[Serialization] Limit per-SDK swiftmodule restriction to tagged compilers

Only production compilers should apply the per-SDK restriction on
loading swiftmodules. Use the "is the compiler tagged" information over
a release build to align with the other main swiftmodule loading
restriction accepting only swiftmodules built by the same tag.

Also use an env var SWIFT_DEBUG_FORCE_SWIFTMODULE_PER_SDK to enable
testing this feature in any compilers.

Author: xymus

lib/Serialization/ModuleFileSharedCore.cpp

@@ -309,6 +309,15 @@ static ValidationInfo validateControlBlock(
     case control_block::SDK_NAME: {
       result.sdkName = blobData;
 
+      // Enable this check for tagged compiler or when the
+      // env var is set (for testing).
+      static const char* forceDebugPreSDKRestriction =
+        ::getenv("SWIFT_DEBUG_FORCE_SWIFTMODULE_PER_SDK");
+      if (version::Version::getCurrentCompilerVersion().empty() &&
+          !forceDebugPreSDKRestriction) {
+        break;
+      }
+
       // The loaded module was built with a compatible SDK if either:
       // * it was the same SDK
       // * or one who's name is a prefix of the clients' SDK name. This expects

test/Serialization/restrict-swiftmodule-to-sdk.swift

@@ -6,26 +6,31 @@
 // RUN: %target-swift-frontend -emit-module %t/Lib.swift -swift-version 5 -target-sdk-name A -o %t/build -parse-stdlib -module-cache-path %t/cache
 
 /// Building Client against SDK A should work fine as expected.
-// RUN: %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name A -I %t/build -parse-stdlib -module-cache-path %t/cache
+// RUN: env SWIFT_DEBUG_FORCE_SWIFTMODULE_PER_SDK=true \
+// RUN:   %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name A -I %t/build -parse-stdlib -module-cache-path %t/cache
 
 /// Build Client against SDK B, this should fail at loading Lib against a different SDK than A.
-// RUN: not %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name B -I %t/build -parse-stdlib -module-cache-path %t/cache 2>&1 | %FileCheck %s -check-prefix=CHECK-AvsB
+// RUN: env SWIFT_DEBUG_FORCE_SWIFTMODULE_PER_SDK=true \
+// RUN:   not %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name B -I %t/build -parse-stdlib -module-cache-path %t/cache 2>&1 | %FileCheck %s -check-prefix=CHECK-AvsB
 // CHECK-AvsB: cannot load module 'Lib' built with SDK 'A' when using SDK 'B': {{.*}}Lib.swiftmodule
 
 /// Build Client against SDK A.Secret, this should accept the SDK as being a super set of A.
-// RUN: %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name A.Secret -I %t/build -parse-stdlib -module-cache-path %t/cache
+// RUN: env SWIFT_DEBUG_FORCE_SWIFTMODULE_PER_SDK=true \
+// RUN:   %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name A.Secret -I %t/build -parse-stdlib -module-cache-path %t/cache
 
 /// Build Lib against SDK C.Secret and Client against SDK C, this should be rejected.
 // RUN: %target-swift-frontend -emit-module %t/Lib.swift -swift-version 5 -target-sdk-name C.Secret -o %t/build -parse-stdlib -module-cache-path %t/cache
-// RUN: not %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name C -I %t/build -parse-stdlib -module-cache-path %t/cache 2>&1 | %FileCheck %s -check-prefix=CHECK-C
+// RUN: env SWIFT_DEBUG_FORCE_SWIFTMODULE_PER_SDK=true \
+// RUN:   not %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name C -I %t/build -parse-stdlib -module-cache-path %t/cache 2>&1 | %FileCheck %s -check-prefix=CHECK-C
 // CHECK-C: cannot load module 'Lib' built with SDK 'C.Secret' when using SDK 'C': {{.*}}Lib.swiftmodule
 
 /// Build a resilient Lib against SDK A, and a client against SDK B.
 /// This should succeed after rebuilding from the swiftinterface.
 // RUN: %empty-directory(%t/cache)
 // RUN: %target-swift-frontend -emit-module %t/Lib.swift -swift-version 5 -target-sdk-name A -o %t/build -parse-stdlib -module-cache-path %t/cache \
 // RUN:   -enable-library-evolution -emit-module-interface-path %t/build/Lib.swiftinterface
-// RUN: %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name B -I %t/build -parse-stdlib -module-cache-path %t/cache \
+// RUN: env SWIFT_DEBUG_FORCE_SWIFTMODULE_PER_SDK=true \
+// RUN:   %target-swift-frontend -typecheck %t/Client.swift -swift-version 5 -target-sdk-name B -I %t/build -parse-stdlib -module-cache-path %t/cache \
 // RUN:   -Rmodule-interface-rebuild 2>&1 | %FileCheck %s -check-prefix=CHECK-AvsB-REBUILD
 // CHECK-AvsB-REBUILD: remark: rebuilding module 'Lib' from interface