Look for user nim.cfg in "nim/" subdir in usual config dir locations (#8662)

Fixes https://github.com/nim-lang/Nim/issues/8661.

changelog.md

@@ -230,4 +230,11 @@
 - On Posix systems the global system wide configuration is now put under ``/etc/nim/nim.cfg``,
   it used to be ``/etc/nim.cfg``. Usually it does not exist, however.
 
+- On Posix systems the user configuration is now looked under ``$XDG_CONFIG_HOME/nim/nim.cfg``
+  (if ``XDG_CONFIG_HOME`` is not defined, then under ``~/.config/nim/nim.cfg``). It used to be
+  ``$XDG_CONFIG_DIR/nim.cfg`` (and ``~/.config/nim.cfg``).
+
+  Similarly, on Windows, the user configuration is now looked under ``%APPDATA%/nim/nim.cfg``.
+  This used to be ``%APPDATA%/nim.cfg``.
+
 ### Bugfixes

compiler/nimconf.nim

@@ -220,7 +220,7 @@ proc readConfigFile(
     return true
 
 proc getUserConfigPath(filename: string): string =
-  result = joinPath(getConfigDir(), filename)
+  result = joinPath([getConfigDir(), "nim", filename])
 
 proc getSystemConfigPath(conf: ConfigRef; filename: string): string =
   # try standard configuration file (installation did not distribute files

lib/pure/ospaths.nim

@@ -525,14 +525,14 @@ proc getConfigDir*(): string {.rtl, extern: "nos$1",
   ## Returns the config directory of the current user for applications.
   ##
   ## On non-Windows OSs, this proc conforms to the XDG Base Directory
-  ## spec. Thus, this proc returns the value of the XDG_CONFIG_DIR environment
+  ## spec. Thus, this proc returns the value of the XDG_CONFIG_HOME environment
   ## variable if it is set, and returns the default configuration directory,
   ## "~/.config/", otherwise.
   ##
   ## An OS-dependent trailing slash is always present at the end of the
   ## returned string; `\\` on Windows and `/` on all other OSs.
   when defined(windows): return string(getEnv("APPDATA")) & "\\"
-  elif getEnv("XDG_CONFIG_DIR"): return string(getEnv("XDG_CONFIG_DIR")) & "/"
+  elif getEnv("XDG_CONFIG_HOME"): return string(getEnv("XDG_CONFIG_HOME")) & "/"
   else: return string(getEnv("HOME")) & "/.config/"
 
 proc getTempDir*(): string {.rtl, extern: "nos$1",