Only enable -sdk changes for non-Darwin and use the right -sysroot flag on Windows

Also, disable Serialization/runtime-import-from-sdk again and try out a fix for
the ModuleInterface/swift_build_sdk_interfaces/check-only-mode errors.

Author: finagolfin

lib/Frontend/CompilerInvocation.cpp

@@ -271,7 +271,7 @@ static void updateRuntimeLibraryPaths(SearchPathOptions &SearchPathOpts,
     RuntimeLibraryImportPaths.push_back(std::string(LibPath.str()));
   }
 
-  if (!SearchPathOpts.SkipSDKImportPaths && !SearchPathOpts.getSDKPath().empty()) {
+  if (!SearchPathOpts.SkipSDKImportPaths && Triple.isOSDarwin() && !SearchPathOpts.getSDKPath().empty()) {
     const char *swiftDir = FrontendOpts.UseSharedResourceFolder
       ? "swift" : "swift_static";
 
@@ -284,18 +284,6 @@ static void updateRuntimeLibraryPaths(SearchPathOptions &SearchPathOpts,
 
     LibPath = SearchPathOpts.getSDKPath();
     llvm::sys::path::append(LibPath, "usr", "lib", swiftDir);
-    if (!Triple.isOSDarwin()) {
-      // Use the non-architecture suffixed form with directory-layout
-      // swiftmodules.
-      llvm::sys::path::append(LibPath, getPlatformNameForTriple(Triple));
-      RuntimeLibraryImportPaths.push_back(std::string(LibPath.str()));
-
-      // Compatibility with older releases - use the architecture suffixed form
-      // for pre-directory-layout multi-architecture layout.  Note that some
-      // platforms (e.g. Windows) will use this even with directory layout in
-      // older releases.
-      llvm::sys::path::append(LibPath, swift::getMajorArchitectureName(Triple));
-    }
     RuntimeLibraryImportPaths.push_back(std::string(LibPath.str()));
   }
   SearchPathOpts.setRuntimeLibraryImportPaths(RuntimeLibraryImportPaths);
@@ -2411,7 +2399,7 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts, ArgList &Args,
 
   if (const Arg *A = Args.getLastArg(OPT_resource_dir))
     Opts.RuntimeResourcePath = A->getValue();
-  else if (Args.hasArg(OPT_sdk)) {
+  else if (!Triple.isOSDarwin() && Args.hasArg(OPT_sdk)) {
     llvm::SmallString<128> SDKResourcePath(Opts.getSDKPath());
     llvm::sys::path::append(
         SDKResourcePath, "usr", "lib",

test/ModuleInterface/swift_build_sdk_interfaces/check-only-mode.swift

@@ -1,13 +1,14 @@
 // RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/sdk/usr/lib)
+// RUN: cp -r %test-resource-dir %t/sdk/usr/lib
+// RUN: rm -rf %t/sdk/usr/lib/swift/host
 // RUN: mkdir -p %t/sdk/usr/lib/swift/Normal.swiftmodule
 // RUN: mkdir -p %t/sdk/System/Library/Frameworks/FMWK.framework/Modules/FMWK.swiftmodule
 
 // RUN: echo 'public func normal() {}' | %target-swift-frontend - -emit-module-interface-path %t/sdk/usr/lib/swift/Normal.swiftmodule/%target-swiftinterface-name -emit-module -o /dev/null -module-name Normal
 // RUN: echo 'public func flat() {}' | %target-swift-frontend - -emit-module-interface-path %t/sdk/usr/lib/swift/Flat.swiftinterface -emit-module -o /dev/null -module-name Flat
 // RUN: echo 'public func fmwk() {}' | %target-swift-frontend - -emit-module-interface-path %t/sdk/System/Library/Frameworks/FMWK.framework/Modules/FMWK.swiftmodule/%target-swiftinterface-name -emit-module -o /dev/null -module-name FMWK
 
-// RUN: cp -r %test-resource-dir/shims %t/sdk/usr/lib/swift
-// RUN: ln -s %platform-module-dir %t/sdk/usr/lib/swift
 // RUN: %swift_build_sdk_interfaces -sdk %t/sdk -Fsystem %t/sdk/System/Library/Frameworks -v -o %t/prebuilt -check-only
 // RUN: ls %t/prebuilt | %FileCheck %s
 // CHECK-DAG: Normal.swiftmodule

test/Serialization/runtime-import-from-sdk.swift

@@ -6,16 +6,13 @@
 
 // %t/good-sdk contains a loadable standard library.
 // RUN: %empty-directory(%t/good-sdk)
-// RUN: %empty-directory(%t/good-sdk/usr/lib/swift/%target-sdk-name)
+// RUN: %empty-directory(%t/good-sdk/usr/lib/swift)
 // RUN: cp -r %platform-module-dir/Swift.swiftmodule %t/good-sdk/usr/lib/swift/Swift.swiftmodule
-// RUN: cp -r %platform-module-dir/Swift.swiftmodule %t/good-sdk/usr/lib/swift/%target-sdk-name/Swift.swiftmodule
 
 // %t/bad-sdk contains an invalid standard library that cannot be loaded.
 // RUN: %empty-directory(%t/bad-sdk)
 // RUN: %empty-directory(%t/bad-sdk/usr/lib/swift/Swift.swiftmodule)
-// RUN: %empty-directory(%t/bad-sdk/usr/lib/swift/%target-sdk-name/Swift.swiftmodule)
 // RUN: touch %t/bad-sdk/usr/lib/swift/Swift.swiftmodule/garbage-garbage-garbage.swiftmodule
-// RUN: touch %t/bad-sdk/usr/lib/swift/%target-sdk-name/Swift.swiftmodule/garbage-garbage-garbage.swiftmodule
 
 // %t/empty-toolchain does not contain a standard library.
 // RUN: %empty-directory(%t/empty-toolchain)
@@ -48,6 +45,11 @@
 // We also check that ClangImporter noticed SwiftShims in the toolchain and
 // didn't add a -isystem flag to look in the SDK.
 
+// FIXME: We can't properly test this on a non-Darwin platform because we'll get
+// the same error message for "unloadable standard library" and "no standard
+// library" (https://github.com/apple/swift/issues/52499).
+// REQUIRES: objc_interop
+
 // RUN: %empty-directory(%t/mcp)
 // RUN: not %target-swift-frontend(mock-sdk: -sdk %t/bad-sdk) -resource-dir %t/empty-toolchain/usr/lib/swift -module-cache-path %t/mcp -typecheck %s -dump-clang-diagnostics -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import 2>&1 | %FileCheck --check-prefix CHECK-EMPTY %s
 // CHECK-EMPTY-NOT: '-isystem' '{{.*}}/bad-sdk/usr/lib/swift/shims'