lang/python: rewrite modeline version segment

+ Add $PYENV_ROOT/shims was added to exec-path, so pyenv python version
  is picked up on.
+ Fixes out-of-date python version in the modeline of other buffers
  after switching pyenv/pyvenv/conda envs.
+ The pipenv version and regular python display have been merged.

modules/lang/python/autoload/python.el

@@ -1,11 +1,18 @@
 ;;; lang/python/autoload/python.el -*- lexical-binding: t; -*-
 
+(defvar +python-version-cache (make-hash-table :test 'equal)
+  "TODO")
+
 ;;;###autoload
 (defun +python/repl ()
   "Open the Python REPL."
   (interactive)
   (process-buffer (run-python nil t t)))
 
+(defun +python--extract-version (prefix str)
+  (when str
+    (format "%s%s" prefix (cadr (split-string str " ")))))
+
 ;;;###autoload
 (defun +python-version ()
   "Return the currently installed version of python on your system or active in
@@ -14,18 +21,37 @@ the current pipenv.
 This is not necessarily aware of env management tools like virtualenv, pyenv or
 pipenv, unless those tools have modified the PATH that Emacs picked up when you
 started it."
-  (let* ((pipenv-dir (pipenv-project-p))
-         (default-directory (or pipenv-dir default-directory))
-         (command (if pipenv-dir
-                      "pipenv run python --version"
-                    "python --version"))
-         (bin (car (split-string command " "))))
-    (unless (executable-find bin)
-      (user-error "Couldn't find %s executable in PATH" bin))
-    (with-temp-buffer
-      (let ((p (apply #'call-process bin nil (current-buffer) nil
-                      (cdr (split-string command " " t))))
-            (output (string-trim (buffer-string))))
-        (unless (zerop p)
-          (user-error "'%s' failed: %s" command output))
-        (cadr (split-string output " " t))))))
+  (condition-case _
+      (if-let* ((proot (and (fboundp 'pipenv-project-p)
+                            (pipenv-project-p))))
+          (let* ((default-directory proot)
+                 (v (car (process-lines "pipenv" "run" "python" "--version"))))
+            (puthash proot
+                     (+python--extract-version "Pipenv " v)
+                     +python-version-cache))
+        (puthash (doom-project-root)
+                 (+python--extract-version "Python " (car (process-lines "python" "--version")))
+                 +python-version-cache))
+    (error "Python")))
+
+
+;;
+;; Hooks
+
+;;;###autoload
+(defun +python|update-version (&rest _)
+  "Update `+python--version' by consulting `+python-version' function."
+  (setq +python--version
+        (or (gethash (or (and (fboundp 'pipenv-project-p)
+                              (pipenv-project-p))
+                         (doom-project-root))
+                     +python-version-cache)
+            (+python-version))))
+
+;;;###autoload
+(defun +python|update-version-in-all-buffers ()
+  "Update `+python-version' in all buffers in `python-mode'."
+  (dolist (buffer (doom-buffers-in-mode 'python-mode))
+    (setq +python-version-cache (clrhash +python-version-cache))
+    (with-current-buffer buffer
+      (+python|update-version))))