[PATCH v2] c++: fix ICE with [[deprecated]] [PR120756]

[Marek Polacek]

On Wed, Jun 25, 2025 at 03:13:25PM -0400, Jason Merrill wrote:
> On 6/25/25 1:28 PM, Marek Polacek wrote:
> > @@ -24604,7 +24604,7 @@ resolve_nondeduced_context (tree orig_expr, 
> > tsubst_flags_t complain)
> >     }
> >         if (good == 1)
> >     {
> > -     mark_used (goodfn);
> > +     mark_used (goodfn, complain);
> 
> Actually, if we're going to pass complain, we should also check the return
> value; the usual pattern is
> 
> >           if (!mark_used (fn, complain) && !(complain & tf_error))
> >             return error_mark_node;

OK, done here:

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
Here we end up with "error reporting routines re-entered" because
resolve_nondeduced_context isn't passing complain to mark_used.

        PR c++/120756

gcc/cp/ChangeLog:

        * pt.cc (resolve_nondeduced_context): Pass complain to mark_used.

gcc/testsuite/ChangeLog:

        * g++.dg/warn/deprecated-22.C: New test.
---
 gcc/cp/pt.cc                              |  3 ++-
 gcc/testsuite/g++.dg/warn/deprecated-22.C | 13 +++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/warn/deprecated-22.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index deb0106b158..c7a0066a11a 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24604,7 +24604,8 @@ resolve_nondeduced_context (tree orig_expr, 
tsubst_flags_t complain)
        }
       if (good == 1)
        {
-         mark_used (goodfn);
+         if (!mark_used (goodfn, complain) && !(complain & tf_error))
+           return error_mark_node;
          expr = goodfn;
          if (baselink)
            expr = build_baselink (BASELINK_BINFO (baselink),
diff --git a/gcc/testsuite/g++.dg/warn/deprecated-22.C 
b/gcc/testsuite/g++.dg/warn/deprecated-22.C
new file mode 100644
index 00000000000..60ee607f717
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/deprecated-22.C
@@ -0,0 +1,13 @@
+// PR c++/120756
+// { dg-do compile { target c++11 } }
+
+struct A {
+    template <long> [[deprecated]] void foo ();
+};
+
+template <long t> [[deprecated]] auto bar () -> decltype (&A::foo<t>);
+
+void foo ()
+{
+  bar<0> ();  // { dg-warning "deprecated" }
+}

base-commit: 5aca8510abea6c3fac3336a7445863db07fd4a06
-- 
2.50.0