Do not load a package module if built from interface

Resolves rdar://104617990

Author: elsh

include/swift/AST/DiagnosticsSema.def

@@ -1005,6 +1005,11 @@ ERROR(module_not_testable,Fatal,
 ERROR(module_not_compiled_for_private_import,none,
       "module %0 was not compiled for private import", (Identifier))
 
+ERROR(package_module_not_compiled_from_source,Fatal,
+      "module %0 is a package module but was built from interface; "
+      "it must be compiled from source instead",
+      (Identifier))
+
 ERROR(import_restriction_conflict,none,
       "module %0 cannot be both "
       "%select{implementation-only|SPI only|exported}1 and "

lib/Serialization/SerializedModuleLoader.cpp

@@ -798,8 +798,14 @@ LoadedFile *SerializedModuleLoaderBase::loadAST(
       M.setABIName(Ctx.getIdentifier(loadedModuleFile->getModuleABIName()));
     if (loadedModuleFile->isConcurrencyChecked())
       M.setIsConcurrencyChecked();
-    if (!loadedModuleFile->getModulePackageName().empty())
+    if (!loadedModuleFile->getModulePackageName().empty()) {
+      if (loadedModuleFile->isBuiltFromInterface()) {
+        Ctx.Diags.diagnose(SourceLoc(),
+                           diag::package_module_not_compiled_from_source,
+                           M.getBaseIdentifier());
+      }
       M.setPackageName(Ctx.getIdentifier(loadedModuleFile->getModulePackageName()));
+    }
     M.setUserModuleVersion(loadedModuleFile->getUserModuleVersion());
     for (auto name: loadedModuleFile->getAllowableClientNames()) {
       M.addAllowableClientName(Ctx.getIdentifier(name));

test/Serialization/load_package_module.swift

@@ -0,0 +1,36 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -module-name LibFromInterface -emit-module -emit-module-interface-path %t/LibFromInterface.swiftinterface -parse-as-library %t/Lib.swift -enable-library-evolution -package-name myPkg -swift-version 5
+// RUN: test -f %t/LibFromInterface.swiftinterface
+// RUN: %FileCheck %s -check-prefix CHECK-LIB < %t/LibFromInterface.swiftinterface
+// CHECK-LIB: -package-name myPkg
+// CHECK-LIB-NOT: func log(level: Int)
+
+// RUN: not %target-swift-frontend -module-name Client1 %t/Client1.swift -emit-module -emit-module-path %t/Client1.swiftmodule -enable-library-evolution -package-name myPkg -I %t 2> %t/result.output
+// RUN: %FileCheck %s -check-prefix CHECK-CLIENT < %t/result.output
+// CHECK-CLIENT: module 'LibFromInterface' is a package module but was built from interface; it must be compiled from source instead
+
+// RUN: %target-swift-frontend -module-name LibFromSource -emit-module -emit-module-path %t/LibFromSource.swiftmodule -parse-as-library %t/Lib.swift -package-name myPkg
+// RUN: test -f %t/LibFromSource.swiftmodule
+
+// RUN: %target-swift-frontend -module-name Client2 %t/Client2.swift -emit-module -emit-module-path %t/Client2.swiftmodule -enable-library-evolution -package-name myPkg -I %t
+// RUN: test -f %t/Client2.swiftmodule
+
+//--- Lib.swift
+package func log(level: Int) {}
+
+//--- Client1.swift
+import LibFromInterface
+
+func someFun() {
+  log(level: 1)
+}
+
+//--- Client2.swift
+import LibFromSource
+
+func someFun() {
+  log(level: 1)
+}
+