Add an opaque field for necessary bindings struct

Without this, offsets of captures in closure contexts may be
incorrect if there is a non-empty necessary bindings structure
at the front.

rdar://problem/26312900

Author: bitjammer

include/swift/Reflection/ReflectionContext.h

@@ -331,6 +331,10 @@ class ReflectionContext
     // Initialize the builder.
     Builder.addField(OffsetToFirstCapture.second, sizeof(StoredPointer));
 
+    // Skip the closure's necessary bindings struct, if it's present.
+    auto SizeOfNecessaryBindings = Info.NumBindings * sizeof(StoredPointer);
+    Builder.addField(SizeOfNecessaryBindings, sizeof(StoredPointer));
+
     // FIXME: should be unordered_set but I'm too lazy to write a hash
     // functor
     std::set<std::pair<const TypeRef *, const MetadataSource *>> Done;

validation-test/Reflection/functions.swift

@@ -76,21 +76,21 @@ func generic<T : P, U, V : C>(x: T, y: U, z: V, i: Int) {
 // CHECK-NEXT:    (builtin Builtin.NativeObject)
 
 // CHECK-32:      Type info:
-// CHECK-32-NEXT: (closure_context size=24 alignment=4 stride=24 num_extra_inhabitants=0
-// CHECK-32-NEXT:   (field offset=12
+// CHECK-32-NEXT: (closure_context size=40 alignment=4 stride=40 num_extra_inhabitants=0
+// CHECK-32-NEXT:   (field offset=28
 // CHECK-32-NEXT:     (reference kind=strong refcounting=native))
-// CHECK-32-NEXT:   (field offset=16
+// CHECK-32-NEXT:   (field offset=32
 // CHECK-32-NEXT:     (reference kind=strong refcounting=native))
-// CHECK-32-NEXT:   (field offset=20
+// CHECK-32-NEXT:   (field offset=36
 // CHECK-32-NEXT:     (reference kind=strong refcounting=native)))
 
 // CHECK-64:      Type info:
-// CHECK-64-NEXT: (closure_context size=40 alignment=8 stride=40 num_extra_inhabitants=0
-// CHECK-64-NEXT:   (field offset=16
+// CHECK-64-NEXT: (closure_context size=72 alignment=8 stride=72 num_extra_inhabitants=0
+// CHECK-64-NEXT:   (field offset=48
 // CHECK-64-NEXT:     (reference kind=strong refcounting=native))
-// CHECK-64-NEXT:   (field offset=24
+// CHECK-64-NEXT:   (field offset=56
 // CHECK-64-NEXT:     (reference kind=strong refcounting=native))
-// CHECK-64-NEXT:   (field offset=32
+// CHECK-64-NEXT:   (field offset=64
 // CHECK-64-NEXT:     (reference kind=strong refcounting=native)))
 }