[c++20] P0780R2: Support pack-expansion of init-captures.

This permits an init-capture to introduce a new pack:

  template<typename ...T> auto x = [...a = T()] { /* a is a pack */ };

To support this, the mechanism for allowing ParmVarDecls to be packs has
been extended to support arbitrary local VarDecls.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@361300 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 39 insertions, 0 deletions

diff --git a/test/CXX/temp/temp.decls/temp.variadic/init-capture.cpp b/test/CXX/temp/temp.decls/temp.variadic/init-capture.cpp
new file mode 100644
index 0000000000..4d5b6b4745
--- /dev/null
+++ b/test/CXX/temp/temp.decls/temp.variadic/init-capture.cpp
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+namespace p3 {
+  void bar(...);
+  template <typename... Args> void foo(Args... args) {
+    (void)[... xs = args] {
+      bar(xs...);
+    };
+  }
+
+  void use() {
+    foo();
+    foo(1);
+  }
+}
+
+template<typename ...T> void f(T ...t) {
+  (void)[&...x = t] {
+    x; // expected-error {{unexpanded parameter pack 'x'}}
+  };
+
+  // Not OK: can't expand 'x' outside its scope.
+  weird((void)[&...x = t] {
+    return &x; // expected-error {{unexpanded parameter pack 'x'}}
+  }...         // expected-error {{does not contain any unexpanded}}
+  );
+
+  // OK, capture only one 'slice' of 'x'.
+  weird((void)[&x = t] {
+    return &x;
+  }...
+  );
+
+  // 'x' is not expanded by the outer '...', but 'T' is.
+  weird((void)[&... x = t] {
+    return T() + &x; // expected-error {{unexpanded parameter pack 'x'}}
+  }...               // expected-error {{does not contain any unexpanded}}
+  );
+}