diff --git a/clang-tools-extra/clangd/ClangdLSPServer.cpp b/clang-tools-extra/clangd/ClangdLSPServer.cpp
--- a/clang-tools-extra/clangd/ClangdLSPServer.cpp
+++ b/clang-tools-extra/clangd/ClangdLSPServer.cpp
@@ -509,7 +509,7 @@
   if (Opts.ResourceDir)
     Mangler.ResourceDir = *Opts.ResourceDir;
   CDB.emplace(BaseCDB.get(), Params.initializationOptions.fallbackFlags,
-              tooling::ArgumentsAdjuster(std::move(Mangler)));
+              std::move(Mangler));
   {
     // Switch caller's context with LSPServer's background context. Since we
     // rather want to propagate information from LSPServer's context into the
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
@@ -8,8 +8,8 @@
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_COMPILECOMMANDS_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_COMPILECOMMANDS_H
 
+#include "GlobalCompilationDatabase.h"
 #include "support/Threading.h"
-#include "clang/Tooling/ArgumentsAdjusters.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include <deque>
@@ -42,11 +42,14 @@
   //  - on mac, find clang and isysroot by querying the `xcrun` launcher
   static CommandMangler detect();
 
-  void adjust(std::vector<std::string> &Cmd, llvm::StringRef File) const;
-  explicit operator clang::tooling::ArgumentsAdjuster() &&;
+  // `Cmd` may describe compilation of a different file, and will be updated
+  // for parsing `TargetFile`.
+  void operator()(tooling::CompileCommand &Cmd,
+                  llvm::StringRef TargetFile) const;
 
 private:
   CommandMangler() = default;
+
   Memoize<llvm::StringMap<std::string>> ResolvedDrivers;
   Memoize<llvm::StringMap<std::string>> ResolvedDriversNoFollow;
 };
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
@@ -13,7 +13,6 @@
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/Options.h"
 #include "clang/Frontend/CompilerInvocation.h"
-#include "clang/Tooling/ArgumentsAdjusters.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLExtras.h"
@@ -195,8 +194,9 @@
 
 CommandMangler CommandMangler::forTests() { return CommandMangler(); }
 
-void CommandMangler::adjust(std::vector<std::string> &Cmd,
-                            llvm::StringRef File) const {
+void CommandMangler::operator()(tooling::CompileCommand &Command,
+                                llvm::StringRef File) const {
+  std::vector<std::string> &Cmd = Command.CommandLine;
   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
@@ -340,16 +340,6 @@
   }
 }
 
-CommandMangler::operator clang::tooling::ArgumentsAdjuster() && {
-  // ArgumentsAdjuster is a std::function and so must be copyable.
-  return [Mangler = std::make_shared<CommandMangler>(std::move(*this))](
-             const std::vector<std::string> &Args, llvm::StringRef File) {
-    auto Result = Args;
-    Mangler->adjust(Result, File);
-    return Result;
-  };
-}
-
 // ArgStripper implementation
 namespace {
 
diff --git a/clang-tools-extra/clangd/GlobalCompilationDatabase.h b/clang-tools-extra/clangd/GlobalCompilationDatabase.h
--- a/clang-tools-extra/clangd/GlobalCompilationDatabase.h
+++ b/clang-tools-extra/clangd/GlobalCompilationDatabase.h
@@ -15,6 +15,7 @@
 #include "support/ThreadsafeFS.h"
 #include "clang/Tooling/ArgumentsAdjusters.h"
 #include "clang/Tooling/CompilationDatabase.h"
+#include "llvm/ADT/FunctionExtras.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringMap.h"
 #include <memory>
@@ -171,12 +172,17 @@
 /// using an in-memory mapping.
 class OverlayCDB : public DelegatingCDB {
 public:
+  // Makes adjustments to a tooling::CompileCommand which will be used to
+  // process a file (possibly different from the one in the command).
+  using CommandMangler = llvm::unique_function<void(tooling::CompileCommand &,
+                                                    StringRef File) const>;
+
   // Base may be null, in which case no entries are inherited.
   // FallbackFlags are added to the fallback compile command.
   // Adjuster is applied to all commands, fallback or not.
   OverlayCDB(const GlobalCompilationDatabase *Base,
              std::vector<std::string> FallbackFlags = {},
-             tooling::ArgumentsAdjuster Adjuster = nullptr);
+             CommandMangler Mangler = nullptr);
 
