[Reflection] Add a test for reflecting empty structs.

rdar://problem/56784375

Author: mikeash

validation-test/Reflection/Inputs/EmptyStruct/EmptyStruct.h

@@ -0,0 +1,3 @@
+struct EmptyStructC {
+  int trailing[0];
+};

validation-test/Reflection/Inputs/EmptyStruct/module.map

@@ -0,0 +1,3 @@
+module EmptyStruct {
+  header "EmptyStruct.h"
+}

validation-test/Reflection/reflect_empty_struct.swift

@@ -0,0 +1,74 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -lswiftSwiftReflectionTest -I %S/Inputs/EmptyStruct/ %s -o %t/reflect_empty_struct
+// RUN: %target-codesign %t/reflect_empty_struct
+
+// RUN: %target-run %target-swift-reflection-test %t/reflect_empty_struct | %FileCheck %s --check-prefix=CHECK-%target-ptrsize
+
+// REQUIRES: objc_interop
+// REQUIRES: executable_test
+
+import SwiftReflectionTest
+
+import EmptyStruct
+
+@_alignment(1) struct EmptyStruct { }
+class Class {
+  var a = EmptyStruct()
+  var b: Any = EmptyStruct()
+  var c = EmptyStructC()
+  var d: Any = EmptyStructC()
+}
+
+var obj = Class()
+
+reflect(object: obj)
+
+// CHECK-64: Reflecting an object.
+// CHECK-64: Instance pointer in child address space: 0x{{[0-9a-fA-F]+}}
+// CHECK-64: Type reference:
+// CHECK-64: (class reflect_empty_struct.Class)
+
+// CHECK-64: Type info:
+// CHECK-64: (class_instance size=80 alignment=8 stride=80 num_extra_inhabitants=0 bitwise_takable=1
+// CHECK-64:   (field name=a offset=16
+// CHECK-64:     (struct size=0 alignment=1 stride=1 num_extra_inhabitants=0 bitwise_takable=1))
+// CHECK-64:   (field name=b offset=16
+// CHECK-64:     (opaque_existential size=32 alignment=8 stride=32 num_extra_inhabitants=2147483647 bitwise_takable=1
+// CHECK-64:       (field name=metadata offset=24
+// CHECK-64:         (builtin size=8 alignment=8 stride=8 num_extra_inhabitants=2147483647 bitwise_takable=1))))
+// CHECK-64:   (field name=c offset=48
+// CHECK-64:     (struct size=0 alignment=1 stride=1 num_extra_inhabitants=0 bitwise_takable=1
+// CHECK-64:       (field name=trailing offset=0
+// CHECK-64:         (tuple size=0 alignment=1 stride=1 num_extra_inhabitants=0 bitwise_takable=1))))
+// CHECK-64:   (field name=d offset=48
+// CHECK-64:     (opaque_existential size=32 alignment=8 stride=32 num_extra_inhabitants=2147483647 bitwise_takable=1
+// CHECK-64:       (field name=metadata offset=24
+// CHECK-64:         (builtin size=8 alignment=8 stride=8 num_extra_inhabitants=2147483647 bitwise_takable=1)))))
+
+// CHECK-32: Reflecting an object.
+// CHECK-32: Instance pointer in child address space: 0x{{[0-9a-fA-F]+}}
+// CHECK-32: Type reference:
+// CHECK-32: (class reflect_empty_struct.Class)
+
+// CHECK-32: Type info:
+// CHECK-32: (class_instance size=40 alignment=4 stride=40 num_extra_inhabitants=0 bitwise_takable=1
+// CHECK-32:   (field name=a offset=8
+// CHECK-32:     (struct size=0 alignment=1 stride=1 num_extra_inhabitants=0 bitwise_takable=1))
+// CHECK-32:   (field name=b offset=8
+// CHECK-32:     (opaque_existential size=16 alignment=4 stride=16 num_extra_inhabitants=4096 bitwise_takable=1
+// CHECK-32:       (field name=metadata offset=12
+// CHECK-32:         (builtin size=4 alignment=4 stride=4 num_extra_inhabitants=4096 bitwise_takable=1))))
+// CHECK-32:   (field name=c offset=24
+// CHECK-32:     (struct size=0 alignment=1 stride=1 num_extra_inhabitants=0 bitwise_takable=1
+// CHECK-32:       (field name=trailing offset=0
+// CHECK-32:         (tuple size=0 alignment=1 stride=1 num_extra_inhabitants=0 bitwise_takable=1))))
+// CHECK-32:   (field name=d offset=24
+// CHECK-32:     (opaque_existential size=16 alignment=4 stride=16 num_extra_inhabitants=4096 bitwise_takable=1
+// CHECK-32:       (field name=metadata offset=12
+// CHECK-32:         (builtin size=4 alignment=4 stride=4 num_extra_inhabitants=4096 bitwise_takable=1)))))
+
+doneReflecting()
+
+// CHECK-64: Done.
+
+// CHECK-32: Done.