Index: clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp
===================================================================
--- clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp
+++ clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp
@@ -106,15 +106,15 @@
       std::function<llvm::Optional<ProjectInfo>(PathRef)> GetProjectInfo)
       : IndexStorageMapMu(std::make_unique<std::mutex>()),
         GetProjectInfo(std::move(GetProjectInfo)) {
-    llvm::SmallString<128> HomeDir;
-    llvm::sys::path::home_directory(HomeDir);
-    this->HomeDir = HomeDir.str().str();
+    llvm::SmallString<128> CacheDir;
+    llvm::sys::path::cache_directory(CacheDir);
+    this->CacheDir = CacheDir.str().str();
   }
 
   // Creates or fetches to storage from cache for the specified project.
   BackgroundIndexStorage *operator()(PathRef File) {
     std::lock_guard<std::mutex> Lock(*IndexStorageMapMu);
-    Path CDBDirectory = HomeDir;
+    Path CDBDirectory = CacheDir;
     if (auto PI = GetProjectInfo(File))
       CDBDirectory = PI->SourceRoot;
     auto &IndexStorage = IndexStorageMap[CDBDirectory];
@@ -132,7 +132,7 @@
     return std::make_unique<DiskBackedIndexStorage>(CDBDirectory);
   }
 
-  Path HomeDir;
+  Path CacheDir;
 
   llvm::StringMap<std::unique_ptr<BackgroundIndexStorage>> IndexStorageMap;
   std::unique_ptr<std::mutex> IndexStorageMapMu;
Index: llvm/include/llvm/Support/Path.h
===================================================================
--- llvm/include/llvm/Support/Path.h
+++ llvm/include/llvm/Support/Path.h
@@ -368,6 +368,13 @@
 /// @result True if a home directory is set, false otherwise.
 bool home_directory(SmallVectorImpl<char> &result);
 
+/// Get the directory where installed packages should put their
+/// machine-local cache.
+///
+/// @param result Holds the resulting path name.
+/// @result True if the appropriate directory was found.
+bool cache_directory(SmallVectorImpl<char> &result);
+
 /// Has root name?
 ///
 /// root_name != ""
Index: llvm/lib/Support/Unix/Path.inc
===================================================================
--- llvm/lib/Support/Unix/Path.inc
+++ llvm/lib/Support/Unix/Path.inc
@@ -1138,6 +1138,20 @@
   return true;
 }
 
+bool cache_directory(SmallVectorImpl<char> &result) {
+  char *RequestedDir = getenv("XDG_CACHE_HOME");
+  if (RequestedDir) {
+    result.clear();
+    result.append(RequestedDir, RequestedDir + strlen(RequestedDir));
+    return true;
+  }
+  if (!home_directory(result)) {
+    return false;
+  }
+  append(result, ".cache");
+  return true;
+}
+
 static bool getDarwinConfDir(bool TempDir, SmallVectorImpl<char> &Result) {
   #if defined(_CS_DARWIN_USER_TEMP_DIR) && defined(_CS_DARWIN_USER_CACHE_DIR)
   // On Darwin, use DARWIN_USER_TEMP_DIR or DARWIN_USER_CACHE_DIR.
Index: llvm/lib/Support/Windows/Path.inc
===================================================================
--- llvm/lib/Support/Windows/Path.inc
+++ llvm/lib/Support/Windows/Path.inc
@@ -1372,6 +1372,10 @@
   return getKnownFolderPath(FOLDERID_Profile, result);
 }
 
+bool cache_directory(SmallVectorImpl<char> &result) {
+  return getKnownFolderPath(FOLDERID_LocalAppData, result);
+}
+
 static bool getTempDirEnvVar(const wchar_t *Var, SmallVectorImpl<char> &Res) {
   SmallVector<wchar_t, 1024> Buf;
   size_t Size = 1024;
Index: llvm/unittests/Support/Path.cpp
===================================================================
--- llvm/unittests/Support/Path.cpp
+++ llvm/unittests/Support/Path.cpp
@@ -358,6 +358,136 @@
 }
 #endif
 
