[Driver] Derive '-external-plugin-path'

When the current toolchain is not a Xcode toolchain, derive
'-external-plugin-path' poinintng Xcode plugins paths, so we can use
plugins in Xcode.

rdar://108624128
(cherry picked from commit 3d8b9c9)

Author: rintaro

lib/Driver/DarwinToolChains.cpp

@@ -212,6 +212,63 @@ static bool findXcodeClangLibPath(const Twine &libName,
   return true;
 }
 
+static bool findXcodeExecutableDir(llvm::SmallVectorImpl<char> &path) {
+  assert(path.empty());
+
+  auto xcrunPath = llvm::sys::findProgramByName("xcrun");
+  if (!xcrunPath.getError()) {
+    // Explicitly ask for the default toolchain so that we don't find a Clang
+    // included with an open-source toolchain.
+    const char *args[] = {"-toolchain", "default", "-f", "swiftc", nullptr};
+    sys::TaskQueue queue;
+    queue.addTask(xcrunPath->c_str(), args, /*Env=*/llvm::None,
+                  /*Context=*/nullptr,
+                  /*SeparateErrors=*/true);
+    queue.execute(nullptr,
+                  [&path](sys::ProcessId PID, int returnCode, StringRef output,
+                          StringRef errors,
+                          sys::TaskProcessInformation ProcInfo,
+                          void *unused) -> sys::TaskFinishedResponse {
+                    if (returnCode == 0) {
+                      output = output.rtrim();
+                      path.append(output.begin(), output.end());
+                      llvm::sys::path::remove_filename(path); // 'swiftc'
+                    }
+                    return sys::TaskFinishedResponse::ContinueExecution;
+                  });
+  }
+
+  return !path.empty();
+}
+
+static bool findCurrentSelectedXcodeDir(llvm::SmallVectorImpl<char> &path) {
+  assert(path.empty());
+
+  auto xcrunPath = llvm::sys::findProgramByName("xcode-select");
+  if (!xcrunPath.getError()) {
+    // Explicitly ask for the default toolchain so that we don't find a Clang
+    // included with an open-source toolchain.
+    const char *args[] = {"-p", nullptr};
+    sys::TaskQueue queue;
+    queue.addTask(xcrunPath->c_str(), args, /*Env=*/llvm::None,
+                  /*Context=*/nullptr,
+                  /*SeparateErrors=*/true);
+    queue.execute(nullptr,
+                  [&path](sys::ProcessId PID, int returnCode, StringRef output,
+                          StringRef errors,
+                          sys::TaskProcessInformation ProcInfo,
+                          void *unused) -> sys::TaskFinishedResponse {
+                    if (returnCode == 0) {
+                      output = output.rtrim();
+                      path.append(output.begin(), output.end());
+                    }
+                    return sys::TaskFinishedResponse::ContinueExecution;
+                  });
+  }
+
+  return !path.empty();
+}
+
 static void addVersionString(const ArgList &inputArgs, ArgStringList &arguments,
                              llvm::VersionTuple version) {
   llvm::SmallString<8> buf;
@@ -601,6 +658,46 @@ void toolchains::Darwin::addCommonFrontendArgs(
     llvm::opt::ArgStringList &arguments) const {
   ToolChain::addCommonFrontendArgs(OI, output, inputArgs, arguments);
 
+  // Pass -external-plugin-path if the current toolchain is not a Xcode default
+  // toolchain.
+  {
+    // 'xcode-select -p'
+    SmallString<256> xcodeDir;
+    if (findCurrentSelectedXcodeDir(xcodeDir) &&
+        !StringRef(getDriver().getSwiftProgramPath()).starts_with(xcodeDir)) {
+
+      // 'xcrun -f swiftc'
+      SmallString<256> xcodeExecutableDir;
+      if (findXcodeExecutableDir(xcodeExecutableDir)) {
+        using namespace llvm::sys;
+
+        // '${toolchain}/usr/bin/swift-plugin-server'
+        SmallString<256> xcodePluginServerPath(xcodeExecutableDir);
+        path::append(xcodePluginServerPath, "swift-plugin-server");
+        if (fs::can_execute(xcodePluginServerPath)) {
+
+          // '${toolchain}/usr/lib/swift/host/plugins'
+          SmallString<256> xcodePluginPath(xcodeExecutableDir);
+          path::remove_filename(xcodePluginPath); // 'bin'
+          path::append(xcodePluginPath, "lib", "swift", "host", "plugins");
+
+          // '${toolchain}/usr/locallib/swift/host/plugins'
+          SmallString<256> xcodeLocalPluginPath(xcodeExecutableDir);
+          path::remove_filename(xcodeLocalPluginPath); // 'bin'
+          path::append(xcodeLocalPluginPath, "local");
+          path::append(xcodeLocalPluginPath, "lib", "swift", "host", "plugins");
+
+          arguments.push_back("-external-plugin-path");
+          arguments.push_back(inputArgs.MakeArgString(xcodePluginPath + "#" +
+                                                      xcodePluginServerPath));
+          arguments.push_back("-external-plugin-path");
+          arguments.push_back(inputArgs.MakeArgString(
+              xcodeLocalPluginPath + "#" + xcodePluginServerPath));
+        }
+      }
+    }
+  }
+
   if (auto sdkVersion = getTargetSDKVersion(getTriple())) {
     arguments.push_back("-target-sdk-version");
     arguments.push_back(inputArgs.MakeArgString(sdkVersion->getAsString()));

lib/Driver/ToolChains.cpp

@@ -377,8 +377,6 @@ void ToolChain::addCommonFrontendArgs(const OutputInfo &OI,
   }
 
   // Add plugin path options.
-  inputArgs.AddAllArgs(arguments, options::OPT_plugin_path);
-
   {
     SmallString<64> pluginPath;
     auto programPath = getDriver().getSwiftProgramPath();