Tests: Refactor client of the lazy_typecheck module into a shared input.

This allows the ModuleInterface test to attempt to build a client against the
emitted `.swiftinterface` which will help us ensure the emitted interface is
correct.

Author: tshortli

test/Inputs/lazy_typecheck.swift

@@ -22,7 +22,7 @@ func internalFunc() -> DoesNotExist { // expected-error {{cannot find type 'Does
 }
 
 @inlinable func inlinableFunc() -> Int {
-  return true // expected-error {{cannot convert return expression of type 'Bool' to return type 'Int'}}
+  return 1
 }
 
 private func privateFunc() -> DoesNotExist { // expected-error {{cannot find type 'DoesNotExist' in scope}}

test/Inputs/lazy_typecheck_client.swift

@@ -0,0 +1,25 @@
+// This source file contains an example client of all the public declarations
+// exposed by the library implemented in lazy_typecheck.swift.
+
+import lazy_typecheck
+
+struct ConformsToPublicProto: PublicProto {
+  func req() -> Int { return 1 }
+}
+
+func testGlobalFunctions() {
+  _ = publicFunc()
+  _ = publicFuncWithDefaultArg()
+  #if TEST_PACKAGE
+  _ = packageFunc()
+  #endif
+  constrainedGenericPublicFunction(ConformsToPublicProto())
+  if #available(SwiftStdlib 5.1, *) {
+    _ = publicFuncWithOpaqueReturnType()
+    _ = publicAEICFuncWithOpaqueReturnType()
+  }
+}
+
+func testPublicStruct(_ s: PublicStruct) {
+  _ = s.publicMethod()
+}

test/ModuleInterface/lazy-typecheck.swift

@@ -3,12 +3,15 @@
 // RUN: %target-swift-frontend -swift-version 5 %S/../Inputs/lazy_typecheck.swift -module-name lazy_typecheck -emit-module -emit-module-path /dev/null -emit-module-interface-path %t/lazy_typecheck.swiftinterface -enable-library-evolution -parse-as-library -package-name Package -experimental-lazy-typecheck -experimental-skip-all-function-bodies -experimental-serialize-external-decls-only
 // RUN: %FileCheck %s < %t/lazy_typecheck.swiftinterface
 
+// RUN: rm -rf %t/*.swiftmodule
+// RUN: %target-swift-frontend -package-name Package -typecheck %S/../Inputs/lazy_typecheck_client.swift -I %t
+
 // CHECK: import Swift
 
 // CHECK:       public func publicFunc() -> Swift.Int
 // CHECK:       publicFuncWithDefaultArg(_ x: Swift.Int = 1) -> Swift.Int
 // CHECK:       @inlinable internal func inlinableFunc() -> Swift.Int {
-// CHECK-NEXT:    return true // expected-error {{[{][{]}}cannot convert return expression of type 'Bool' to return type 'Int'{{[}][}]}}
+// CHECK-NEXT:    return 1
 // CHECK-NEXT:  }
 // CHECK:       public func constrainedGenericPublicFunction<T>(_ t: T) where T : lazy_typecheck.PublicProto
 // CHECK:       @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)

test/Serialization/serialize-external-decls-only-lazy-typecheck.swift

@@ -1,25 +1,5 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -swift-version 5 %S/../Inputs/lazy_typecheck.swift -enable-library-evolution -parse-as-library -package-name Package -typecheck -verify
 // RUN: %target-swift-frontend -swift-version 5 %S/../Inputs/lazy_typecheck.swift -module-name lazy_typecheck -emit-module -emit-module-path %t/lazy_typecheck.swiftmodule -enable-library-evolution -parse-as-library -package-name Package -experimental-lazy-typecheck -experimental-skip-all-function-bodies -experimental-serialize-external-decls-only
-// RUN: %target-swift-frontend -package-name Package -typecheck %s -I %t
 
-import lazy_typecheck
-
-struct ConformsToPublicProto: PublicProto {
-  func req() -> Int { return 1 }
-}
-
-func testGlobalFunctions() {
-  _ = publicFunc()
-  _ = publicFuncWithDefaultArg()
-  _ = packageFunc()
-  constrainedGenericPublicFunction(ConformsToPublicProto())
-  if #available(SwiftStdlib 5.1, *) {
-    _ = publicFuncWithOpaqueReturnType()
-    _ = publicAEICFuncWithOpaqueReturnType()
-  }
-}
-
-func testPublicStruct(_ s: PublicStruct) {
-  _ = s.publicMethod()
-}
+// RUN: %target-swift-frontend -package-name Package -typecheck %S/../Inputs/lazy_typecheck_client.swift -D TEST_PACKAGE -I %t