add test for cross-import overlay symbol graphs

Author: QuietMisdreavus

test/SymbolGraph/Module/CrossImport.swift

@@ -0,0 +1,21 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %S/Inputs/CrossImport/A.swift -I %t -module-name A -emit-module -emit-module-path %t/
+// RUN: %target-build-swift %S/Inputs/CrossImport/B.swift -I %t -module-name B -emit-module -emit-module-path %t/
+// RUN: %target-build-swift %s -module-name _A_B -I %t -emit-module -emit-module-path %t/
+// RUN: cp -r %S/Inputs/CrossImport/A.swiftcrossimport %t/
+// RUN: %target-swift-symbolgraph-extract -module-name A -I %t -pretty-print -output-dir %t
+// RUN: %FileCheck %s --input-file %t/[email protected]
+
+@_exported import A
+import B
+
+extension A {
+    public func transmogrify() -> B {
+        return B(y: self.x);
+    }
+}
+
+// CHECK: module
+// CHECK-NEXT: "name": "A"
+// CHECK-NEXT: bystanders
+// CHECK-NEXT:   B

test/SymbolGraph/Module/Inputs/CrossImport/A.swift

@@ -0,0 +1,3 @@
+public struct A {
+    public var x: Int
+}

test/SymbolGraph/Module/Inputs/CrossImport/A.swiftcrossimport/B.swiftoverlay

@@ -0,0 +1,5 @@
+%YAML 1.2
+---
+version: 1
+modules:
+  - name: _A_B

test/SymbolGraph/Module/Inputs/CrossImport/B.swift

@@ -0,0 +1,7 @@
+public struct B {
+    public var y: Int
+
+    public init(y: Int) {
+        self.y = y
+    }
+}