   llvm::Optional<tooling::CompileCommand>
   getCompileCommand(PathRef File) const override;
@@ -190,7 +196,7 @@
 private:
   mutable std::mutex Mutex;
   llvm::StringMap<tooling::CompileCommand> Commands; /* GUARDED_BY(Mut) */
-  tooling::ArgumentsAdjuster ArgsAdjuster;
+  CommandMangler Mangler;
   std::vector<std::string> FallbackFlags;
 };
 
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
@@ -740,8 +740,8 @@
 
 OverlayCDB::OverlayCDB(const GlobalCompilationDatabase *Base,
                        std::vector<std::string> FallbackFlags,
-                       tooling::ArgumentsAdjuster Adjuster)
-    : DelegatingCDB(Base), ArgsAdjuster(std::move(Adjuster)),
+                       CommandMangler Mangler)
+    : DelegatingCDB(Base), Mangler(std::move(Mangler)),
       FallbackFlags(std::move(FallbackFlags)) {}
 
 llvm::Optional<tooling::CompileCommand>
@@ -757,8 +757,8 @@
     Cmd = DelegatingCDB::getCompileCommand(File);
   if (!Cmd)
     return llvm::None;
-  if (ArgsAdjuster)
-    Cmd->CommandLine = ArgsAdjuster(Cmd->CommandLine, File);
+  if (Mangler)
+    Mangler(*Cmd, File);
   return Cmd;
 }
 
@@ -767,8 +767,8 @@
   std::lock_guard<std::mutex> Lock(Mutex);
   Cmd.CommandLine.insert(Cmd.CommandLine.end(), FallbackFlags.begin(),
                          FallbackFlags.end());
-  if (ArgsAdjuster)
-    Cmd.CommandLine = ArgsAdjuster(Cmd.CommandLine, File);
+  if (Mangler)
+    Mangler(Cmd, File);
   return Cmd;
 }
 
diff --git a/clang-tools-extra/clangd/indexer/IndexerMain.cpp b/clang-tools-extra/clangd/indexer/IndexerMain.cpp
--- a/clang-tools-extra/clangd/indexer/IndexerMain.cpp
+++ b/clang-tools-extra/clangd/indexer/IndexerMain.cpp
@@ -147,7 +147,14 @@
   auto Err = Executor->get()->execute(
       std::make_unique<clang::clangd::IndexActionFactory>(Data),
       clang::tooling::ArgumentsAdjuster(
-          clang::clangd::CommandMangler::detect()));
+          [Mangler = std::make_shared<clang::clangd::CommandMangler>(
+               clang::clangd::CommandMangler::detect())](
+              const std::vector<std::string> &Args, llvm::StringRef File) {
+            clang::tooling::CompileCommand Cmd;
+            Cmd.CommandLine = Args;
+            Mangler->operator()(Cmd, File);
+            return Cmd.CommandLine;
+          }));
   if (Err) {
     clang::clangd::elog("{0}", std::move(Err));
   }
diff --git a/clang-tools-extra/clangd/tool/Check.cpp b/clang-tools-extra/clangd/tool/Check.cpp
--- a/clang-tools-extra/clangd/tool/Check.cpp
+++ b/clang-tools-extra/clangd/tool/Check.cpp
@@ -107,8 +107,7 @@
     if (Opts.ResourceDir)
       Mangler.ResourceDir = *Opts.ResourceDir;
     auto CDB = std::make_unique<OverlayCDB>(
-        BaseCDB.get(), std::vector<std::string>{},
-        tooling::ArgumentsAdjuster(std::move(Mangler)));
+        BaseCDB.get(), std::vector<std::string>{}, std::move(Mangler));
 
