Add experimental feature MacrosOnImporters for applying macro to imported decl

This is still very much experimental and we don't want to accidentally
enable it everywhere.

Author: DougGregor

include/swift/Basic/Features.def

@@ -230,6 +230,7 @@ EXPERIMENTAL_FEATURE(NamedOpaqueTypes, false)
 EXPERIMENTAL_FEATURE(FlowSensitiveConcurrencyCaptures, false)
 EXPERIMENTAL_FEATURE(CodeItemMacros, false)
 EXPERIMENTAL_FEATURE(PreambleMacros, false)
+EXPERIMENTAL_FEATURE(MacrosOnImports, true)
 EXPERIMENTAL_FEATURE(TupleConformances, false)
 EXPERIMENTAL_FEATURE(FullTypedThrows, false)
 EXPERIMENTAL_FEATURE(SameElementRequirements, false)

lib/AST/FeatureSet.cpp

@@ -121,6 +121,7 @@ UNINTERESTING_FEATURE(Embedded)
 UNINTERESTING_FEATURE(Volatile)
 UNINTERESTING_FEATURE(SuppressedAssociatedTypes)
 UNINTERESTING_FEATURE(StructLetDestructuring)
+UNINTERESTING_FEATURE(MacrosOnImports)
 
 static bool usesFeatureNonescapableTypes(Decl *decl) {
   auto containsNonEscapable =

lib/AST/NameLookup.cpp

@@ -1722,7 +1722,8 @@ SmallVector<MacroDecl *, 1> namelookup::lookupMacros(DeclContext *dc,
 
     // When resolving macro names for imported entities, we look for any
     // loaded module.
-    if (!moduleDecl && isa<ClangModuleUnit>(moduleScopeDC)) {
+    if (!moduleDecl && isa<ClangModuleUnit>(moduleScopeDC) &&
+        ctx.LangOpts.hasFeature(Feature::MacrosOnImports)) {
       moduleDecl = ctx.getLoadedModule(moduleName.getBaseIdentifier());
       moduleScopeDC = moduleDecl;
     }

test/Macros/expand_on_imported.swift

@@ -7,7 +7,7 @@
 // RUN: %target-swift-frontend -swift-version 5 -emit-module -o %t/macro_library.swiftmodule %S/Inputs/macro_library.swift -module-name macro_library -load-plugin-library %t/%target-library-name(MacroDefinition)
 
 // Diagnostics testing
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify -swift-version 5 -enable-experimental-feature CodeItemMacros -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name ModuleUser %s -I %t
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify -swift-version 5 -enable-experimental-feature MacrosOnImports -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name ModuleUser %s -I %t
 
 import CompletionHandlerGlobals
 import macro_library

test/Macros/expand_on_imported_objc.swift

@@ -7,7 +7,7 @@
 // RUN: %target-swift-frontend -swift-version 5 -emit-module -o %t/macro_library.swiftmodule %S/Inputs/macro_library.swift -module-name macro_library -load-plugin-library %t/%target-library-name(MacroDefinition)
 
 // Diagnostics testing
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify -swift-version 5 -enable-experimental-feature CodeItemMacros -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name ModuleUser %s -I %t
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify -swift-version 5 -enable-experimental-feature MacrosOnImports -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name ModuleUser %s -I %t 
 
 import CompletionHandlerGlobals
 import macro_library

test/Macros/print_clang_expand_on_imported.swift

@@ -6,7 +6,7 @@
 // Build the macro library to give us access to AddAsync.
 // RUN: %target-swift-frontend -swift-version 5 -emit-module -o %t/macro_library.swiftmodule %S/Inputs/macro_library.swift -module-name macro_library -load-plugin-library %t/%target-library-name(MacroDefinition)
 
-// RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -print-module -print-implicit-attrs -source-filename %s -module-to-print=CompletionHandlerGlobals -I %t -function-definitions=false -load-plugin-library %t/%target-library-name(MacroDefinition) -import-module macro_library > %t/imported.printed.txt
+// RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -print-module -print-implicit-attrs -source-filename %s -module-to-print=CompletionHandlerGlobals -I %t -function-definitions=false -load-plugin-library %t/%target-library-name(MacroDefinition) -import-module macro_library -enable-experimental-feature MacrosOnImports > %t/imported.printed.txt
 // RUN: %FileCheck -input-file %t/imported.printed.txt %s
 
 import CompletionHandlerGlobals

test/Macros/print_clang_expand_on_imported_objc.swift

@@ -6,7 +6,7 @@
 // Build the macro library to give us access to AddAsync.
 // RUN: %target-swift-frontend -swift-version 5 -emit-module -o %t/macro_library.swiftmodule %S/Inputs/macro_library.swift -module-name macro_library -load-plugin-library %t/%target-library-name(MacroDefinition)
 
-// RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -print-module -print-implicit-attrs -source-filename %s -module-to-print=CompletionHandlerGlobals -I %t -function-definitions=false -load-plugin-library %t/%target-library-name(MacroDefinition) -import-module macro_library > %t/imported.printed.txt
+// RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -print-module -print-implicit-attrs -source-filename %s -module-to-print=CompletionHandlerGlobals -I %t -function-definitions=false -load-plugin-library %t/%target-library-name(MacroDefinition) -import-module macro_library -enable-experimental-feature MacrosOnImports > %t/imported.printed.txt
 // RUN: %FileCheck -input-file %t/imported.printed.txt %s
 
 import CompletionHandlerGlobals