From cec4b8ac171686b53ff730c23d90ef25039e6791 Mon Sep 17 00:00:00 2001
From: Leo Liu <sdl.web@gmail.com>
Date: Fri, 7 Oct 2016 19:37:19 +0800
Subject: New commands to ease looking up OTP documentation

- erldoc-browse:        open the manual entry for an MFA in the browser
- erldoc-apropos:       list MFAs containing a substring
- erldoc-browse-topic:  open user guides in the browser
---
 lib/tools/emacs/Makefile        |   1 +
 lib/tools/emacs/erlang-start.el |  14 ++
 lib/tools/emacs/erlang.el       |   5 +
 lib/tools/emacs/erldoc.el       | 508 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 528 insertions(+)
 create mode 100644 lib/tools/emacs/erldoc.el

(limited to 'lib/tools')

diff --git a/lib/tools/emacs/Makefile b/lib/tools/emacs/Makefile
index e1b195ef97..35c93ba4ed 100644
--- a/lib/tools/emacs/Makefile
+++ b/lib/tools/emacs/Makefile
@@ -38,6 +38,7 @@ MAN_FILES= \
 	tags.3
 
 EMACS_FILES= \
+	erldoc \
 	erlang-skels \
 	erlang-skels-old \
 	erlang_appwiz \
diff --git a/lib/tools/emacs/erlang-start.el b/lib/tools/emacs/erlang-start.el
index f9a6d24b2c..160057e179 100644
--- a/lib/tools/emacs/erlang-start.el
+++ b/lib/tools/emacs/erlang-start.el
@@ -78,8 +78,22 @@
 (autoload 'erlang-find-tag-other-window "erlang"
   "Like `find-tag-other-window'.  Capable of retreiving Erlang modules.")
 
+;;
+;; Declare functions in "erlang-edoc.el".
+;;
+
 (autoload 'erlang-edoc-mode "erlang-edoc" "Toggle Erlang-Edoc mode on or off." t)
 
+;;
+;; Declare functions in "erldoc.el".
+;;
+
+(autoload 'erldoc-browse "erldoc" "\n\n(fn MFA)" t nil)
+(autoload 'erldoc-browse-topic "erldoc" "\n\n(fn TOPIC)" t nil)
+(autoload 'erldoc-apropos "erldoc" "\n\n(fn PATTERN)" t nil)
+(autoload 'erldoc-eldoc-function "erldoc" "\
+A function suitable for `eldoc-documentation-function'.\n\n(fn)" nil nil)
+
 ;;
 ;; Associate files extensions ".erl" and ".hrl" with Erlang mode.
 ;;
diff --git a/lib/tools/emacs/erlang.el b/lib/tools/emacs/erlang.el
index cc22903e7f..40f0bb7f80 100644
--- a/lib/tools/emacs/erlang.el
+++ b/lib/tools/emacs/erlang.el
@@ -1440,6 +1440,11 @@ Other commands:
   (erlang-skel-init)
   (when (fboundp 'tempo-use-tag-list)
     (tempo-use-tag-list 'erlang-tempo-tags))
+  (when (and (fboundp 'add-function) (fboundp 'erldoc-eldoc-function))
+    (or eldoc-documentation-function
+        (setq-local eldoc-documentation-function #'ignore))
+    (add-function :before-until (local 'eldoc-documentation-function)
+                  #'erldoc-eldoc-function))
   (run-hooks 'erlang-mode-hook)
   (if (zerop (buffer-size))
       (run-hooks 'erlang-new-file-hook)))
diff --git a/lib/tools/emacs/erldoc.el b/lib/tools/emacs/erldoc.el
new file mode 100644
index 0000000000..cb355374d9
--- /dev/null
+++ b/lib/tools/emacs/erldoc.el
@@ -0,0 +1,508 @@
+;;; erldoc.el --- browse Erlang/OTP documentation    -*- lexical-binding: t; -*-
+
+;; %CopyrightBegin%
+;;
+;; Copyright Ericsson AB 2016. All Rights Reserved.
+;;
+;; Licensed under the Apache License, Version 2.0 (the "License");
+;; you may not use this file except in compliance with the License.
+;; You may obtain a copy of the License at
+;;
+;;     http://www.apache.org/licenses/LICENSE-2.0
+;;
+;; Unless required by applicable law or agreed to in writing, software
+;; distributed under the License is distributed on an "AS IS" BASIS,
+;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;; See the License for the specific language governing permissions and
+;; limitations under the License.
+;;
+;; %CopyrightEnd%
+
+;;; Commentary:
+
+;; Crawl Erlang/OTP HTML documentation and generate lookup tables.
+;;
+;; This package depends on `cl-lib', `pcase' and
+;; `libxml-parse-html-region'; emacs 24+ compiled with libxml2 should
+;; work. On emacs 24.1 and 24.2 do `M-x package-install RET cl-lib
+;; RET' to install `cl-lib'.
