PR42104: Support instantiations of lambdas that implicitly capture

packs.

Two changes:
 * Track odr-use via FunctionParmPackExprs to properly handle dependent
   odr-uses of packs in generic lambdas.
 * Do not instantiate implicit captures; instead, regenerate them by
   instantiating the body of the lambda. This is necessary to
   distinguish between cases where only one element of a pack is
   captured and cases where the entire pack is captured.

This reinstates r362358 (reverted in r362375) with a fix for an
uninitialized variable use in UpdateMarkingForLValueToRValue.

llvm-svn: 362531

1 files changed, 17 insertions, 0 deletions

diff --git a/clang/test/SemaTemplate/lambda-capture-pack.cpp b/clang/test/SemaTemplate/lambda-capture-pack.cpp
new file mode 100644
index 00000000000..2fe576769db
--- /dev/null
+++ b/clang/test/SemaTemplate/lambda-capture-pack.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+// expected-no-diagnostics
+
+template<typename ...T, typename ...Lambda> void check_sizes(Lambda ...L) {
+  static_assert(((sizeof(T) == sizeof(Lambda)) && ...));
+}
+
+template<typename ...T> void f(T ...v) {
+  // Pack expansion of lambdas: each lambda captures only one pack element.
+  check_sizes<T...>([=] { (void)&v; } ...);
+
+  // Pack expansion inside lambda: captures all pack elements.
+  auto l = [=] { ((void)&v, ...); };
+  static_assert(sizeof(l) >= (sizeof(T) + ...));
+}
+
+template void f(int, char, double);