From 9f2ab28d4c9b044de707acbfb0d5f4558f378738 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miha=20Rihtar=C5=A1i=C4=8D?= <miha@kamnitnik.top>
Date: Mon, 15 Nov 2021 23:21:03 +0100
Subject: [PATCH 4/5] Highlight non-existent commands in M-x shell

* lisp/shell.el (shell-mode): Enable highlighting of non-existent
commands if requested.
(shell-highlight-undef-aliases):
(shell-highlight-undef-remote-file-name-inhibit-cache): New user
options.
(shell-highlight-undef-mode): New minor mode.
(shell-highlight-undef-defined-face):
(shell-highlight-undef-undefined-face):
(shell-highlight-undef-alias-face): New faces.
(shell-highlight-undef--exec-cache):
(shell-highlight-undef--face):
(shell-highlight-undef-keywords):
(shell-highlight-undef-regexp):
(shell-highlight-undef--executable-find):
(shell-highlight-undef-matcher):
(shell-highlight-undef--indirect):
(shell-highlight--setup):
(shell-highlight-undef-reset-mode): New functions and buffer local
variables.
---
 lisp/shell.el | 227 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 224 insertions(+), 3 deletions(-)

diff --git a/lisp/shell.el b/lisp/shell.el
index 347b3e04b9..3c008ec508 100644
--- a/lisp/shell.el
+++ b/lisp/shell.el
@@ -322,6 +322,16 @@ shell-comint-fl-mode-setup-hook
   :safe 'booleanp
   :version "29.1")
 
+(defcustom shell-highlight-undef-enable nil
+  "Enable highlighting of undefined commands in shell buffers.
+This variable only has effect when the shell is started.  Use the
+command `shell-highlight-undef-mode' to toggle highlighting of
+undefined commands."
+  :type 'boolean
+  :group 'shell
+  :safe 'booleanp
+  :version "29.1")
+
 (defvar shell-dirstack nil
   "List of directories saved by pushd in this buffer's shell.
 Thus, this does not include the shell's current directory.")
@@ -591,9 +601,11 @@ shell-mode
 buffer."
   :interactive nil
   :after-hook
-  (and (null comint-use-prompt-regexp)
-       shell-comint-fl-enable
-       (comint-fl-mode))
+  (unless comint-use-prompt-regexp
+    (if shell-comint-fl-enable
+        (comint-fl-mode))
+    (if shell-highlight-undef-enable
+        (shell-highlight-undef-mode)))
 
   (setq comint-prompt-regexp shell-prompt-pattern)
   (shell-completion-vars)
@@ -1471,6 +1483,215 @@ shell-narrow-to-prompt
            (point-max)
          (shell--prompt-begin-position))))))
 
