XDG: Windows: resolve $LOCALAPPDATA, $TEMP (#5278)

After #4964 environment variables in the XDG "fallback" table are no
longer expanded.

Fallback to correctly expanded $LOCALAPPDATA, $TEMP. If that fails
(unlikely), fallback to hard-coded paths (e.g. ~/AppData/Local).

Closes #5255

1 files changed, 22 insertions, 6 deletions

diff --git a/src/nvim/os/stdpaths.c b/src/nvim/os/stdpaths.c
index 10b3f4c091..afb9bdec31 100644
--- a/src/nvim/os/stdpaths.c
+++ b/src/nvim/os/stdpaths.c
@@ -16,20 +16,29 @@ static const char *xdg_env_vars[] = {
   [kXDGDataDirs] = "XDG_DATA_DIRS",
 };
 
+#ifdef WIN32
+static const char *const xdg_defaults_env_vars[] = {
+  [kXDGConfigHome] = "LOCALAPPDATA",
+  [kXDGDataHome] = "LOCALAPPDATA",
+  [kXDGCacheHome] = "TEMP",
+  [kXDGRuntimeDir] = NULL,
+  [kXDGConfigDirs] = NULL,
+  [kXDGDataDirs] = NULL,
+};
+#endif
+
 /// Defaults for XDGVarType values
 ///
 /// Used in case environment variables contain nothing. Need to be expanded.
 static const char *const xdg_defaults[] = {
 #ifdef WIN32
-  // Windows
-  [kXDGConfigHome] = "$LOCALAPPDATA",
-  [kXDGDataHome]   = "$LOCALAPPDATA",
-  [kXDGCacheHome]  = "$TEMP",
+  [kXDGConfigHome] = "~\\AppData\\Local",
+  [kXDGDataHome] = "~\\AppData\\Local",
+  [kXDGCacheHome] = "~\\AppData\\Local\\Temp",
   [kXDGRuntimeDir] = NULL,
   [kXDGConfigDirs] = NULL,
   [kXDGDataDirs] = NULL,
 #else
-  // Linux, BSD, CYGWIN, Apple
   [kXDGConfigHome] = "~/.config",
   [kXDGDataHome] = "~/.local/share",
   [kXDGCacheHome] = "~/.cache",
@@ -50,7 +59,14 @@ char *stdpaths_get_xdg_var(const XDGVarType idx)
   const char *const env = xdg_env_vars[idx];
   const char *const fallback = xdg_defaults[idx];
 
-  const char *const env_val = os_getenv(env);
+  const char *env_val = os_getenv(env);
+
+#ifdef WIN32
+  if (env_val == NULL) {
+    env_val = os_getenv(xdg_defaults_env_vars[idx]);
+  }
+#endif
+
   char *ret = NULL;
   if (env_val != NULL) {
     ret = xstrdup(env_val);