Added feature flag ShadowFoundation

Author: iCharlesHu

include/swift/Basic/Features.def

@@ -161,6 +161,9 @@ EXPERIMENTAL_FEATURE(BuiltinMacros, false)
 /// declare an attribute which is discoverable and constructable at runtime.
 EXPERIMENTAL_FEATURE(RuntimeDiscoverableAttrs, false)
 
+/// Whether to allow types from Foundation to be implicitly shadowed
+EXPERIMENTAL_FEATURE(ShadowFoundation, false)
+
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

lib/AST/ASTPrinter.cpp

@@ -3156,6 +3156,10 @@ static bool usesFeatureBuiltinMacros(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureShadowFoundation(Decl *decl) {
+  return false;
+}
+
 static void
 suppressingFeatureNoAsyncAvailability(PrintOptions &options,
                                       llvm::function_ref<void()> action) {

lib/AST/NameLookup.cpp

@@ -660,19 +660,58 @@ static void recordShadowedDeclsAfterTypeMatch(
         }
       }
 
-      // Next, prefer any other module over the Foundation module
-      if (auto foundationModule = ctx.getLoadedModule(ctx.Id_Foundation)) {
-        if ((firstModule == foundationModule) !=
-            (secondModule == foundationModule)) {
-          // If second module is Foundation, then it is shadowed by first
-          if (secondModule == foundationModule) {
-            shadowed.insert(secondDecl);
-            continue;
-          }
+      if (ctx.LangOpts.hasFeature(Feature::ShadowFoundation)) {
+        // If `ShadowFoundation` is enabled, allow all types from Foundation
+        // to be implicitly shadowed.
+        if (auto foundationModule = ctx.getLoadedModule(ctx.Id_Foundation)) {
+          if ((firstModule == foundationModule) !=
+              (secondModule == foundationModule)) {
+            // If second module is Foundation, then it is shadowed by first
+            if (secondModule == foundationModule) {
+              shadowed.insert(secondDecl);
+              continue;
+            }
 
-          // Otherwise, the first declaration is shadowed by the second.
-          shadowed.insert(firstDecl);
-          break;
+            // Otherwise, the first declaration is shadowed by the second.
+            shadowed.insert(firstDecl);
+            break;
+          }
+        }
+      } else {
+        // The Foundation overlay introduced Data.withUnsafeBytes, which is
+        // treated as being ambiguous with SwiftNIO's Data.withUnsafeBytes
+        // extension. Apply a special-case name shadowing rule to use the
+        // latter rather than the former, which be the consequence of a more
+        // significant change to name shadowing in the future.
+        if (auto owningStruct1
+              = firstDecl->getDeclContext()->getSelfStructDecl()) {
+          if (auto owningStruct2
+                = secondDecl->getDeclContext()->getSelfStructDecl()) {
+            if (owningStruct1 == owningStruct2 &&
+                owningStruct1->getName().is("Data") &&
+                isa<FuncDecl>(firstDecl) && isa<FuncDecl>(secondDecl) &&
+                firstDecl->getName() == secondDecl->getName() &&
+                firstDecl->getBaseName().userFacingName() == "withUnsafeBytes") {
+              // If the second module is the Foundation module and the first
+              // is the NIOFoundationCompat module, the second is shadowed by the
+              // first.
+              if (firstDecl->getModuleContext()->getName()
+                    .is("NIOFoundationCompat") &&
+                  secondDecl->getModuleContext()->getName().is("Foundation")) {
+                shadowed.insert(secondDecl);
+                continue;
+              }
+
+              // If it's the other way around, the first declaration is shadowed
+              // by the second.
+              if (secondDecl->getModuleContext()->getName()
+                    .is("NIOFoundationCompat") &&
+                  firstDecl->getModuleContext()->getName().is("Foundation")) {
+                shadowed.insert(firstDecl);
+                break;
+              }
+            }
+          }
         }
       }
 

test/Frontend/foundation-module-shadowing.swift

@@ -1,7 +1,7 @@
 // REQUIRES: objc_interop
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -emit-module -emit-module-path %t/ShadowFoundation.swiftmodule -module-name ShadowFoundation %S/Inputs/ShadowFoundation.swift -disable-availability-checking
-// RUN: %target-typecheck-verify-swift -I %t -disable-availability-checking
+// RUN: %target-typecheck-verify-swift -I %t -disable-availability-checking -enable-experimental-feature ShadowFoundation
 
 import Foundation
 import ShadowFoundation