[COMMITED] etc/poke-mode.el: add experimental SMIE-based indent

[Aurelien Aptel]

Got some help from Stephan Monier (SMIE author) to get something
started but this is still mostly gibberish to me.

Basic indentation is sort of working but sadly it often doesn't do
what one would expect...

2020-09-15  Aurélien Aptel  <aaptel@suse.com>

        * etc/poke-mode.el: Add SMIE grammar and indent code.
---
 ChangeLog        |  4 +++
 etc/poke-mode.el | 91 +++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 74 insertions(+), 21 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 28874b73..84790756 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2020-09-15  Aurélien Aptel  <aaptel@suse.com>
+
+       * etc/poke-mode.el: Add SMIE grammar and indent code.
+
 2020-09-15  Jose E. Marchesi  <jemarch@gnu.org>
 
        * pickles/time.pk: New file.
diff --git a/etc/poke-mode.el b/etc/poke-mode.el
index d8311611..253ee8ef 100644
--- a/etc/poke-mode.el
+++ b/etc/poke-mode.el
@@ -1,6 +1,8 @@
-;;; poke-mode.el --- Major mode for editing Poke programs
+;;; poke-mode.el --- Major mode for editing Poke programs  -*- 
lexical-binding: t; -*-
 
 ;; Copyright (C) 2020 Aurelien Aptel <aaptel@suse.com>
+;; SMIE grammar and help from Stefan Monnier <monnier@iro.umontreal.ca>
+;; Version: 0
 
 ;; Maintainer: Aurelien Aptel <aaptel@suse.com>
 
@@ -33,39 +35,35 @@
 
 ;;; Code:
 
+(require 'smie)
+
 (defgroup poke nil
   "Poke PK (pickle) editiong mode."
   :group 'languages)
 
 (defface poke-unit
   '((t (:inherit font-lock-constant-face)))
-  "Face used to highlight units (#unit)."
-  :group 'poke)
+  "Face used to highlight units (#unit).")
 
 (defface poke-attribute
   '((t (:inherit font-lock-builtin-face)))
-  "Face used to highlight attributes (var'attribute)."
-  :group 'poke)
+  "Face used to highlight attributes (var'attribute).")
 
 (defface poke-type
   '((t (:inherit font-lock-type-face)))
-  "Face used to highlight builtin types."
-  :group 'poke)
+  "Face used to highlight builtin types.")
 
 (defface poke-function
   '((t (:inherit font-lock-function-name-face)))
-  "Face used to highlight builtin functions."
-  :group 'poke)
+  "Face used to highlight builtin functions.")
 
 (defface poke-constant
   '((t (:inherit font-lock-constant-face)))
-  "Face used to highlight builtin constants."
-  :group 'poke)
+  "Face used to highlight builtin constants.")
 
 (defface poke-exception
   '((t (:inherit error)))
-  "Face used to highlight builtin exceptions."
-  :group 'poke)
+  "Face used to highlight builtin exceptions.")
 
 ;; from libpoke/pkl-lex.l
 (defconst poke-keywords
@@ -122,6 +120,7 @@
   "Keymap used in `poke-mode'.")
 
 (defvar poke-mode-syntax-table
+  ;; FIXME: Try and recognize <...> as parens, via `syntax-propertize'.
   (let ((st (make-syntax-table)))
     ;; symbol
     (modify-syntax-entry ?_  "_" st)
@@ -188,12 +187,58 @@
    `(,(rx symbol-start (regexp (regexp-opt poke-builtin-exceptions)) 
symbol-end)
      0 'poke-exception)))
 
+;;;; SMIE (indentation and navigation)
+
+(defcustom poke-indent-basic 2
+  "Basic indentation step."
+  :type 'integer)
+
+(defvar poke-smie-grammar
+  (smie-prec2->grammar
+   (smie-bnf->prec2
+    '((id)
+      (exp ("[" exps "]"))
+      (exps (exps "," exps) (exp))
+      (definition
+        (id "=" inst)
+        (id "=" id ":" inst))
+      (decl
+       ("defvar" definition)
+       ("method" definition)
+       ("deftype" definition)
+       (decl ";" decl))
+      (inst
+       (id)
+       ("struct" id)
+       ("union" id)
+       ))
+    '((assoc ";") (assoc ",")))))
+
+(defun poke--smie-forward-token ()
+  ;; FIXME:
+  ;; Don't merge ":" or ";" with some preceding punctuation such as ">".
+  (smie-default-forward-token))
+
+(defun poke--smie-backward-token ()
+  (forward-comment (- (point)))
+  (cond
+   ;; Don't merge ":" or ";" with some preceding punctuation such as ">".
+   ((memq (char-before) '(?: ?\;))
+    (forward-char -1)
+    (string (char-after)))
+   (t (smie-default-backward-token))))
+
+(defun poke-smie-rules (token kind)
+  (pcase (cons token kind)
+    (`(:elem . basic) poke-indent-basic)
+    ;; (`(:list-intro . "=") t)
+    ((and `(:before . "{") (guard (smie-rule-parent-p "struct")))
+     (smie-rule-parent 0))))
+
 ;;;###autoload (add-to-list 'auto-mode-alist '("\\.pk\\'" . poke-mode))
 ;;;###autoload
 (define-derived-mode poke-mode prog-mode "Poke"
-  "Major mode for editing Poke programs.
-
-\\{poke-mode-map}"
+  "Major mode for editing Poke programs."
 
   ;; for comment-region
   (setq-local comment-start "/*")
@@ -201,12 +246,16 @@
   (setq-local comment-end "*/")
   (setq-local comment-end-skip "[ \t]*\\*+/")
 
+  (smie-setup poke-smie-grammar #'poke-smie-rules
+              :forward-token #'poke--smie-forward-token
+              :backward-token #'poke--smie-backward-token)
+  
   ;; font-lock
-  (setq font-lock-defaults
-        '(poke-font-lock-keywords
-         nil ;; do string and comment font-lock from syntax table
-         nil ;; case-sensitive
-         nil)))
+  (setq-local font-lock-defaults
+              '(poke-font-lock-keywords
+               nil ;; do string and comment font-lock from syntax table
+               nil ;; case-sensitive
+               nil)))
 
 (provide 'poke-mode)
 ;;; poke-mode.el ends here
-- 
2.28.0