+TEST(Support, CacheDirectoryWithEnv) {
+
+  std::string expected;
+
+  // The value of the environment variable is set to a non-standard
+  // location for the test, so we have to store the original value
+  // even if it's not set.
+  // Use an std::string to copy the data
+
+#ifdef _WIN32
+  std::wstring OriginalStorage;
+  if (wchar_t const *path = ::_wgetenv(L"XDG_CACHE_HOME")) {
+    OriginalStorage = path;
+  }
+
+  ::_wputenv("XDG_CACHE_HOME", L"C:\\xdg\\cache");
+
+  if (wchar_t const *localAppData = ::_wgetenv(L"LOCALAPPDATA")) {
+    auto pathLen = ::wcslen(path);
+    ArrayRef<char> ref{reinterpret_cast<char const *>(path),
+                       pathLen * sizeof(wchar_t)};
+    convertUTF16ToUTF8String(ref, expected);
+  }
+
+  // LocalAppData should always be set, but better safe than sorry
+  if (!expected.empty()) {
+    SmallString<128> CacheDir;
+    auto status = path::cache_directory(CacheDir);
+    EXPECT_TRUE(status);
+    EXPECT_EQ(expected, CacheDir);
+  }
+
+  if (!OriginalStorage.empty()) {
+    ::_wputenv("XDG_CACHE_HOME", OriginalStorage.c_str());
+  } else {
+    ::_wputenv("XDG_CACHE_HOME", nullptr);
+  }
+#else
+  std::string OriginalStorage;
+  if (char const *path = ::getenv("XDG_CACHE_HOME")) {
+    OriginalStorage = path;
+  }
+
+  expected = "/xdg/cache";
+  ::setenv("XDG_CACHE_HOME", expected.c_str(), 1);
+  EXPECT_EQ(expected, std::string(::getenv("XDG_CACHE_HOME")));
+
+  {
+    SmallString<128> CacheDir;
+    auto status = path::cache_directory(CacheDir);
+    EXPECT_TRUE(status);
+    EXPECT_EQ(expected, CacheDir);
+  }
+
+  if (!OriginalStorage.empty()) {
+    ::setenv("XDG_CACHE_HOME", OriginalStorage.c_str(), 1);
+  } else {
+    ::unsetenv("XDG_CACHE_HOME");
+  }
+#endif
+}
+
+TEST(Support, CacheDirectoryNoEnv) {
+  std::string expected;
+#ifdef _WIN32
+  std::wstring OriginalStorage;
+  if (wchar_t const *path = ::_wgetenv(L"XDG_CACHE_HOME")) {
+    OriginalStorage = path;
+  }
+
+  ::_wputenv("XDG_CACHE_HOME", nullptr);
+  EXPECT_EQ(nullptr, ::_wgetenv("XDG_CACHE_HOME"));
+
+  if (wchar_t const *localAppData = ::_wgetenv(L"LOCALAPPDATA")) {
+    auto pathLen = ::wcslen(path);
+    ArrayRef<char> ref{reinterpret_cast<char const *>(path),
+                       pathLen * sizeof(wchar_t)};
+    convertUTF16ToUTF8String(ref, expected);
+  }
+
+  // LocalAppData should always be set, but better safe than sorry
+  if (!expected.empty()) {
+    SmallString<128> CacheDir;
+    auto status = path::cache_directory(CacheDir);
+    EXPECT_TRUE(status);
+    EXPECT_EQ(expected, CacheDir);
+  }
+
+  if (!OriginalStorage.empty()) {
+    ::_wputenv("XDG_CACHE_HOME", OriginalStorage.c_str());
+  } else {
+    ::_wputenv("XDG_CACHE_HOME", nullptr);
+  }
+#else
+  std::string OriginalStorage;
+  if (char const *path = ::getenv("XDG_CACHE_HOME")) {
+    OriginalStorage = path;
+  }
+
+  ::unsetenv("XDG_CACHE_HOME");
+  EXPECT_EQ(nullptr, ::getenv("XDG_CACHE_HOME"));
+
+  SmallString<128> HomeDir;
+  if (path::home_directory(HomeDir)) {
+    path::append(HomeDir, ".cache");
+    expected = std::string(HomeDir.str());
+  }
+
+  if (!expected.empty()) {
+    SmallString<128> CacheDir;
+    auto status = path::cache_directory(CacheDir);
+    EXPECT_TRUE(status);
+    EXPECT_EQ(expected, CacheDir);
+  }
+
+  {
+    SmallString<128> CacheDir;
+    auto status = path::cache_directory(CacheDir);
+    EXPECT_TRUE(status);
+    EXPECT_EQ(expected, CacheDir);
+  }
+
+  if (!OriginalStorage.empty()) {
+    ::setenv("XDG_CACHE_HOME", OriginalStorage.c_str(), 1);
+  } else {
+    ::unsetenv("XDG_CACHE_HOME");
+  }
+#endif
+}
+
 TEST(Support, TempDirectory) {
   SmallString<32> TempDir;
   path::system_temp_directory(false, TempDir);