     if (auto TrueCmd = CDB->getCompileCommand(File)) {
       Cmd = std::move(*TrueCmd);
diff --git a/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp b/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp
--- a/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp
+++ b/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp
@@ -146,7 +146,7 @@
   MemoryShardStorage MSS(Storage, CacheHits);
   // We need the CommandMangler, because that applies the config we're testing.
   OverlayCDB CDB(/*Base=*/nullptr, /*FallbackFlags=*/{},
-                 tooling::ArgumentsAdjuster(CommandMangler::forTests()));
+                 CommandMangler::forTests());
 
   BackgroundIndex Idx(
       FS, CDB, [&](llvm::StringRef) { return &MSS; }, std::move(Opts));
diff --git a/clang-tools-extra/clangd/unittests/ClangdTests.cpp b/clang-tools-extra/clangd/unittests/ClangdTests.cpp
--- a/clang-tools-extra/clangd/unittests/ClangdTests.cpp
+++ b/clang-tools-extra/clangd/unittests/ClangdTests.cpp
@@ -350,7 +350,7 @@
   Opts.ContextProvider =
       ClangdServer::createConfiguredContextProvider(&CfgProvider, nullptr);
   OverlayCDB CDB(/*Base=*/nullptr, /*FallbackFlags=*/{},
-                 tooling::ArgumentsAdjuster(CommandMangler::forTests()));
+                 CommandMangler::forTests());
   MockFS FS;
   ClangdServer Server(CDB, FS, Opts);
   // foo.cc sees the expected definition, as FOO is defined.
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
@@ -45,41 +45,47 @@
   Mangler.ClangPath = testPath("fake/clang");
   Mangler.ResourceDir = testPath("fake/resources");
   Mangler.Sysroot = testPath("fake/sysroot");
-  std::vector<std::string> Cmd = {"clang++", "--", "foo.cc", "bar.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_THAT(Cmd, ElementsAre(testPath("fake/clang++"),
-                               "-resource-dir=" + testPath("fake/resources"),
-                               "-isysroot", testPath("fake/sysroot"), "--",
-                               "foo.cc"));
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {"clang++", "--", "foo.cc", "bar.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_THAT(Cmd.CommandLine,
+              ElementsAre(testPath("fake/clang++"),
+                          "-resource-dir=" + testPath("fake/resources"),
+                          "-isysroot", testPath("fake/sysroot"), "--",
+                          "foo.cc"));
 }
 
 TEST(CommandMangler, FilenameMismatch) {
   auto Mangler = CommandMangler::forTests();
   Mangler.ClangPath = testPath("clang");
   // Our compile flags refer to foo.cc...
-  std::vector<std::string> Cmd = {"clang", "foo.cc"};
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {"clang", "foo.cc"};
   // but we're applying it to foo.h...
-  Mangler.adjust(Cmd, "foo.h");
+  Mangler(Cmd, "foo.h");
   // so transferCompileCommand should add -x c++-header to preserve semantics.
-  EXPECT_THAT(
-      Cmd, ElementsAre(testPath("clang"), "-x", "c++-header", "--", "foo.h"));
+  EXPECT_THAT(Cmd.CommandLine, ElementsAre(testPath("clang"), "-x",
+                                           "c++-header", "--", "foo.h"));
 }
 
 TEST(CommandMangler, ResourceDir) {
   auto Mangler = CommandMangler::forTests();
   Mangler.ResourceDir = testPath("fake/resources");
-  std::vector<std::string> Cmd = {"clang++", "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_THAT(Cmd, Contains("-resource-dir=" + testPath("fake/resources")));
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {"clang++", "foo.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_THAT(Cmd.CommandLine,
+              Contains("-resource-dir=" + testPath("fake/resources")));
 }
 
