Simplify reporting of invalid config paths

Do this at a well defined point, instead of randomly the first time they're
queried.

src/env.cpp

@@ -730,6 +730,9 @@ void env_init(const struct config_paths_t *paths /* or NULL */) {
 
     init_input();
 
+    // Complain about invalid config paths.
+    path_emit_config_directory_errors(vars);
+
     // Set up universal variables. The empty string means to use the default path.
     assert(s_universal_variables == NULL);
     s_universal_variables = new env_universal_t(L"");

src/path.cpp

@@ -255,8 +255,7 @@ wcstring path_apply_working_directory(const wcstring &path, const wcstring &work
 /// a function) we don't want that subshell to issue the same warnings.
 static void maybe_issue_path_warning(const wcstring &which_dir, const wcstring &custom_error_msg,
                                      bool using_xdg, const wcstring &xdg_var, const wcstring &path,
-                                     int saved_errno) {
-    auto &vars = env_stack_t::globals();
+                                     int saved_errno, env_stack_t &vars) {
     wcstring warning_var_name = L"_FISH_WARNED_" + which_dir;
     if (vars.get(warning_var_name, ENV_GLOBAL | ENV_EXPORT)) {
         return;
@@ -278,74 +277,77 @@ static void maybe_issue_path_warning(const wcstring &which_dir, const wcstring &
     ignore_result(write(STDERR_FILENO, "\n", 1));
 }
 
-static void path_create(wcstring &path, const wcstring &xdg_var, const wcstring &which_dir,
-                        const wcstring &custom_error_msg) {
-    bool path_done = false;
-    bool using_xdg = false;
-    int saved_errno = 0;
+/// The following type wraps up a user's "base" directories, corresponding (conceptually if not
+/// actually) to XDG spec.
+struct base_directory_t {
+    wcstring path{};       /// the path where we attempted to create the directory.
+    bool success{false};   /// whether creating the directory succeeded.
+    int err{0};            /// the error code if creating the directory failed.
+    bool used_xdg{false};  /// whether an XDG variable was used in resolving the direcotry.
+};
 
+/// Attempt to get a base directory, creating it if necessary. If a variable named \p xdg_var is
+/// set, use that directory; otherwise use the path \p non_xdg_homepath rooted in $HOME. \return the
+/// result; see the base_directory_t fields.
+static base_directory_t make_base_directory(const wcstring &xdg_var,
+                                            const wchar_t *non_xdg_homepath) {
     // The vars we fetch must be exported. Allowing them to be universal doesn't make sense and
     // allowing that creates a lock inversion that deadlocks the shell since we're called before
     // uvars are available.
     const auto &vars = env_stack_t::globals();
+    base_directory_t result{};
     const auto xdg_dir = vars.get(xdg_var, ENV_GLOBAL | ENV_EXPORT);
     if (!xdg_dir.missing_or_empty()) {
-        using_xdg = true;
-        path = xdg_dir->as_string() + L"/fish";
-        if (create_directory(path) != -1) {
-            path_done = true;
-        } else {
-            saved_errno = errno;
-        }
+        result.path = xdg_dir->as_string() + L"/fish";
+        result.used_xdg = true;
     } else {
         const auto home = vars.get(L"HOME", ENV_GLOBAL | ENV_EXPORT);
         if (!home.missing_or_empty()) {
-            path = home->as_string() +
-                   (which_dir == L"config" ? L"/.config/fish" : L"/.local/share/fish");
-            if (create_directory(path) != -1) {
-                path_done = true;
-            } else {
-                saved_errno = errno;
-            }
+            result.path = home->as_string() + non_xdg_homepath;
         }
     }
 
-    if (!path_done) {
-        maybe_issue_path_warning(which_dir, custom_error_msg, using_xdg, xdg_var, path,
-                                 saved_errno);
-        path.clear();
+    errno = 0;
+    result.success = !result.path.empty() && create_directory(result.path) != -1;
+    result.err = errno;
+    return result;
 }
 
-    return;
+static const base_directory_t &get_data_directory() {
+    static base_directory_t s_dir = make_base_directory(L"XDG_DATA_HOME", L"/.local/share/fish");
+    return s_dir;
+}
+
+static const base_directory_t &get_config_directory() {
+    static base_directory_t s_dir = make_base_directory(L"XDG_CONFIG_HOME", L"/.config/fish");
+    return s_dir;
+}
+
+void path_emit_config_directory_errors(env_stack_t &vars) {
+    const auto &data = get_data_directory();
+    if (!data.success) {
+        maybe_issue_path_warning(L"data", _(L"Your history will not be saved."), data.used_xdg,
+                                 L"XDG_DATA_HOME", data.path, data.err, vars);
+    }
+
+    const auto &config = get_config_directory();
+    if (!config.success) {
+        maybe_issue_path_warning(L"config", _(L"Your personal settings will not be saved."),
+                                 config.used_xdg, L"XDG_CONFIG_HOME", config.path, config.err,
+                                 vars);
+    }
 }
 
-/// Cache the config path.
 bool path_get_config(wcstring &path) {
-    static bool config_path_done = false;
-    static wcstring config_path(L"");
-
-    if (!config_path_done) {
-        path_create(config_path, L"XDG_CONFIG_HOME", L"config",
-                    _(L"Your personal settings will not be saved."));
-        config_path_done = true;
+    const auto &dir = get_config_directory();
+    path = dir.success ? dir.path : L"";
+    return dir.success;
 }
 
-    path = config_path;
-    return !config_path.empty();
-}
-
-/// Cache the data path.
 bool path_get_data(wcstring &path) {
-    static bool data_path_done = false;
-    static wcstring data_path(L"");
-
-    if (!data_path_done) {
-        data_path_done = true;
-        path_create(data_path, L"XDG_DATA_HOME", L"data", _(L"Your history will not be saved."));
-    }
-
-    path = data_path;
-    return !data_path.empty();
+    const auto &dir = get_data_directory();
+    path = dir.success ? dir.path : L"";
+    return dir.success;
 }
 
 void path_make_canonical(wcstring &path) {

src/path.h

@@ -29,6 +29,11 @@ bool path_get_config(wcstring &path);
 /// \return whether the directory was returned successfully
 bool path_get_data(wcstring &path);
 
+/// Emit any errors if config directories are missing.
+/// Use the given environment stack to ensure this only occurs once.
+class env_stack_t;
+void path_emit_config_directory_errors(env_stack_t &vars);
+
 /// Finds the full path of an executable.
 ///
 /// Args: