diff --git a/clang-tools-extra/clangd/CompileCommands.h b/clang-tools-extra/clangd/CompileCommands.h
--- a/clang-tools-extra/clangd/CompileCommands.h
+++ b/clang-tools-extra/clangd/CompileCommands.h
@@ -12,6 +12,7 @@
 #include "support/Threading.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/CommandLine.h"
 #include <deque>
 #include <optional>
 #include <string>
@@ -50,10 +51,12 @@
                   llvm::StringRef TargetFile) const;
 
 private:
-  CommandMangler() = default;
+  CommandMangler();
 
   Memoize<llvm::StringMap<std::string>> ResolvedDrivers;
   Memoize<llvm::StringMap<std::string>> ResolvedDriversNoFollow;
+  llvm::cl::TokenizerCallback Tokenizer;
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS;
 };
 
 // Removes args from a command-line in a semantically-aware way.
diff --git a/clang-tools-extra/clangd/CompileCommands.cpp b/clang-tools-extra/clangd/CompileCommands.cpp
--- a/clang-tools-extra/clangd/CompileCommands.cpp
+++ b/clang-tools-extra/clangd/CompileCommands.cpp
@@ -14,6 +14,7 @@
 #include "clang/Driver/Options.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Tooling/CompilationDatabase.h"
+#include "clang/Tooling/Tooling.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
@@ -27,6 +28,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Program.h"
+#include "llvm/TargetParser/Host.h"
 #include <iterator>
 #include <optional>
 #include <string>
@@ -185,6 +187,18 @@
 
 } // namespace
 
+CommandMangler::CommandMangler() {
+  Tokenizer = llvm::Triple(llvm::sys::getProcessTriple()).isOSWindows()
+                  ? llvm::cl::TokenizeWindowsCommandLine
+                  : llvm::cl::TokenizeGNUCommandLine;
+  // FS used for expanding response files.
+  // FIXME: ExpandResponseFiles appears not to provide the usual
+  // thread-safety guarantees, as the access to FS is not locked!
+  // For now, use the real FS, which is known to be threadsafe (if we don't
+  // use/change working directory, which ExpandResponseFiles doesn't).
+  FS = llvm::vfs::getRealFileSystem();
+}
+
 CommandMangler CommandMangler::detect() {
   CommandMangler Result;
   Result.ClangPath = detectClangPath();
@@ -201,9 +215,11 @@
   trace::Span S("AdjustCompileFlags");
   // Most of the modifications below assumes the Cmd starts with a driver name.
   // We might consider injecting a generic driver name like "cc" or "c++", but
-  // a Cmd missing the driver is probably rare enough in practice and errnous.
+  // a Cmd missing the driver is probably rare enough in practice and erroneous.
   if (Cmd.empty())
     return;
+  tooling::addExpandedResponseFiles(Cmd, Command.Directory, Tokenizer, *FS);
+  tooling::addTargetAndModeForProgramName(Cmd, Cmd.front());
   auto &OptTable = clang::driver::getDriverOptTable();
   // OriginalArgs needs to outlive ArgList.
   llvm::SmallVector<const char *, 16> OriginalArgs;
@@ -212,7 +228,7 @@
     OriginalArgs.push_back(S.c_str());
   bool IsCLMode = driver::IsClangCL(driver::getDriverMode(
       OriginalArgs[0], llvm::ArrayRef(OriginalArgs).slice(1)));
-  // ParseArgs propagates missig arg/opt counts on error, but preserves
+  // ParseArgs propagates missing arg/opt counts on error, but preserves
   // everything it could parse in ArgList. So we just ignore those counts.
   unsigned IgnoredCount;
   // Drop the executable name, as ParseArgs doesn't expect it. This means
diff --git a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
--- a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
+++ b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
@@ -244,15 +244,7 @@
 parseJSON(PathRef Path, llvm::StringRef Data, std::string &Error) {
   if (auto CDB = tooling::JSONCompilationDatabase::loadFromBuffer(
           Data, Error, tooling::JSONCommandLineSyntax::AutoDetect)) {
-    // FS used for expanding response files.
-    // FIXME: ExpandResponseFilesDatabase appears not to provide the usual
-    // thread-safety guarantees, as the access to FS is not locked!
-    // For now, use the real FS, which is known to be threadsafe (if we don't
-    // use/change working directory, which ExpandResponseFilesDatabase doesn't).
-    auto FS = llvm::vfs::getRealFileSystem();
-    return tooling::inferTargetAndDriverMode(
-        tooling::inferMissingCompileCommands(
-            expandResponseFiles(std::move(CDB), std::move(FS))));
+    return tooling::inferMissingCompileCommands(std::move(CDB));
   }
   return nullptr;
 }
diff --git a/clang-tools-extra/clangd/test/did-change-configuration-params.test b/clang-tools-extra/clangd/test/did-change-configuration-params.test
--- a/clang-tools-extra/clangd/test/did-change-configuration-params.test
+++ b/clang-tools-extra/clangd/test/did-change-configuration-params.test
@@ -45,13 +45,17 @@
 # CHECK-NEXT:    "uri": "file://{{.*}}/foo.c",
 # CHECK-NEXT:    "version": 0
 # CHECK-NEXT:  }
+---
+{"jsonrpc":"2.0","method":"workspace/didChangeConfiguration","params":{"settings":{"compilationDatabaseChanges":{"/clangd-test/foo.c": {"workingDirectory":"/clangd-test2", "compilationCommand": ["riscv64-unknown-elf-gcc", "-c", "foo.c", "-Wall", "-Werror"]}}}}}
+#      CHECK:  "method": "textDocument/publishDiagnostics",
 #
 # ERR: ASTWorker building file {{.*}}foo.c version 0 with command
 # ERR: [{{.*}}clangd-test2]
 # ERR: clang -c -Wall -Werror {{.*}} -- {{.*}}foo.c
+# ERR: ASTWorker building file {{.*}}foo.c version 0 with command
+# ERR: [{{.*}}clangd-test2]
+# ERR: riscv64-unknown-elf-gcc --target=riscv64-unknown-elf -c -Wall -Werror {{.*}} -- {{.*}}foo.c
 ---
 {"jsonrpc":"2.0","id":5,"method":"shutdown"}
 ---
 {"jsonrpc":"2.0","method":"exit"}
-
-
diff --git a/clang-tools-extra/clangd/unittests/CompileCommandsTests.cpp b/clang-tools-extra/clangd/unittests/CompileCommandsTests.cpp
--- a/clang-tools-extra/clangd/unittests/CompileCommandsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/CompileCommandsTests.cpp
@@ -49,7 +49,7 @@
   Cmd.CommandLine = {"clang++", "--", "foo.cc", "bar.cc"};
   Mangler(Cmd, "foo.cc");
   EXPECT_THAT(Cmd.CommandLine,
-              ElementsAre(testPath("fake/clang++"),
+              ElementsAre(testPath("fake/clang++"), "--driver-mode=g++",
                           "-resource-dir=" + testPath("fake/resources"),
                           "-isysroot", testPath("fake/sysroot"), "--",
                           "foo.cc"));
@@ -197,8 +197,10 @@
     Mangler(Cmd, "foo.cc");
   }
   // Edits are applied in given order and before other mangling and they always
-  // go before filename.
-  EXPECT_THAT(Cmd.CommandLine, ElementsAre(_, "--hello", "--", "FOO.CC"));
+  // go before filename. `--driver-mode=g++` is inserted by mangler and
+  // converted to upper case with other arguments in this test only.
+  EXPECT_THAT(Cmd.CommandLine,
+              ElementsAre(_, "--DRIVER-MODE=G++", "--hello", "--", "FOO.CC"));
 }
 
 static std::string strip(llvm::StringRef Arg, llvm::StringRef Argv) {
diff --git a/clang/include/clang/Tooling/Tooling.h b/clang/include/clang/Tooling/Tooling.h
--- a/clang/include/clang/Tooling/Tooling.h
+++ b/clang/include/clang/Tooling/Tooling.h
@@ -506,6 +506,12 @@
 void addTargetAndModeForProgramName(std::vector<std::string> &CommandLine,
                                     StringRef InvokedAs);
 
