From c4eac600dffc7cfd04e260059cb40757f46fa8a0 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 23:13:03 +0100
Subject: [PATCH 2/5] Input fontification for M-x shell

* lisp/shell.el (shell-comint-fl-enable): New user option to control
input fontification.
(shell-indirect-setup-hook): New hook.
(shell-mode): Set up and enable input fontification.
---
 lisp/shell.el | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/lisp/shell.el b/lisp/shell.el
index 370532ea46..a91a59f070 100644
--- a/lisp/shell.el
+++ b/lisp/shell.el
@@ -306,6 +306,22 @@ shell-input-autoexpand
 		 (const :tag "on" t))
   :group 'shell)
 
+(defcustom shell-comint-fl-enable t
+  "Enable highlighting of input in shell buffers.
+This variable only has effect when the shell is started.  Use the
+command `comint-fl-mode' to toggle highlighting of input."
+  :type 'boolean
+  :group 'shell
+  :safe 'booleanp
+  :version "29.1")
+
+(defcustom shell-indirect-setup-hook nil
+  "Hook run after setting up an indirect shell fontification buffer."
+  :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.")
@@ -516,6 +532,8 @@ shell-completion-vars
 
 (put 'shell-mode 'mode-class 'special)
 
+(defvar sh-shell-file)
+
 (define-derived-mode shell-mode comint-mode "Shell"
   "Major mode for interacting with an inferior shell.
 \\<shell-mode-map>
@@ -572,6 +590,11 @@ shell-mode
 control whether input and output cause the window to scroll to the end of the
 buffer."
   :interactive nil
+  :after-hook
+  (and (null comint-use-prompt-regexp)
+       shell-comint-fl-enable
+       (comint-fl-mode))
+
   (setq comint-prompt-regexp shell-prompt-pattern)
   (shell-completion-vars)
   (setq-local paragraph-separate "\\'")
@@ -591,6 +614,19 @@ shell-mode
   (setq-local ansi-color-apply-face-function #'shell-apply-ansi-color)
   (shell-reapply-ansi-color)
 
+  (add-hook 'comint-indirect-setup-hook
+            #'shell-indirect-setup-hook 'append t)
+  (setq comint-indirect-setup-function
+        (let ((shell shell--start-prog))
+          (lambda ()
+            (require 'sh-script)
+            (cl-letf
+                (((default-value 'sh-shell-file)
+                  (or shell sh-shell-file))
+                 (inhibit-message t)
+                 (message-log-max nil))
+              (sh-mode)))))
+
   ;; This is not really correct, since the shell buffer does not really
   ;; edit this directory.  But it is useful in the buffer list and menus.
   (setq list-buffers-directory (expand-file-name default-directory))
@@ -645,6 +681,10 @@ shell-mode
                     ": [[:digit:]]+:[[:digit:]]+;")))
     (comint-read-input-ring t)))
 
+(defun shell-indirect-setup-hook ()
+  "Run `shell-indirect-setup-hook'."
+  (run-hooks 'shell-indirect-setup-hook))
+
 (defun shell-apply-ansi-color (beg end face)
   "Apply FACE as the ansi-color face for the text between BEG and END."
   (when face
-- 
2.34.0