lang/sh: improve fontification for sh-mode

+ Fontify variables in double quotes (better)
+ Fontify command substitution in double quotes
+ Fontify built-in/common commands (see `+sh-builtin-keywords`)

modules/lang/sh/autoload.el

@@ -1,41 +1,29 @@
 ;;; lang/sh/autoload.el -*- lexical-binding: t; -*-
 
-(defvar sh-extra-font-lock--keywords
-  `((+sh--match-var-in-double-quoted-string
-     (2 font-lock-variable-name-face prepend))
-    (,(concat
-       "\\<"
-       (regexp-opt '("sudo" "echo" "ls" "sleep" "tee" "cd" "cat" "service"))
-       "\\>")
-     (0 'font-lock-builtin-face))))
-
 ;;;###autoload
-(defun +sh--in-double-quoted-string-p ()
-  "Non-nil if point in inside a double-quoted string."
-  (eq (nth 3 (syntax-ppss)) ?\"))
-
-;;;###autoload
-(defun +sh--match-var-in-double-quoted-string (limit)
+(defun +sh--match-variables-in-quotes (limit)
   "Search for variables in double-quoted strings bounded by LIMIT."
-  (let (res)
-    (while
-        (and (setq res
-                   (re-search-forward
-                    "\\$\\({#?\\)?\\([[:alpha:]_][[:alnum:]_]*\\|[-#?@!]\\)"
-                    limit t))
-             (not (+sh--in-double-quoted-string-p))))
-    res))
+  (with-syntax-table sh-mode-syntax-table
+    (let (res)
+      (while
+          (and (setq res
+                     (re-search-forward
+                      "\\(\\$\\)\\({.+?}\\|\\<.+?\\>\\)"
+                      limit t))
+               (not (eq (nth 3 (syntax-ppss)) ?\"))))
+      res)))
 
 ;;;###autoload
-(defun +sh|extra-fontify ()
-  "Activate sh-extra-font-lock."
-  (interactive)
-  (font-lock-add-keywords nil sh-extra-font-lock--keywords)
-  (if (fboundp 'font-lock-flush)
-      (font-lock-flush)
-    (when font-lock-mode
-      (with-no-warnings
-        (font-lock-fontify-buffer)))))
+(defun +sh--match-command-subst-in-quotes (limit)
+  "Search for variables in double-quoted strings bounded by LIMIT."
+  (with-syntax-table sh-mode-syntax-table
+    (let (res)
+      (while
+          (and (setq res
+                     (re-search-forward "\\(\\$(.+?)\\|`.+?`\\)"
+                                        limit t))
+               (not (eq (nth 3 (syntax-ppss)) ?\"))))
+      res)))
 
 (defvar sh-shell-file)
 ;;;###autoload

modules/lang/sh/config.el

@@ -1,15 +1,38 @@
 ;;; lang/sh/config.el -*- lexical-binding: t; -*-
 
+(defvar +sh-builtin-keywords
+  '("sudo" "echo" "ls" "sleep" "tee" "cd" "cat")
+  "A list of common shell commands and keywords to be fontified especially in
+`sh-mode'.")
+
+
+;;
+;; Plugins
+;;
+
 (def-package! sh-script ; built-in
   :mode ("\\.zsh$"   . sh-mode)
   :mode ("/bspwmrc$" . sh-mode)
   :init
-  (add-hook! sh-mode #'(flycheck-mode highlight-numbers-mode +sh|extra-fontify))
+  (add-hook! sh-mode #'(flycheck-mode highlight-numbers-mode))
   :config
   (set! :electric 'sh-mode :words '("else" "elif" "fi" "done" "then" "do" "esac" ";;"))
   (set! :repl 'sh-mode #'+sh/repl)
+
   (setq sh-indent-after-continuation 'always)
 
+  ;; 1. Fontifies variables in double quotes
+  ;; 2. Fontify command substitution in double quotes
+  ;; 3. Fontify built-in/common commands (see `+sh-builtin-keywords')
+  (font-lock-add-keywords
+   'sh-mode `((+sh--match-variables-in-quotes
+               (1 'default prepend)
+               (2 'font-lock-variable-name-face prepend))
+              (+sh--match-command-subst-in-quotes
+               (0 'sh-quoted-exec prepend))
+              (,(concat "^\\s-*" (regexp-opt +sh-builtin-keywords 'words))
+               (0 'font-lock-builtin-face t))))
+
   ;; sh-mode has file extensions checks for other shells, but not zsh, so...
   (defun +sh|detect-zsh ()
     (when (and buffer-file-name (string-match-p "\\.zsh\\'" buffer-file-name))