+;;
+;; Please customise `erldoc-man-index' to point to your local OTP
+;; documentation.
+;;
+;; To use:
+;;
+;;   (define-key help-map "u" 'erldoc-browse)
+;;   (define-key help-map "t" 'erldoc-browse-topic)
+;;   (define-key help-map "a" 'erldoc-apropos)
+;;
+;; Note: these commands trigger indexing OTP documentation on first
+;; run with cache to disk which may take 1-2 minutes.
+
+
+;;; Examples:
+
+;; 1. `M-x erldoc-browse RET erlang:integer_to_binary/2 RET' opens the
+;;    `erlang' manual anchored on the entry for `integer_to_binary/2'.
+;;
+;; 2. `M-x erldoc-apropos RET first RET' list all MFAs matching
+;;    substring `first'.
+;;
+;; 3. `M-x erldoc-browse-topic RET efficiency_guide#Introduction RET'
+;;    opens chapter `Introduction' of the `Efficiency Guide' in the
+;;    browser.
+
+;;; History:
+
+;; Written in December 2013 as a temporary solution to help me browse
+;; the rich Erlang/OTP documentation. Three years on I find myself
+;; still using it every day.  - Leo (2016)
+
+;;; Code:
+
+(eval-when-compile (require 'url-parse))
+(require 'cl-lib)
+(require 'erlang)
+
+(eval-and-compile                       ;for emacs < 24.3
+  (or (fboundp 'user-error) (defalias 'user-error 'error)))
+
+(defgroup erldoc nil
+  "Browse Erlang document."
+  :group 'help)
+
+(defcustom erldoc-man-index "http://www.erlang.org/doc/man_index.html"
+  "The URL to the man_index.html page.
+Note it is advisable to customise this to a local URL for example
+`file:///usr/local/19.1/lib/erlang/doc/man_index.html' to speed
+up the indexing."
+  :type 'string
+  :group 'erldoc)
+
+(defcustom erldoc-verify-man-path nil
+  "If non-nil verify man path existence for `file://'."
+  :type 'boolean
+  :group 'erldoc)
+
+(defcustom erldoc-output-file (locate-user-emacs-file "cache/erldoc")
+  "File to store the parsed results."
+  :type 'file
+  :group 'erldoc)
+
+(defun erldoc-strip-string (s)
+  (let* ((re "[ \t\n\r\f\v\u00a0]+")
+         (from (if (string-match (concat "\\`" re) s) (match-end 0) 0))
+         (to (and (string-match (concat re "\\'") s) (match-beginning 0))))
+    (substring s from (and to (max to from)))))
+
+;; Note: don't know how to get the BASE-URL to
+;; `libxml-parse-html-region' to work.
+(defun erldoc-expand-url (url base-url)
+  (if (url-type (url-generic-parse-url url))
+      url
+    (let* ((base (url-generic-parse-url base-url))
+           (dir (directory-file-name (file-name-directory (url-filename base)))))
+      (setf (url-filename base) (expand-file-name url dir))
+      (url-recreate-url base))))
+
+(defun erldoc-parse-html (url)
+  (with-temp-buffer
+    (url-insert-file-contents url)
+    (libxml-parse-html-region (point-min) (point-max))))
+
+(defalias 'erldoc-dom-text-node-p #'stringp)
+
+(defun erldoc-dom-attributes (dom)
+  (and (not (erldoc-dom-text-node-p dom)) (cadr dom)))
+
+(defun erldoc-dom-get-attribute (dom attrib-name)
+  (cdr (assq attrib-name (erldoc-dom-attributes dom))))
+
+(defun erldoc-dom-children (dom)
+  (and (not (erldoc-dom-text-node-p dom)) (cddr dom)))
+
+(defun erldoc-dom-get-text (dom)
+  (let ((text (car (last (erldoc-dom-children dom)))))
+    (and (erldoc-dom-text-node-p text) text)))
+
+(defvar erldoc-dom-walk-parent nil)
+(defvar erldoc-dom-walk-siblings nil)
+
+(defun erldoc-dom-walk (dom k)
+  (funcall k dom)
+  (let ((erldoc-dom-walk-parent dom)
+        (erldoc-dom-walk-siblings (unless (erldoc-dom-text-node-p dom)
+                                    (cddr dom))))
+    (dolist (child erldoc-dom-walk-siblings)
+      (erldoc-dom-walk child k))))
+
+(defun erldoc-dom-get-element (dom element-name)
+  (catch 'return
+    (erldoc-dom-walk dom (lambda (d)
+                           (when (eq (car-safe d) element-name)
+                             (throw 'return d))))))
+
+(defun erldoc-dom-get-element-by-id (dom id)
+  (catch 'return
+    (erldoc-dom-walk dom (lambda (d)
+                           (when (equal (erldoc-dom-get-attribute d 'id) id)
+                             (throw 'return d))))))
+
+(defun erldoc-dom-get-elements-by-id (dom id)
+  (let (result)
+    (erldoc-dom-walk dom (lambda (d)
+                           (when (equal (erldoc-dom-get-attribute d 'id) id)
+                             (push d result))))
+    (nreverse result)))
+
+(defun erldoc-fix-path (url)
+  (if (and erldoc-verify-man-path
+           ;; Could only verify local files
+           (equal (url-type (url-generic-parse-url url)) "file"))
+      (let* ((obj (url-generic-parse-url url))
+             (new (car (file-expand-wildcards
+                        (replace-regexp-in-string
+                         "-[0-9]+\\(?:[.][0-9]+\\)*" "*"
+                         (url-filename obj))))))
+        (or new (error "File %s does not exist" (url-filename obj)))
+        (setf (url-filename obj) new)
+        (url-recreate-url obj))
+    url))
+
+(defun erldoc-parse-man-index (url)
+  (let ((table (erldoc-dom-get-element (erldoc-parse-html url) 'table))
+        (mans))
+    (erldoc-dom-walk
+     table
+     (lambda (d)
+       (when (eq (car-safe d) 'a)
+         (let ((href (erldoc-dom-get-attribute d 'href)))
+           (when (and href (not (string-match-p "index\\.html\\'" href)))
+             (with-demoted-errors "erldoc-parse-man-index: %S"
+               (push (cons (erldoc-dom-get-text d)
+                           (erldoc-fix-path (erldoc-expand-url href url)))
+                     mans)))))))
+    (nreverse mans)))
+
+(defun erldoc-parse-man (man)
+  (let ((dom (erldoc-parse-html (cdr man)))
+        (table (make-hash-table :test #'equal)))
+    (erldoc-dom-walk
+     (erldoc-dom-get-element-by-id dom "loadscrollpos")
+     (lambda (d)
+       (let ((href (erldoc-dom-get-attribute d 'href)))
+         (when (and href (string-match "#" href))
+           (puthash (substring href (match-end 0))
+                    (list (concat (car man) ":" (erldoc-strip-string
+                                                 (erldoc-dom-get-text d)))
+                          (erldoc-expand-url href (cdr man)))
+                    table)))))
+    (let ((span-content
+           (lambda (span)
+             (let ((texts))
+               (erldoc-dom-walk span
+                                (lambda (d)
+                                  (and (erldoc-dom-text-node-p d)
+                                       (push (erldoc-strip-string d) texts))))
+               (and texts (mapconcat 'identity (nreverse texts) " ")))))
+          entries)
+      (erldoc-dom-walk
+       dom
+       (lambda (d)
+         ;; Get the full function signature.
+         (when (and (eq (car-safe d) 'a)
+                    (gethash (erldoc-dom-get-attribute d 'name) table))
+           (push (append (gethash (erldoc-dom-get-attribute d 'name) table)
+                         (list (funcall span-content
+                                        (or (erldoc-dom-get-element d 'span)
+                                            (cadr (memq d erldoc-dom-walk-siblings))))))
+                 entries))
+         ;; Get data types
+         (when (and (eq (car-safe d) 'a)
+                    (string-prefix-p "type-"
+                                     (or (erldoc-dom-get-attribute d 'name) "")))
+           (push (list (concat (car man) ":" (funcall span-content d))
+                       (concat (cdr man) "#" (erldoc-dom-get-attribute d 'name))
+                       (funcall span-content erldoc-dom-walk-parent))
+                 entries))))
+      entries)))
+
+(defun erldoc-parse-all (man-index output &optional json)
+  (let* ((output (expand-file-name output))
+         (table (make-hash-table :size 11503 :test #'equal))
+         (mans (erldoc-parse-man-index man-index))
+         (progress 1)
+         (reporter (make-progress-reporter "Parsing Erlang/OTP documentation"
+                                           progress (length mans)))
+         fails all)
+    (dolist (man mans)
+      (condition-case err
+          (push (erldoc-parse-man man) all)
+        (error (push (error-message-string err) fails)))
+      (accept-process-output nil 0.01)
+      (progress-reporter-update reporter (cl-incf progress)))
+    (when fails
+      (display-warning 'erldoc-parse-all
+                       (format "\n\n%s" (mapconcat #'identity fails "\n"))
+                       :error))
+    (progress-reporter-done reporter)
+    (mapc (lambda (x) (puthash (car x) (cdr x) table))
+          (apply #'nconc (nreverse all)))
+    (with-temp-buffer
+      (if (not json)
+          (pp table (current-buffer))
+        (eval-and-compile (require 'json))
+        (let ((json-encoding-pretty-print t))
+          (insert (json-encode table))))
+      (unless (file-directory-p (file-name-directory output))
+        (make-directory (file-name-directory output) t))
+      (write-region nil nil output nil nil nil 'ask))))
+
+(defun erldoc-otp-release ()
+  "Get the otp release version (as string) or nil if not found."