+;;; Highlight undefined commands
+;;
+;; To highlight non-existent commands, customize
+;; `shell-highlight-undef-enable' to t.  To highlight some commands as
+;; aliases, add them to `shell-highlight-undef-aliases'.
+
+(defcustom shell-highlight-undef-aliases nil
+  "List commands to highlight as a command alias."
+  :group 'shell
+  :type '(repeat string)
+  :version "29.1")
+
+(defface shell-highlight-undef-defined-face
+  '((t :inherit 'font-lock-function-name-face))
+  "Face used for existent commands."
+  :group 'shell
+  :version "29.1")
+
+(defface shell-highlight-undef-undefined-face
+  '((t :inherit 'font-lock-warning-face))
+  "Face used for non-existent commands."
+  :group 'shell
+  :version "29.1")
+
+(defface shell-highlight-undef-alias-face
+  '((t :inherit 'font-lock-variable-name-face))
+  "Face used command aliases."
+  :group 'shell
+  :version "29.1")
+
+(defcustom shell-highlight-undef-remote-file-name-inhibit-cache nil
+  "Whether to use cache for finding remote executables.
+See `remote-file-name-inhibit-cache' for description."
+  :group 'faces
+  :type '(choice
+          (const :tag "Do not inhibit file name cache" nil)
+          (const :tag "Do not use file name cache" t)
+          (integer :tag "Do not use file name cache"
+                   :format "Do not use file name cache older than %v seconds"
+                   :value 10))
+  :version "29.1")
+
+(defvar shell--highlight-undef-exec-cache nil
+  "Cache of executable files found in `exec-path'.
+An alist, whose elements are of the form
+\(REMOTE TIME EXECUTABLES), where REMOTE is a string, returned by
+`file-remote-p', TIME is the return value of `float-time' end
+EXECUTABLES is a hash table with keys being the base-names of
+executable files.
+
+Cache expiry is controlled by the user option
+`remote-file-name-inhibit-cache'.")
+
+(defvar shell--highlight-undef-face 'shell-highlight-undef-defined-face)
+
+(defvar shell-highlight-undef-keywords
+  `((,#'shell-highlight-undef-matcher 6 shell--highlight-undef-face)))
+
+(defvar-local shell-highlight-undef-regexp regexp-unmatchable)
+
+(defun shell--highlight-undef-executable-find (command)
+  "Return non-nil if COMMAND is found in `exec-path'.
+Similar to `executable-find', but use cache stored in
+`shell--highlight-undef-exec-cache'."
+  (let ((remote (file-remote-p default-directory))
+        as ret found-in-cache delta-time)
+    (if (null remote)
+        (executable-find command)
+
+      (setq delta-time
+            shell-highlight-undef-remote-file-name-inhibit-cache)
+
+      (pcase (setq as (assoc remote shell--highlight-undef-exec-cache))
+        (`(,_ ,time ,hash)
+         (when (pcase delta-time
+                 ((pred numberp) (<= (float-time) (+ time delta-time)))
+                 ('t nil)
+                 ('nil t))
+           (setq ret (gethash command hash))
+           (setq found-in-cache t)))
+        (_ (setq as (list remote 0 (make-hash-table :test #'equal)))
+           (push as shell--highlight-undef-exec-cache)))
+
+      (if found-in-cache
+          ret
+        ;; Build cache
+        (setcar (cdr as) (float-time))
+        (let ((hash (clrhash (caddr as))))
+          (dolist (dir (exec-path))
+            (pcase-dolist (`(,f . ,attr)
+                           (condition-case nil
+                               (directory-files-and-attributes
+                                (concat remote dir) nil nil 'nosort 'integer)
+                             (file-error nil)))
+              ;; Approximation.  Assume every non-directory file in $PATH is an
+              ;; executable.  Alternatively, we could check
+              ;; `file-executable-p', but doing so for every file in $PATH is
+              ;; slow on remote machines.
+              (unless (eq t (file-attribute-type attr))
+                (puthash f t hash))))
+          (gethash command hash))))))
+
+(defun shell-highlight-undef-matcher (end)
+  "Matcher used to highlight commands up to END."
+  (when (re-search-forward shell-highlight-undef-regexp end t)
+    (save-match-data
+      (let ((cmd (match-string 6))
+            (beg (match-beginning 6)))
+        (setq shell--highlight-undef-face
+              (let* ((buf (buffer-base-buffer))
+                     (default-directory
+                      (if buf (buffer-local-value 'default-directory buf)
+                        default-directory)))
+                (cond
+                 ;; Don't highlight command output.  Mostly useful if
+                 ;; `shell-comint-fl-mode' is disabled.
+                 ((text-property-any beg (point) 'field 'output)
+                  nil)
+                 ((member cmd shell-highlight-undef-aliases)
+                  'shell-highlight-undef-alias-face)
+                 ;; Check if it contains a directory separator
+                 ((file-name-directory cmd)
+                  (when (file-name-absolute-p cmd)
+                    (setq cmd (concat
+                               (or (bound-and-true-p comint-file-name-prefix)
+                                   (file-remote-p default-directory))
+                               cmd)))
+                  (if (or (file-executable-p cmd)
+                          (file-directory-p cmd))
+                      'shell-highlight-undef-defined-face
+                    'shell-highlight-undef-undefined-face))
+                 ((shell--highlight-undef-executable-find cmd)
+                  'shell-highlight-undef-defined-face)
+                 (t 'shell-highlight-undef-undefined-face))))))
+    t))
+
+(defvar-local shell--highlight-undef-indirect nil
+  "Whether we are using `shell-comint-fl-mode' indirect buffer.")
+
+(declare-function sh-feature "sh-script" (alist &optional function))
+(defvar sh-leading-keywords)
+(defvar sh-other-keywords)
+
+(define-minor-mode shell-highlight-undef-mode
+  "Highlight undefined shell commands and aliases."
+  :init-value nil
+  (if shell--highlight-undef-indirect
+      (progn
+        (setq shell--highlight-undef-indirect nil)
+        (when-let ((buf (comint-indirect-buffer t)))
+          (with-current-buffer buf
+            (font-lock-remove-keywords nil shell-highlight-undef-keywords))))
+    (font-lock-remove-keywords nil shell-highlight-undef-keywords))
+  (remove-hook 'comint-fl-mode-hook
+               #'shell-highlight-undef-reset-mode t)
+  (remove-hook 'comint-indirect-setup-hook #'shell--highlight-undef-setup t)
+
+  (when shell-highlight-undef-mode
+    (when comint-use-prompt-regexp
+      (setq shell-highlight-undef-mode nil)
+      (error
+       "`shell-highlight-undef-mode' is incompatible with `comint-use-prompt-regexp'"))
+
+    (require 'sh-script)
+
+    (let ((regexp
+           ;; Adapted from `sh-font-lock-keywords-1'
+           (concat
+            "\\("
+            "[;(){}`|&]"
+            (if comint-fl-mode
+                ;; `comint-fl-mode' already puts point-min on end of
+                ;; prompt
+                ""
+              (concat "\\|" comint-prompt-regexp))
+            "\\|^"
+            "\\)"
+            "[ \t]*\\(\\("
+            (regexp-opt (sh-feature sh-leading-keywords) t)
+            "[ \t]+\\)?"
+            (regexp-opt (append (sh-feature sh-leading-keywords)
+                                (sh-feature sh-other-keywords))
+                        t)
+            "[ \t]+\\)?\\_<\\(\\(?:\\s_\\|\\sw\\|/\\)+\\)\\_>")))
+      (cond (comint-fl-mode
+             (setq shell--highlight-undef-indirect t)
+             (if-let ((buf (comint-indirect-buffer t)))
+                 (with-current-buffer buf
+                   (shell--highlight-undef-setup regexp))
+               (add-hook 'comint-indirect-setup-hook
+                         (lambda ()
+                           (shell--highlight-undef-setup regexp))
+                         nil t)))
+            (t (shell--highlight-undef-setup regexp))))
+
+    (add-hook 'comint-fl-mode-hook
+              #'shell-highlight-undef-reset-mode nil t))
+
+  (font-lock-flush))
+
+(defun shell--highlight-undef-setup (regexp)
+  (font-lock-add-keywords nil shell-highlight-undef-keywords t)
+  (setq shell-highlight-undef-regexp regexp))
+
+(defun shell-highlight-undef-reset-mode ()
+  "If `shell-highlight-undef-mode' is on, turn it off and on."
+  (when shell-highlight-undef-mode
+    (shell-highlight-undef-mode 1)))
+
 (provide 'shell)
 
 ;;; shell.el ends here
-- 
2.34.0