From: Jason Merrill <jason@redhat.com>
Date: Fri, 9 Apr 2021 20:43:50 +0000 (-0400)
Subject: c++: pack in base-specifier in lambda [PR100006]
X-Git-Tag: basepoints/gcc-12~154
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e89055f90cff9fb6f565b9374e1ab74f805682fb;p=thirdparty%2Fgcc.git

c++: pack in base-specifier in lambda [PR100006]

Normally cp_parser_base_clause prevents unexpanded packs, but in a lambda
check_for_bare_parameter_packs allows it.  Then we weren't finding the
pack when scanning the lambda body.

This doesn't fix a valid variant like

  template <class... Ts> void sink (Ts&&...);
  template <class... Ts>
  void f() {
    sink ([] { struct S : Ts { }; }...);
  }
  int main() {
    f<int>();
  }

but that's a much bigger project.

gcc/cp/ChangeLog:

	PR c++/100006
	* pt.c (find_parameter_packs_r) [TAG_DEFN]: Look into bases.

gcc/testsuite/ChangeLog:

	PR c++/100006
	* g++.dg/cpp0x/lambda/lambda-variadic13.C: New test.
---

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 01c807be1bb5..b328330038a4 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -4061,6 +4061,15 @@ find_parameter_packs_r (tree *tp, int *walk_subtrees, void* data)
       *walk_subtrees = 0;
       return NULL_TREE;
 
+    case TAG_DEFN:
+      /* Local class, need to look through the whole definition.  */
+      t = TREE_TYPE (t);
+      if (CLASS_TYPE_P (t))
+	for (tree bb : BINFO_BASE_BINFOS (TYPE_BINFO (t)))
+	  cp_walk_tree (&BINFO_TYPE (bb), &find_parameter_packs_r,
+			ppd, ppd->visited);
+      return NULL_TREE;
+
     default:
       return NULL_TREE;
     }
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-variadic13.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-variadic13.C
new file mode 100644
index 000000000000..ac4e631ebb51
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-variadic13.C
@@ -0,0 +1,11 @@
+// PR c++/100006
+// { dg-do compile { target c++14 } }
+
+template <class... Ts>
+void f() {
+  [] { struct S : Ts { }; };	// { dg-error "not expanded" }
+}
+
+int main() {
+  f<>();
+}