ruby-ts-mode: Highlight builtin methods

* lisp/progmodes/ruby-mode.el (ruby-builtin-methods-with-reqs)
(ruby-builtin-methods-no-reqs): New constants, extracted.
(ruby-font-lock-keywords): Replace values with references.

* lisp/progmodes/ruby-ts-mode.el (ruby-ts--builtin-methods): New
variable.  Construct regexp from aforementioned constants' values.

* lisp/progmodes/ruby-ts-mode.el (ruby-ts--font-lock-settings):
Use it.

* lisp/progmodes/ruby-ts-mode.el (ruby-ts-mode):
Add new font-lock feature: builtin-functions.

* lisp/progmodes/ruby-ts-mode.el (ruby-ts--predefined-constants)
(ruby-ts--predefined-variables): Unrelated to the rest of the
patch, add string-start and string-end anchors.

lisp/progmodes/ruby-mode.el

@@ -141,6 +141,81 @@ This should only be called after matching against `ruby-here-doc-beg-re'."
 
 It should match the part after \"def\" and until \"=\".")
 
+(defconst ruby-builtin-methods-with-reqs
+  '( ;; built-in methods on Kernel
+    "at_exit"
+    "autoload"
+    "autoload?"
+    "callcc"
+    "catch"
+    "eval"
+    "exec"
+    "format"
+    "lambda"
+    "load"
+    "loop"
+    "open"
+    "p"
+    "printf"
+    "proc"
+    "putc"
+    "require"
+    "require_relative"
+    "spawn"
+    "sprintf"
+    "syscall"
+    "system"
+    "throw"
+    "trace_var"
+    "trap"
+    "untrace_var"
+    "warn"
+    ;; keyword-like private methods on Module
+    "alias_method"
+    "attr"
+    "attr_accessor"
+    "attr_reader"
+    "attr_writer"
+    "define_method"
+    "extend"
+    "include"
+    "module_function"
+    "prepend"
+    "private_class_method"
+    "private_constant"
+    "public_class_method"
+    "public_constant"
+    "refine"
+    "using")
+  "List of built-in methods that require at least one argument.")
+
+(defconst ruby-builtin-methods-no-reqs
+  '("__callee__"
+    "__dir__"
+    "__method__"
+    "abort"
+    "binding"
+    "block_given?"
+    "caller"
+    "exit"
+    "exit!"
+    "fail"
+    "fork"
+    "global_variables"
+    "local_variables"
+    "print"
+    "private"
+    "protected"
+    "public"
+    "puts"
+    "raise"
+    "rand"
+    "readline"
+    "readlines"
+    "sleep"
+    "srand")
+  "List of built-in methods that only have optional arguments.")
+
 (defvar ruby-use-smie t)
 (make-obsolete-variable 'ruby-use-smie nil "28.1")
 
@@ -2292,84 +2367,13 @@ It will be properly highlighted even when the call omits parens.")
     ;; Core methods that have required arguments.
     (,(concat
        ruby-font-lock-keyword-beg-re
-       (regexp-opt
-        '( ;; built-in methods on Kernel
-          "at_exit"
-          "autoload"
-          "autoload?"
-          "callcc"
-          "catch"
-          "eval"
-          "exec"
-          "format"
-          "lambda"
-          "load"
-          "loop"
-          "open"
-          "p"
-          "printf"
-          "proc"
-          "putc"
-          "require"
-          "require_relative"
-          "spawn"
-          "sprintf"
-          "syscall"
-          "system"
-          "throw"
-          "trace_var"
-          "trap"
-          "untrace_var"
-          "warn"
-          ;; keyword-like private methods on Module
-          "alias_method"
-          "attr"
-          "attr_accessor"
-          "attr_reader"
-          "attr_writer"
-          "define_method"
-          "extend"
-          "include"
-          "module_function"
-          "prepend"
-          "private_class_method"
-          "private_constant"
-          "public_class_method"
-          "public_constant"
-          "refine"
-          "using")
-        'symbols))
+       (regexp-opt ruby-builtin-methods-with-reqs 'symbols))
      (1 (unless (looking-at " *\\(?:[]|,.)}=]\\|$\\)")
           font-lock-builtin-face)))
     ;; Kernel methods that have no required arguments.
     (,(concat
        ruby-font-lock-keyword-beg-re
-       (regexp-opt
-        '("__callee__"
-          "__dir__"
-          "__method__"
-          "abort"
-          "binding"
-          "block_given?"
-          "caller"
-          "exit"
-          "exit!"
-          "fail"
-          "fork"
-          "global_variables"
-          "local_variables"
-          "print"
-          "private"
-          "protected"
-          "public"
-          "puts"
-          "raise"
-          "rand"
-          "readline"
-          "readlines"
-          "sleep"
-          "srand")
-        'symbols))
+       (regexp-opt ruby-builtin-methods-no-reqs 'symbols))
      (1 font-lock-builtin-face))
     ;; Here-doc beginnings.
     (,ruby-here-doc-beg-re

