[C++17] Reject shadowing of capture by parameter in lambda

Summary:
This change rejects the shadowing of a capture by a parameter in lambdas in C++17.

```
int main() {
  int a;
  auto f = [a](int a) { return a; };
}
```

results in:

```
main.cpp:3:20: error: a lambda parameter cannot shadow an explicitly captured entity
  auto f = [a](int a) { return a; };
                   ^
main.cpp:3:13: note: variable a is explicitly captured here
  auto f = [a](int a) { return a; };
            ^
```

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: lebedev.ri, erik.pilkington, cfe-commits

Differential Revision: https://reviews.llvm.org/D53595

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@345308 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 0 deletions

diff --git a/test/CXX/drs/dr22xx.cpp b/test/CXX/drs/dr22xx.cpp
index 021707d876..70a26db757 100644
--- a/test/CXX/drs/dr22xx.cpp
+++ b/test/CXX/drs/dr22xx.cpp
@@ -15,3 +15,14 @@ struct AnonBitfieldQualifiers {
   const volatile unsigned i3 : 1;
 };
 }
+
+#if __cplusplus >= 201103L
+namespace dr2211 { // dr2211: 8
+void f() {
+  int a;
+  auto f = [a](int a) { (void)a; }; // expected-error {{a lambda parameter cannot shadow an explicitly captured entity}}
+  // expected-note@-1{{variable 'a' is explicitly captured here}}
+  auto g = [=](int a) { (void)a; };
+}
+}
+#endif