 TEST(CommandMangler, Sysroot) {
   auto Mangler = CommandMangler::forTests();
   Mangler.Sysroot = testPath("fake/sysroot");
 
-  std::vector<std::string> Cmd = {"clang++", "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_THAT(llvm::join(Cmd, " "),
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {"clang++", "foo.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_THAT(llvm::join(Cmd.CommandLine, " "),
               HasSubstr("-isysroot " + testPath("fake/sysroot")));
 }
 
@@ -87,21 +93,22 @@
   auto Mangler = CommandMangler::forTests();
   Mangler.ClangPath = testPath("fake/clang");
 
-  std::vector<std::string> Cmd = {"clang++", "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_EQ(testPath("fake/clang++"), Cmd.front());
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {"clang++", "foo.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_EQ(testPath("fake/clang++"), Cmd.CommandLine.front());
 
-  Cmd = {"unknown-binary", "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_EQ(testPath("fake/unknown-binary"), Cmd.front());
+  Cmd.CommandLine = {"unknown-binary", "foo.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_EQ(testPath("fake/unknown-binary"), Cmd.CommandLine.front());
 
-  Cmd = {testPath("path/clang++"), "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_EQ(testPath("path/clang++"), Cmd.front());
+  Cmd.CommandLine = {testPath("path/clang++"), "foo.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_EQ(testPath("path/clang++"), Cmd.CommandLine.front());
 
-  Cmd = {"foo/unknown-binary", "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_EQ("foo/unknown-binary", Cmd.front());
+  Cmd.CommandLine = {"foo/unknown-binary", "foo.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_EQ("foo/unknown-binary", Cmd.CommandLine.front());
 }
 
 // Only run the PATH/symlink resolving test on unix, we need to fiddle
@@ -142,10 +149,11 @@
   // Test the case where the driver is an absolute path to a symlink.
   auto Mangler = CommandMangler::forTests();
   Mangler.ClangPath = testPath("fake/clang");
-  std::vector<std::string> Cmd = {(TempDir + "/bin/foo").str(), "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {(TempDir + "/bin/foo").str(), "foo.cc"};
+  Mangler(Cmd, "foo.cc");
   // Directory based on resolved symlink, basename preserved.
-  EXPECT_EQ((TempDir + "/lib/foo").str(), Cmd.front());
+  EXPECT_EQ((TempDir + "/lib/foo").str(), Cmd.CommandLine.front());
 
   // Set PATH to point to temp/bin so we can find 'foo' on it.
   ASSERT_TRUE(::getenv("PATH"));
@@ -159,21 +167,22 @@
   Mangler = CommandMangler::forTests();
   Mangler.ClangPath = testPath("fake/clang");
   // Driver found on PATH.
-  Cmd = {"foo", "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
+  Cmd.CommandLine = {"foo", "foo.cc"};
+  Mangler(Cmd, "foo.cc");
   // Found the symlink and resolved the path as above.
-  EXPECT_EQ((TempDir + "/lib/foo").str(), Cmd.front());
+  EXPECT_EQ((TempDir + "/lib/foo").str(), Cmd.CommandLine.front());
 
   // Symlink not resolved with -no-canonical-prefixes.
-  Cmd = {"foo", "-no-canonical-prefixes", "foo.cc"};
-  Mangler.adjust(Cmd, "foo.cc");
-  EXPECT_EQ((TempDir + "/bin/foo").str(), Cmd.front());
+  Cmd.CommandLine = {"foo", "-no-canonical-prefixes", "foo.cc"};
+  Mangler(Cmd, "foo.cc");
+  EXPECT_EQ((TempDir + "/bin/foo").str(), Cmd.CommandLine.front());
 }
 #endif
 
