Breadcrumb: first stab, very slow

* lisp/progmodes/breadcrumb.el: New file

lisp/progmodes/breadcrumb.el

@@ -0,0 +1,93 @@
+;;; breadcrumb.el --- imenu-based breadcrumb paths   -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2023  João Távora
+
+;; Author: João Távora <joaotavora@gmail.com>
+;; Keywords:
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+(require 'cl-lib)
+(require 'imenu)
+
+(defun bc-path (index-alist pos)
+  "Get breadcrumb for position POS given INDEX-ALIST."
+  (cl-labels ((containsp (node pos)
+                (let ((reg (get-text-property 0 'breadcrumb-region (car node)))
+                      bare-start)
+                  (cond (reg (<= (car reg) pos (cdr reg)))
+                        ((number-or-marker-p (setq bare-start (cdr node)))
+                         (save-excursion
+                           (goto-char bare-start)
+                           (end-of-defun)
+                           (<= bare-start pos (point)))))))
+              (dfs (node &optional path)
+                (or (and (consp (cdr node))
+                         (cl-loop with path = (cons (car node) path)
+                                  for c in (cdr node)
+                                  thereis (dfs c path)))
+                    (and (containsp node pos)
+                         (cons (car node) path)))))
+    (nreverse
+     (cl-loop for c in index-alist thereis (dfs c)))))
+
+(defvar bc--last-update-tick 0)
+
+(defvar bc--header-line-key [header-line mouse-1])
+
+(defun bc--format-node (p)
+  (let ((reg (get-text-property 0 'breadcrumb-region p)))
+    (if reg
+        (propertize p
+                    'mouse-face 'header-line-highlight
+                    'help-echo "Go here"
+                    'keymap (let ((m (make-sparse-keymap)))
+                              (define-key m bc--header-line-key
+                                          (lambda (&rest _e)
+                                            (interactive)
+                                            (push-mark)
+                                            (goto-char (car reg))))
+                              m))
+      p)))
+
+(defun bc-path-for-header-line ()
+  (cl-loop with alist =
+           (if (and imenu--index-alist
+                    (= (buffer-chars-modified-tick) bc--last-update-tick))
+               imenu--index-alist
+             (setq bc--last-update-tick (buffer-chars-modified-tick))
+             (imenu--make-index-alist))
+           for (p . more) on (bc-path alist (point))
+           collect (bc--format-node p) when more collect " > "))
+
+(defvar bc-header-line-format
+  '(:eval (bc-path-for-header-line)))
+
+(define-minor-mode bc-mode
+  "Header lines with breadcrumbs."
+  :init-value nil
+  (if bc-mode (add-to-list 'header-line-format bc-header-line-format)
+    (setq header-line-format (delq bc-header-line-format header-line-format))))
+
+(provide 'breadcrumb)
+;;; breadcrumb.el ends here
+
+;; Local Variables:
+;; read-symbol-shorthands: (("bc-" . "breadcrumb-"))
+;; End: