[Support] Add path::user_config_directory for $XDG_CONFIG_HOME etc

llvm/include/llvm/Support/Path.h

 void system_temp_directory(bool erasedOnReboot, SmallVectorImpl<char> &result);
 
 /// Get the user's home directory.
 ///
 /// @param result Holds the resulting path name.
 /// @result True if a home directory is set, false otherwise.
 bool home_directory(SmallVectorImpl<char> &result);
 
+/// Get the directory where packages should read user-specific configurations.
+/// e.g. $XDG_CONFIG_HOME.
+///
+/// @param result Holds the resulting path name.
+/// @result True if the appropriate path was determined, it need not exist.
+bool user_config_directory(SmallVectorImpl<char> &result);
+
 /// Get the directory where installed packages should put their
 /// machine-local cache, e.g. $XDG_CACHE_HOME.
 ///
 /// @param result Holds the resulting path name.
 /// @result True if the appropriate path was determined, it need not exist.
 bool cache_directory(SmallVectorImpl<char> &result);
 
 /// Has root name?

llvm/lib/Support/Unix/Path.inc

if (ConfLen > 0) {
     }
 
     Result.clear();
   }
   #endif
   return false;
 }
 
+bool user_config_directory(SmallVectorImpl<char> &result) {
+#ifdef __APPLE__
+  // Mac: ~/Library/Preferences/
+  if (home_directory(result)) {
+    append("Library", "Preferences");
+    return true;
+  }
+#else
+  // XDG_CONFIG_HOME as defined in the XDG Base Directory Specification:
+  // http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
+  if (const char *RequestedDir = getenv("XDG_CONFIG_HOME")) {
+    result.clear();
+    result.append(RequestedDir, RequestedDir + strlen(RequestedDir));
+    return true;
+  }
+#endif
+  // Fallback: ~/.config
+  if (!home_directory(result)) {
+    return false;
+  }
+  append(result, ".config");
+  return true;
+}
+
 bool cache_directory(SmallVectorImpl<char> &result) {
 #ifdef __APPLE__
   if (getDarwinConfDir(false/*tempDir*/, result)) {
     return true;
   }
 #else
   // XDG_CACHE_HOME as defined in the XDG Base Directory Specification:
   // http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

llvm/lib/Support/Windows/Path.inc

static bool getKnownFolderPath(KNOWNFOLDERID folderId,
   ::CoTaskMemFree(path);
   return ok;
 }
 
 bool home_directory(SmallVectorImpl<char> &result) {
   return getKnownFolderPath(FOLDERID_Profile, result);
 }
 
+bool user_config_directory(SmallVectorImpl<char> &result) {
+  // Either local or roaming appdata may be suitable in some cases, depending
+  // on the data. Local is more conservative, Roaming may not always be correct.
+  return getKnownFolderPath(FOLDERID_LocalAppData, 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;
   do {

llvm/unittests/Support/Path.cpp

TEST(Support, HomeDirectoryWithNoEnv) {
   if (!pw || !pw->pw_dir) return;
   std::string PwDir = pw->pw_dir;
 
   SmallString<128> HomeDir;
   EXPECT_TRUE(path::home_directory(HomeDir));
   EXPECT_EQ(PwDir, HomeDir);
 }
 
+TEST(Support, ConfigDirectoryWithEnv) {
+  WithEnv Env("XDG_CONFIG_HOME", "/xdg/config");
+
+  SmallString<128> ConfigDir;
+  EXPECT_TRUE(path::user_config_directory(ConfigDir));
+  EXPECT_EQ("/xdg/config", ConfigDir);
+}
+
+TEST(Support, ConfigDirectoryNoEnv) {
+  WithEnv Env("XDG_CONFIG_HOME", nullptr);
+
+  SmallString<128> Fallback;
+  ASSERT_TRUE(path::home_directory(Fallback));
+  path::append(Fallback, ".config");
+
+  SmallString<128> CacheDir;
+  EXPECT_TRUE(path::user_config_directory(CacheDir));
+  EXPECT_EQ(Fallback, CacheDir);
+}
+
 TEST(Support, CacheDirectoryWithEnv) {
   WithEnv Env("XDG_CACHE_HOME", "/xdg/cache");
 
   SmallString<128> CacheDir;
   EXPECT_TRUE(path::cache_directory(CacheDir));
   EXPECT_EQ("/xdg/cache", CacheDir);
 }
 
 TEST(Support, CacheDirectoryNoEnv) {
   WithEnv Env("XDG_CACHE_HOME", nullptr);
 
   SmallString<128> Fallback;
   ASSERT_TRUE(path::home_directory(Fallback));
   path::append(Fallback, ".cache");
 
   SmallString<128> CacheDir;
   EXPECT_TRUE(path::cache_directory(CacheDir));
   EXPECT_EQ(Fallback, CacheDir);
 }
 #endif
 
+#ifdef __APPLE__
+TEST(Support, ConfigDirectory) {
+  SmallString<128> Fallback;
+  ASSERT_TRUE(path::home_directory(Fallback));
+  path::append(Fallback, "Library/Preferences");
+
+  SmallString<128> ConfigDir;
+  EXPECT_TRUE(path::user_config_directory(ConfigDir));
+  EXPECT_EQ(Fallback, ConfigDir);
+}
+#endif
+
 #ifdef _WIN32
+TEST(Support, ConfigDirectory) {
+  std::string Expected = getEnvWin(L"LOCALAPPDATA");
+  // Do not try to test it if we don't know what to expect.
+  if (!Expected.empty()) {
+    SmallString<128> CacheDir;
+    EXPECT_TRUE(path::user_config_directory(CacheDir));
+    EXPECT_EQ(Expected, CacheDir);
+  }
+}
+
 TEST(Support, CacheDirectory) {
   std::string Expected = getEnvWin(L"LOCALAPPDATA");
   // Do not try to test it if we don't know what to expect.
   if (!Expected.empty()) {
     SmallString<128> CacheDir;
     EXPECT_TRUE(path::cache_directory(CacheDir));
     EXPECT_EQ(Expected, CacheDir);
   }