcc/cp/constexpr.cc:9770
> 0xb5c772 cxx_bind_parameters_in_call
> ../../gcc/cp/constexpr.cc:2913
> 0xb5c772 cxx_eval_call_expression
> ../../gcc/cp/constexpr.cc:4234
> 0xb5fcfd cxx_eval_constant_expression(constexpr_ctx const*, tree_node*,
> value_cat, bool*, bool*, tree_node**)
> ../../gcc/cp/constexpr.cc:9352
> ```
>
>
>
> [0]:
> https://codeberg.org/bstaletic/gcc/commit/8bacdc8ac390df094c9cec74ca6f717168eb7213
> [1]:
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.dg/reflect/annotations2.C;h=77b581165f14ddffbba51275caa0b5810d680075;hb=HEAD#l33
> [2]:
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.dg/reflect/annotations3.C;h=1f80d7a1851298bc931b89db163711c5a29a3ab9;hb=HEAD#l147
> [3]:
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/cp/pt.cc;h=ddf492b34354ec1aa398cd945162378a09ac570e;hb=b95955b8854ae1e859cc7c87700922924e9a5e5f#l7504
> [4]:
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.dg/reflect/source_location_of1.C;h=8ba34dbbaa7b93cf9d0ae1441581d099c538840e;hb=HEAD#l42
> [5]:
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/tree.cc;h=d0e745e8d281afce27f8f3f0e25d5b13a5bdc0eb;hb=HEAD#l15000
> [6]:
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.dg/reflect/source_location_of1.C;h=8ba34dbbaa7b93cf9d0ae1441581d099c538840e;hb=HEAD#l104
> [7]:
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.dg/reflect/source_location_of1.C;h=8ba34dbbaa7b93cf9d0ae1441581d099c538840e;hb=HEAD#l105
Uh. I've not been able to make it work with convert_reflect_constant_arg,
either. How about we go back to the original patch, but with the condition
turned into an assert?
Patch generated with -w.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
With an annotation like [[=func]] gcc ends up calling
handle_annotation_attribute with TREE_VALUE (args) being
a VIEW_CONVERT_EXPR, whose type is a FUNCTION_TYPE. That kind of
annotation value should be decayed before checking if the type is
structural.
PR c++/124177
gcc/cp/ChangeLog:
* tree.cc (handle_annotation_attribute): Decay annotation
values. Turn if !type_dependent_expression_p into an assert.
gcc/testsuite/ChangeLog:
* g++.dg/reflect/annotations15.C: New test.
Co-authored-by: Boris Staletic <[email protected]>
---
gcc/cp/tree.cc | 9 ++++++---
gcc/testsuite/g++.dg/reflect/annotations15.C | 17 +++++++++++++++++
2 files changed, 23 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/reflect/annotations15.C
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 7296f2b5c0d..add2758d12f 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -5918,8 +5918,12 @@ handle_annotation_attribute (tree *node, tree ARG_UNUSED
(name),
*no_add_attrs = true;
return NULL_TREE;
}
- if (!type_dependent_expression_p (TREE_VALUE (args)))
- {
+
+ /* Annotations are treated as late attributes so we shouldn't see
+ anything type-dependent now. */
+ gcc_assert (!type_dependent_expression_p (TREE_VALUE (args)));
+ TREE_VALUE (args) = decay_conversion (TREE_VALUE (args),
tf_warning_or_error);
+
if (!structural_type_p (TREE_TYPE (TREE_VALUE (args))))
{
auto_diagnostic_group d;
@@ -5944,7 +5948,6 @@ handle_annotation_attribute (tree *node, tree ARG_UNUSED
(name),
return NULL_TREE;
}
}
- }
if (!processing_template_decl)
{
location_t loc = EXPR_LOCATION (TREE_VALUE (args));
diff --git a/gcc/testsuite/g++.dg/reflect/annotations15.C
b/gcc/testsuite/g++.dg/reflect/annotations15.C
new file mode 100644
index 00000000000..8030960b0b2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/annotations15.C
@@ -0,0 +1,17 @@
+// PR c++/124177
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+#include <meta>
+
+constexpr int f() { return 42; }
+[[=f]] void g() {}
+
+static_assert (annotations_of (^^g).size () == 1);
+static_assert (extract<int(*)()> (annotations_of (^^g)[0])() == 42);
+
+constexpr int x[5]{};
+[[=x]] void h() {}
+
+static_assert (annotations_of (^^h).size () == 1);
+static_assert (type_of (annotations_of (^^h)[0]) == ^^const int*);
base-commit: 5a16651495171d8e6f60df29757f2b396e30a2d5
--
2.53.0