+/// Helper function that expands response files in command line.
+void addExpandedResponseFiles(std::vector<std::string> &CommandLine,
+                              llvm::StringRef WorkingDir,
+                              llvm::cl::TokenizerCallback Tokenizer,
+                              llvm::vfs::FileSystem &FS);
+
 /// Creates a \c CompilerInvocation.
 CompilerInvocation *newInvocation(DiagnosticsEngine *Diagnostics,
                                   ArrayRef<const char *> CC1Args,
diff --git a/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp b/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
--- a/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
+++ b/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Tooling/CompilationDatabase.h"
+#include "clang/Tooling/Tooling.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ConvertUTF.h"
@@ -48,28 +49,9 @@
 
 private:
   std::vector<CompileCommand> expand(std::vector<CompileCommand> Cmds) const {
-    for (auto &Cmd : Cmds) {
-      bool SeenRSPFile = false;
-      llvm::SmallVector<const char *, 20> Argv;
-      Argv.reserve(Cmd.CommandLine.size());
-      for (auto &Arg : Cmd.CommandLine) {
-        Argv.push_back(Arg.c_str());
-        if (!Arg.empty())
-          SeenRSPFile |= Arg.front() == '@';
-      }
-      if (!SeenRSPFile)
-        continue;
-      llvm::BumpPtrAllocator Alloc;
-      llvm::cl::ExpansionContext ECtx(Alloc, Tokenizer);
-      llvm::Error Err = ECtx.setVFS(FS.get())
-                            .setCurrentDir(Cmd.Directory)
-                            .expandResponseFiles(Argv);
-      if (Err)
-        llvm::errs() << Err;
-      // Don't assign directly, Argv aliases CommandLine.
-      std::vector<std::string> ExpandedArgv(Argv.begin(), Argv.end());
-      Cmd.CommandLine = std::move(ExpandedArgv);
-    }
+    for (auto &Cmd : Cmds)
+      tooling::addExpandedResponseFiles(Cmd.CommandLine, Cmd.Directory,
+                                        Tokenizer, *FS);
     return Cmds;
   }
 
diff --git a/clang/lib/Tooling/Tooling.cpp b/clang/lib/Tooling/Tooling.cpp
--- a/clang/lib/Tooling/Tooling.cpp
+++ b/clang/lib/Tooling/Tooling.cpp
@@ -43,6 +43,7 @@
 #include "llvm/Option/OptTable.h"
 #include "llvm/Option/Option.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
@@ -299,6 +300,31 @@
   }
 }
 
+void addExpandedResponseFiles(std::vector<std::string> &CommandLine,
+                              llvm::StringRef WorkingDir,
+                              llvm::cl::TokenizerCallback Tokenizer,
+                              llvm::vfs::FileSystem &FS) {
+  bool SeenRSPFile = false;
+  llvm::SmallVector<const char *, 20> Argv;
+  Argv.reserve(CommandLine.size());
+  for (auto &Arg : CommandLine) {
+    Argv.push_back(Arg.c_str());
+    if (!Arg.empty())
+      SeenRSPFile |= Arg.front() == '@';
+  }
+  if (!SeenRSPFile)
+    return;
+  llvm::BumpPtrAllocator Alloc;
+  llvm::cl::ExpansionContext ECtx(Alloc, Tokenizer);
+  llvm::Error Err =
+      ECtx.setVFS(&FS).setCurrentDir(WorkingDir).expandResponseFiles(Argv);
+  if (Err)
+    llvm::errs() << Err;
+  // Don't assign directly, Argv aliases CommandLine.
+  std::vector<std::string> ExpandedArgv(Argv.begin(), Argv.end());
+  CommandLine = std::move(ExpandedArgv);
+}
+
 } // namespace tooling
 } // namespace clang
 
@@ -684,7 +710,7 @@
 
   if (!Invocation.run())
     return nullptr;
- 
+
   assert(ASTs.size() == 1);
   return std::move(ASTs[0]);
 }