[Serialization] Disable deserialization safety when testing is enabled

Resilient modules with testing enabled expose internal non-resilient
internal types. These types cannot be reliably used by testable clients
if they don't have all of their members known. For this reason, this
disabled deserialization safety in modules when testing is enabled.

rdar://104923020

Author: xymus

lib/Serialization/Serialization.cpp

@@ -3136,11 +3136,6 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
     if (accessScope.isPublic())
       return true;
 
-    // Testable allows access to internal details.
-    if (value->getDeclContext()->getParentModule()->isTestingEnabled() &&
-        accessScope.isInternal())
-      return true;
-
     if (auto accessor = dyn_cast<AccessorDecl>(value))
       // Accessors are as safe as their storage.
       if (isDeserializationSafe(accessor->getStorage()))
@@ -3189,7 +3184,8 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
 #endif
 
     // Private imports allow safe access to everything.
-    if (DC->getParentModule()->arePrivateImportsEnabled())
+    if (DC->getParentModule()->arePrivateImportsEnabled() ||
+        DC->getParentModule()->isTestingEnabled())
       return;
 
     // Ignore things with no access level.

test/Serialization/Safety/unsafe-decls.swift

@@ -11,7 +11,7 @@
 // RUN:   -enable-library-evolution -swift-version 5 \
 // RUN:   -Xllvm -debug-only=Serialization \
 // RUN:   -enable-testing 2>&1 \
-// RUN:   | %FileCheck --check-prefixes=SAFETY-PRIVATE,NO-SAFETY-INTERNAL-NOT %s
+// RUN:   | %FileCheck --check-prefixes=DISABLED %s
 
 /// Don't mark decls as unsafe when private import is enabled.
 // RUN: %target-swift-frontend -emit-module %s \

test/Serialization/Safety/unsafe-extensions.swift

@@ -11,7 +11,7 @@
 // RUN:   -enable-library-evolution -swift-version 5 \
 // RUN:   -Xllvm -debug-only=Serialization \
 // RUN:   -enable-testing 2>&1 \
-// RUN:   | %FileCheck --check-prefixes=SAFETY-PRIVATE,NO-SAFETY-INTERNAL %s
+// RUN:   | %FileCheck --check-prefixes=DISABLED %s
 
 /// Don't mark decls as unsafe when private import is enabled.
 // RUN: %target-swift-frontend -emit-module %s \