 TEST(CommandMangler, ConfigEdits) {
   auto Mangler = CommandMangler::forTests();
-  std::vector<std::string> Cmd = {"clang++", "foo.cc"};
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {"clang++", "foo.cc"};
   {
     Config Cfg;
     Cfg.CompileFlags.Edits.push_back([](std::vector<std::string> &Argv) {
@@ -185,11 +194,11 @@
       Argv = tooling::getInsertArgumentAdjuster("--hello")(Argv, "");
     });
     WithContextValue WithConfig(Config::Key, std::move(Cfg));
-    Mangler.adjust(Cmd, "foo.cc");
+    Mangler(Cmd, "foo.cc");
   }
   // Edits are applied in given order and before other mangling and they always
   // go before filename.
-  EXPECT_THAT(Cmd, ElementsAre(_, "--hello", "--", "FOO.CC"));
+  EXPECT_THAT(Cmd.CommandLine, ElementsAre(_, "--hello", "--", "FOO.CC"));
 }
 
 static std::string strip(llvm::StringRef Arg, llvm::StringRef Argv) {
@@ -363,70 +372,75 @@
 TEST(CommandMangler, InputsAfterDashDash) {
   const auto Mangler = CommandMangler::forTests();
   {
-    std::vector<std::string> Args = {"clang", "/Users/foo.cc"};
-    Mangler.adjust(Args, "/Users/foo.cc");
-    EXPECT_THAT(llvm::makeArrayRef(Args).take_back(2),
+    tooling::CompileCommand Cmd;
+    Cmd.CommandLine = {"clang", "/Users/foo.cc"};
+    Mangler(Cmd, "/Users/foo.cc");
+    EXPECT_THAT(llvm::makeArrayRef(Cmd.CommandLine).take_back(2),
                 ElementsAre("--", "/Users/foo.cc"));
-    EXPECT_THAT(llvm::makeArrayRef(Args).drop_back(2),
+    EXPECT_THAT(llvm::makeArrayRef(Cmd.CommandLine).drop_back(2),
                 Not(Contains("/Users/foo.cc")));
   }
   // In CL mode /U triggers an undef operation, hence `/Users/foo.cc` shouldn't
   // be interpreted as a file.
   {
-    std::vector<std::string> Args = {"clang", "--driver-mode=cl", "bar.cc",
-                                     "/Users/foo.cc"};
-    Mangler.adjust(Args, "bar.cc");
-    EXPECT_THAT(llvm::makeArrayRef(Args).take_back(2),
+    tooling::CompileCommand Cmd;
+    Cmd.CommandLine = {"clang", "--driver-mode=cl", "bar.cc", "/Users/foo.cc"};
+    Mangler(Cmd, "bar.cc");
+    EXPECT_THAT(llvm::makeArrayRef(Cmd.CommandLine).take_back(2),
                 ElementsAre("--", "bar.cc"));
-    EXPECT_THAT(llvm::makeArrayRef(Args).drop_back(2), Not(Contains("bar.cc")));
+    EXPECT_THAT(llvm::makeArrayRef(Cmd.CommandLine).drop_back(2),
+                Not(Contains("bar.cc")));
   }
   // All inputs but the main file is dropped.
   {
-    std::vector<std::string> Args = {"clang", "foo.cc", "bar.cc"};
-    Mangler.adjust(Args, "baz.cc");
-    EXPECT_THAT(llvm::makeArrayRef(Args).take_back(2),
+    tooling::CompileCommand Cmd;
+    Cmd.CommandLine = {"clang", "foo.cc", "bar.cc"};
+    Mangler(Cmd, "baz.cc");
+    EXPECT_THAT(llvm::makeArrayRef(Cmd.CommandLine).take_back(2),
                 ElementsAre("--", "baz.cc"));
     EXPECT_THAT(
-        llvm::makeArrayRef(Args).drop_back(2),
+        llvm::makeArrayRef(Cmd.CommandLine).drop_back(2),
         testing::AllOf(Not(Contains("foo.cc")), Not(Contains("bar.cc"))));
   }
 }
 
