[gcc r12-9437] c++: generic lambda, local class, __func__ [PR108242]

[gcc r12-9437] c++: generic lambda, local class, __func__ [PR108242]

[Jason Merrill]

https://gcc.gnu.org/g:890d711a2477119a34cf435f6159b6253b124374

commit r12-9437-g890d711a2477119a34cf435f6159b6253b124374
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Mar 16 15:11:25 2023 -0400

    c++: generic lambda, local class, __func__ [PR108242]
    
    Here we are trying to do name lookup in a deferred instantiation of t() and
    failing to find __func__.  tsubst_expr already tries to instantiate members
    of local classes, but was failing with the partial instantiation of generic
    lambdas.
    
            PR c++/108242
    
    gcc/cp/ChangeLog:
    
            * pt.cc (tsubst_expr) [TAG_DEFN]: Handle partial instantiation.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp1y/lambda-generic-func2.C: New test.

Diff:
---
 gcc/cp/pt.cc                                      |  5 ++++-
 gcc/testsuite/g++.dg/cpp1y/lambda-generic-func2.C | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 4d6c6bfb8cf..a9c57e5d45a 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -19090,7 +19090,10 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
 
     case TAG_DEFN:
       tmp = tsubst (TREE_TYPE (t), args, complain, NULL_TREE);
-      if (CLASS_TYPE_P (tmp))
+      if (dependent_type_p (tmp))
+	/* This is a partial instantiation, try again when full.  */
+	add_stmt (build_min (TAG_DEFN, tmp));
+      else if (CLASS_TYPE_P (tmp))
 	{
 	  /* Local classes are not independent templates; they are
 	     instantiated along with their containing function.  And this
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-func2.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-func2.C
new file mode 100644
index 00000000000..ed541c7812f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-func2.C
@@ -0,0 +1,18 @@
+// PR c++/108242
+// { dg-do compile { target c++14 } }
+
+template<int F>
+void my_fun()
+{
+    [&](auto) {
+        static constexpr char const* fun_name = __func__;
+        struct t
+        {
+            t() { fun_name; };
+        } t1;
+    }(12);
+}
+
+int main() {
+    my_fun<1>();
+}