[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.

llvm-svn: 361300

5 files changed, 125 insertions, 5 deletions

diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/expr.prim.lambda.capture/p17.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/expr.prim.lambda.capture/p17.cpp
new file mode 100644
index 00000000000..e2bd513aeff
--- /dev/null
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/expr.prim.lambda.capture/p17.cpp
@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+namespace std_example {
+  namespace std { template<typename T> T &&move(T &); }
+
+  void g(...);
+
+  template <class... Args> void f(Args... args) {
+    auto lm = [&, args...] { return g(args...); };
+    lm();
+
+    auto lm2 = [... xs = std::move(args)] { return g(xs...); };
+    lm2();
+  }
+}
+
+template<typename ...T> constexpr int f(int k, T ...t) {
+  auto a = [...v = t] (bool b) mutable {
+    if (!b) {
+      ((v += 1), ...);
+      return (__SIZE_TYPE__)0;
+    }
+    return (v * ... * 1) + sizeof...(v);
+  };
+  for (int i = 0; i != k; ++i)
+    a(false);
+  return a(true);
+}
+
+static_assert(f(1, 2, 3, 4) == 3 * 4 * 5 + 3);
+static_assert(f(5) == 1);
+
+auto q = [...x = 0] {}; // expected-error {{does not contain any unexpanded parameter packs}}
+
+template<typename ...T> constexpr int nested(T ...t) {
+  return [...a = t] {
+    return [a...] {
+      return (a + ...);
+    }();
+  }();
+}
+static_assert(nested(1, 2, 3) == 6);
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p23.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p23.cpp
index 4ae34dec3e3..028fcee5fda 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p23.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p23.cpp
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 -fsyntax-only -std=c++11 %s -verify -Wno-c++1y-extensions
-// RUN: %clang_cc1 -fsyntax-only -std=c++1y %s -verify
+// RUN: %clang_cc1 -fsyntax-only -std=c++11 %s -verify -Wno-c++1y-extensions -Wno-c++2a-extensions
+// RUN: %clang_cc1 -fsyntax-only -std=c++1y %s -verify -Wno-c++2a-extensions
+// RUN: %clang_cc1 -fsyntax-only -std=c++2a %s -verify
 
 void print();
 
@@ -60,8 +61,25 @@ template void variadic_lambda(int*, float*, double*);
 
 template<typename ...Args>
 void init_capture_pack_err(Args ...args) {
-  [as(args)...] {} (); // expected-error {{expected ','}}
-  [as...(args)]{} (); // expected-error {{expected ','}}
+  [...as(args)]{} ();
+  [as(args)...] {} (); // expected-error {{ellipsis in pack init-capture must appear before the name of the capture}}
+  [as...(args)]{} (); // expected-error {{ellipsis in pack init-capture must appear before the name of the capture}}
+  [...as{args}]{} ();
+  [as{args}...] {} (); // expected-error {{ellipsis in pack init-capture must appear before the name of the capture}}
+  [as...{args}]{} (); // expected-error {{ellipsis in pack init-capture must appear before the name of the capture}}
+  [...as = args]{} ();
+  [as = args...] {} (); // expected-error {{ellipsis in pack init-capture must appear before the name of the capture}}
+  [as... = args]{} (); // expected-error {{ellipsis in pack init-capture must appear before the name of the capture}}
+
+  [&...as(args)]{} ();
+  [...&as(args)]{} (); // expected-error {{ellipsis in pack init-capture must appear before the name of the capture}}
+
+  [args...] {} ();
+  [...args] {} (); // expected-error {{ellipsis in pack capture must appear after the name of the capture}}
+
+  [&args...] {} ();
+  [...&args] {} (); // expected-error {{ellipsis in pack capture must appear after the name of the capture}}
+  [&...args] {} (); // expected-error {{ellipsis in pack capture must appear after the name of the capture}}
 }
 
 template<typename ...Args>
diff --git a/clang/test/CXX/temp/temp.decls/temp.variadic/init-capture.cpp b/clang/test/CXX/temp/temp.decls/temp.variadic/init-capture.cpp
new file mode 100644
index 00000000000..4d5b6b47459
--- /dev/null
+++ b/clang/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}}
+  );
+}
diff --git a/clang/test/FixIt/fixit-c++2a.cpp b/clang/test/FixIt/fixit-c++2a.cpp
new file mode 100644
index 00000000000..c97bb7ae610
--- /dev/null
+++ b/clang/test/FixIt/fixit-c++2a.cpp
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -verify -std=c++2a %s
+// RUN: cp %s %t
+// RUN: not %clang_cc1 -x c++ -std=c++2a -fixit %t
+// RUN: %clang_cc1 -Wall -pedantic -x c++ -std=c++2a %t
+
+/* This is a test of the various code modification hints that only
+   apply in C++2a. */
+template<typename ...T> void init_capture_pack(T ...a) {
+  [x... = a]{}; // expected-error {{must appear before the name}}
+  [x = a...]{}; // expected-error {{must appear before the name}}
+  [...&x = a]{}; // expected-error {{must appear before the name}}
+  [...a]{}; // expected-error {{must appear after the name}}
+  [&...a]{}; // expected-error {{must appear after the name}}
+  [...&a]{}; // expected-error {{must appear after the name}}
+}
diff --git a/clang/test/SemaTemplate/sizeof-pack.cpp b/clang/test/SemaTemplate/sizeof-pack.cpp
index 4b0c883a24a..274726a2315 100644
--- a/clang/test/SemaTemplate/sizeof-pack.cpp
+++ b/clang/test/SemaTemplate/sizeof-pack.cpp
@@ -1,7 +1,13 @@
 // RUN: %clang_cc1 -std=c++11 -verify %s
-// expected-no-diagnostics
 
 template<int &...Ns> int f() {
   return sizeof...(Ns);
 }
 template int f<>();
+
+template<typename ...T> int g() {
+  return [...x = T()] { // expected-warning 2{{extension}}
+    return sizeof...(x);
+  }();
+}
+template int g<>();