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;;; fidl-mode.el - A major mode for editing fidl files.
;;; Copyright (c) 2022 The Fuchsia Authors. All rights reserved.
;;; Use of this source code is governed by a BSD-style license that can be
;;; found in the LICENSE file.
;; Author: Max Regan <>
;; Created: December 2, 2022
;; Keywords: tools, fuchsia, fidl
;; This file is not part of GNU Emacs.
;;; Commentary:
;; A major mode for editing FIDL files. FIDL stands for Fuchsia Interface
;; Definition Language, which is the specification for IPC messages in Fuchsia.
;; For more information on FIDL, see the Fuchsia documentation:
;; This source was adapted from gn-mode.el:
;;; Code:
(require 'smie)
(defgroup fidl nil
"Major mode for editing FIDL files."
:prefix "fidl-"
:group 'languages)
(defcustom fidl-indent-basic 4
"The number of spaces to indent a new scope."
:group 'fidl
:type 'integer)
(defgroup fidl-faces nil
"Faces used in FIDL mode."
:group 'fidl
:group 'faces)
(defvar fidl-font-lock-reserved-keywords
'("alias" "as" "bits" "compose" "const" "enum" "error" "flexible" "library"
"optional" "protocol" "reserved" "resource" "service" "struct" "strict"
"type" "union" "using" "table"))
(defvar fidl-font-lock-type-keywords
'("bool" "byte" "float32" "float64" "int8" "int16" "int32" "int64" "uint8"
"uint16" "uint32" "uint64"))
(defvar fidl-font-lock-constant-keywords
'("true" "false"))
;; Currently, the syntax highlighting does little more than color keywords
(defconst fidl-font-lock-keywords
`((,(regexp-opt fidl-font-lock-reserved-keywords 'words) .
(,(regexp-opt fidl-font-lock-type-keywords 'words) .
(,(regexp-opt fidl-font-lock-constant-keywords 'words) .
;; Literal hexidecimal integers
("0x[0-9A-Fa-f]+" . font-lock-constant-face)
;; Literal binary representation
("0b[01]*" . font-lock-constant-face)
;; Floating-point literals
("[-+]?[0-9]*\\.?" . font-lock-constant-face)
;; These SMIE rules are like those from the example in the docs, with tweaks to
;; the 'basic' element so they only trigger additional indent if they are
;; hanging, e.g. instead of:
;; Foo() -> ( resource struct {
;; bar
;; })
;; get:
;; Foo() -> ( resource struct {
;; bar
;; })
(defun fidl-smie-rules (method arg)
"This method is passed to `smie-setup' to handle FIDL's indentation rules.
METHOD and ARG are documented in smie."
(pcase (cons method arg)
;; See comment above
(`(:elem . basic) (if (smie-rule-hanging-p) fidl-indent-basic 0))
;; Treat items between ; as list elements
(`(,_ . ";") (smie-rule-separator method))
;; Don't indent 'list' elements after the first
(`(:list-intro . "") t)
;; See docs, needed for virtual indentation.
(`(:before . ,(or `"[" `"(" `"{")) (smie-rule-parent))))
(defun fuchsia-fill-paragraph (&optional justify)
"We only fill inside of comments in FIDL mode."
(interactive "P")
(or (fill-comment-paragraph justify)
;; Never return nil; `fill-paragraph' will perform its default behavior
;; if we do.
(define-derived-mode fidl-mode prog-mode "FIDL"
"Major mode for editing FIDL (Fuchsia Interface Definition Language)."
:group 'fidl
(setq-local comment-use-syntax t)
(setq-local comment-start "//")
(setq-local comment-end "")
;; Teach emacs fidl-mode about C-style double-slash comments
(modify-syntax-entry ?/ "< 12" fidl-mode-syntax-table)
(modify-syntax-entry ?\n "> " fidl-mode-syntax-table)
;; 80 characters for comments, per
(setq-local fill-column 80)
(setq-local fill-paragraph-function 'fuchsia-fill-paragraph)
(setq-local font-lock-defaults '(fidl-font-lock-keywords))
(setq-local indent-tabs-mode nil)
(smie-setup nil #'fidl-smie-rules)
(setq-local smie-indent-basic fidl-indent-basic))
(add-to-list 'auto-mode-alist '("\\.fidl\\'" . fidl-mode))
(provide 'fidl-mode)