[Sema] Add a test with a typical use case of package only imports

Author: xymus

test/Sema/package-only-references.swift

@@ -0,0 +1,56 @@
+/// Simple use case of a package only import.
+
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+/// Build the libraries.
+// RUN: %target-swift-frontend -emit-module %t/PackageImportedLib.swift -o %t \
+// RUN:   -swift-version 5 -enable-library-evolution \
+// RUN:   -enable-experimental-feature AccessLevelOnImport
+// RUN: %target-swift-frontend -emit-module %t/PackageLib.swift -o %t \
+// RUN:   -swift-version 5 -enable-library-evolution -I %t \
+// RUN:   -enable-experimental-feature AccessLevelOnImport \
+// RUN:   -package-name MyPackage
+
+/// A client in the same package builds fine.
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   -package-name MyPackage -I %t \
+// RUN:   -enable-experimental-feature AccessLevelOnImport
+
+/// A client outside of the package raises errors.
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   -package-name NotMyPackage -I %t \
+// RUN:   -enable-experimental-feature AccessLevelOnImport -verify
+
+//--- PackageImportedLib.swift
+public struct IndirectType {
+    public init() {}
+    public func someMethod() {}
+}
+public protocol IndirectProtocol {}
+
+//--- PackageLib.swift
+package import PackageImportedLib
+
+package func getIndirectType() -> IndirectType {
+    return IndirectType()
+}
+
+package func packageFunc(a: IndirectType) {
+}
+
+package struct PackageStruct : IndirectProtocol {
+    package init() {}
+
+    package var a = IndirectType()
+}
+
+//--- Client.swift
+public import PackageLib
+
+let t = getIndirectType() // expected-error {{cannot find 'getIndirectType' in scope}}
+t.someMethod()
+packageFunc(a: t) // expected-error {{cannot find 'packageFunc' in scope}}
+
+let s = PackageStruct() // expected-error {{cannot find 'PackageStruct' in scope}}
+s.a.someMethod()