lisp/progmodes/ruby-ts-mode.el

@@ -116,21 +116,30 @@
   "Ruby's punctuation characters.")
 
 (defvar ruby-ts--predefined-constants
-  (rx (or "ARGF" "ARGV" "DATA" "ENV" "RUBY_COPYRIGHT"
+  (rx string-start
+      (or "ARGF" "ARGV" "DATA" "ENV" "RUBY_COPYRIGHT"
           "RUBY_DESCRIPTION" "RUBY_ENGINE" "RUBY_ENGINE_VERSION"
           "RUBY_PATCHLEVEL" "RUBY_PLATFORM" "RUBY_RELEASE_DATE"
           "RUBY_REVISION" "RUBY_VERSION" "STDERR" "STDIN" "STDOUT"
-          "TOPLEVEL_BINDING"))
+          "TOPLEVEL_BINDING")
+      string-end)
   "Ruby predefined global constants.")
 
 (defvar ruby-ts--predefined-variables
-  (rx (or "$!" "$@" "$~" "$&" "$‘" "$‘" "$+" "$=" "$/" "$\\" "$," "$;"
+  (rx string-start
+      (or "$!" "$@" "$~" "$&" "$‘" "$‘" "$+" "$=" "$/" "$\\" "$," "$;"
           "$." "$<" "$>" "$_" "$*" "$$" "$?" "$:" "$LOAD_PATH"
           "$LOADED_FEATURES" "$DEBUG" "$FILENAME" "$stderr" "$stdin"
           "$stdout" "$VERBOSE" "$-a" "$-i" "$-l" "$-p"
-          (seq "$" (+ digit))))
+          (seq "$" (+ digit)))
+      string-end)
   "Ruby predefined global variables.")
 
+(defvar ruby-ts--builtin-methods
+  (format "\\`%s\\'" (regexp-opt (append ruby-builtin-methods-no-reqs
+                                         ruby-builtin-methods-with-reqs)))
+  "Ruby built-in methods.")
+
 (defconst ruby-ts--class-or-module-regex
   (rx string-start
       (or "class" "module" "singleton_class")
@@ -324,6 +333,12 @@ values of OVERRIDE"
      (in_clause
       pattern: (identifier) @font-lock-variable-name-face))
 
+   :language language
+   :feature 'builtin-functions
+   `((((identifier) @font-lock-builtin-face)
+      (:match ,ruby-ts--builtin-methods
+       @font-lock-builtin-face)))
+
    ;; Yuan recommends also putting method definitions into the
    ;; 'function' category (thus keeping it in both).  I've opted to
    ;; just use separate categories for them -- dgutov.
@@ -1022,9 +1037,9 @@ leading double colon is not added."
   (setq-local treesit-font-lock-feature-list
               '(( comment method-definition parameter-definition)
                 ( keyword regexp string type)
-                ( builtin-variable builtin-constant constant
+                ( builtin-variable builtin-constant builtin-functions
                   delimiter escape-sequence
-                  global instance
+                  constant global instance
                   interpolation literal symbol assignment)
                 ( bracket error function operator punctuation)))