 TEST(CommandMangler, StripsMultipleArch) {
   const auto Mangler = CommandMangler::forTests();
-  std::vector<std::string> Args = {"clang", "-arch", "foo",
-                                   "-arch", "bar",   "/Users/foo.cc"};
-  Mangler.adjust(Args, "/Users/foo.cc");
-  EXPECT_EQ(
-      llvm::count_if(Args, [](llvm::StringRef Arg) { return Arg == "-arch"; }),
-      0);
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {"clang", "-arch", "foo", "-arch", "bar", "/Users/foo.cc"};
+  Mangler(Cmd, "/Users/foo.cc");
+  EXPECT_EQ(llvm::count_if(Cmd.CommandLine,
+                           [](llvm::StringRef Arg) { return Arg == "-arch"; }),
+            0);
 
   // Single arch option is preserved.
-  Args = {"clang", "-arch", "foo", "/Users/foo.cc"};
-  Mangler.adjust(Args, "/Users/foo.cc");
-  EXPECT_EQ(
-      llvm::count_if(Args, [](llvm::StringRef Arg) { return Arg == "-arch"; }),
-      1);
+  Cmd.CommandLine = {"clang", "-arch", "foo", "/Users/foo.cc"};
+  Mangler(Cmd, "/Users/foo.cc");
+  EXPECT_EQ(llvm::count_if(Cmd.CommandLine,
+                           [](llvm::StringRef Arg) { return Arg == "-arch"; }),
+            1);
 }
 
 TEST(CommandMangler, EmptyArgs) {
   const auto Mangler = CommandMangler::forTests();
-  std::vector<std::string> Args = {};
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {};
   // Make sure we don't crash.
-  Mangler.adjust(Args, "foo.cc");
+  Mangler(Cmd, "foo.cc");
 }
 
 TEST(CommandMangler, PathsAsPositional) {
   const auto Mangler = CommandMangler::forTests();
-  std::vector<std::string> Args = {
+  tooling::CompileCommand Cmd;
+  Cmd.CommandLine = {
       "clang",
       "--driver-mode=cl",
       "-I",
       "foo",
   };
   // Make sure we don't crash.
-  Mangler.adjust(Args, "a.cc");
-  EXPECT_THAT(Args, Contains("foo"));
+  Mangler(Cmd, "a.cc");
+  EXPECT_THAT(Cmd.CommandLine, Contains("foo"));
 }
 } // namespace
 } // namespace clangd
diff --git a/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp b/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp
--- a/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp
+++ b/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp
@@ -138,11 +138,9 @@
 
 TEST_F(OverlayCDBTest, Adjustments) {
   OverlayCDB CDB(Base.get(), {"-DFallback"},
-                 [](const std::vector<std::string> &Cmd, llvm::StringRef File) {
-                   auto Ret = Cmd;
-                   Ret.push_back(
+                 [](tooling::CompileCommand &Cmd, llvm::StringRef File) {
+                   Cmd.CommandLine.push_back(
                        ("-DAdjust_" + llvm::sys::path::filename(File)).str());
-                   return Ret;
                  });
   // Command from underlying gets adjusted.
   auto Cmd = *CDB.getCompileCommand(testPath("foo.cc"));
diff --git a/clang-tools-extra/clangd/unittests/TestTU.cpp b/clang-tools-extra/clangd/unittests/TestTU.cpp
--- a/clang-tools-extra/clangd/unittests/TestTU.cpp
+++ b/clang-tools-extra/clangd/unittests/TestTU.cpp
@@ -64,7 +64,7 @@
   Argv.push_back(FullFilename);
 
   auto Mangler = CommandMangler::forTests();
-  Mangler.adjust(Inputs.CompileCommand.CommandLine, FullFilename);
+  Mangler(Inputs.CompileCommand, FullFilename);
   Inputs.CompileCommand.Filename = FullFilename;
   Inputs.CompileCommand.Directory = testRoot();
   Inputs.Contents = Code;