+  (let ((otp (erldoc-dom-get-text
+              (erldoc-dom-get-element
+               (erldoc-parse-html
+                (erldoc-expand-url "index.html" erldoc-man-index))
+               'title))))
+    (and (string-match "[0-9.]+\\'" otp) (match-string 0 otp))))
+
+(defvar erldoc-browse-history nil)
+(defvar erldoc-lookup-table nil)
+
+(defun erldoc-lookup-table ()
+  (or erldoc-lookup-table
+      (progn
+        (unless (file-exists-p erldoc-output-file)
+          (let ((of (pcase (erldoc-otp-release)
+                      (`nil erldoc-output-file)
+                      (ver (concat erldoc-output-file "-" ver)))))
+            (unless (file-exists-p of)
+              (erldoc-parse-all erldoc-man-index of))
+            (unless (string= erldoc-output-file of)
+              (make-symbolic-link of erldoc-output-file))))
+        (setq erldoc-lookup-table
+              (with-temp-buffer
+                (insert-file-contents erldoc-output-file)
+                (read (current-buffer)))))))
+
+(defun erldoc-best-matches (mfa)
+  (pcase mfa
+    ((and `(,m ,f) (let a (erlang-get-function-arity)))
+     (let ((mfa (format "%s:%s/%s" m f a)))
+       (cond ((gethash mfa (erldoc-lookup-table)) (list mfa))
+             (m (all-completions (concat m ":" f "/") (erldoc-lookup-table)))
+             (t (let* ((mod (erlang-get-module))
+                       (mf1 (and mod (concat mod ":" f "/")))
+                       (mf2 (concat "erlang:" f "/"))
+                       (re (concat ":" (regexp-quote f) "/")))
+                  (or (and mf1 (all-completions mf1 (erldoc-lookup-table)))
+                      (all-completions mf2 (erldoc-lookup-table))
+                      (cl-loop for k being the hash-keys of (erldoc-lookup-table)
+                               when (string-match-p re k)
+                               collect k)))))))))
+
+;;;###autoload
+(defun erldoc-browse (mfa)
+  (interactive
+   (let ((default
+           ;; `erlang-mode-syntax-table' is lazily initialised.
+           (with-syntax-table (or erlang-mode-syntax-table (standard-syntax-table))
+             (ignore-errors
+               (erldoc-best-matches
+                (or (erlang-get-function-under-point)
+                    (save-excursion
+                      (goto-char (or (cadr (syntax-ppss)) (point)))
+                      (erlang-get-function-under-point))))))))
+     (list (completing-read (format (if default "Function {%d %s} (default %s): "
+                                      "Function: ")
+                                    (length default)
+                                    (if (= (length default) 1) "guess" "guesses")
+                                    (car default))
+                            (erldoc-lookup-table)
+                            nil t nil 'erldoc-browse-history default))))
+  (or (stringp mfa)
+      (signal 'wrong-type-argument (list 'string mfa 'mfa)))
+  (browse-url (or (car (gethash mfa (erldoc-lookup-table)))
+                  (user-error "No documentation for %s" mfa))))
+
+;;;###autoload
+(defun erldoc-apropos (pattern)
+  (interactive "sPattern: ")
+  (with-help-window (help-buffer)
+    (with-current-buffer standard-output
+      (princ (concat "Erldoc apropos pattern: " pattern "\n\n"))
+      (maphash (lambda (k v)
+                 (when (string-match-p pattern k)
+                   (insert-text-button k :type 'help-url
+                                       'help-args (list (car v)))
+                   (insert "\n")))
+               (erldoc-lookup-table)))))
+
+(defun erldoc-tokenize-signature (sig)
+  ;; Divide SIG into (MF ARGLIST RETTYPE)
+  (let ((from (if (string-match "\\`.+?(" sig)
+                  (1- (match-end 0))
+                0))
+        (to (and (string-match "\\s-*->\\s-*.*?\\'" sig) (match-beginning 0))))
+    (list (erldoc-strip-string (substring sig 0 from))
+          (erldoc-strip-string (substring sig from (and to (max from to))))
+          (and to (erldoc-strip-string (substring sig to))))))
+
+(defun erldoc-format-signature (mod fn)
+  (when (and mod fn (or erldoc-lookup-table
+                        (file-exists-p erldoc-output-file)))
+    (let ((re (concat "\\`" mod ":" fn "/\\([0-9]+\\)\\'"))
+          (sigs))
+      (maphash (lambda (k v)
+                 (when (string-match re k)
+                   (push (cons (string-to-number (match-string 1 k))
+                               (cdr (erldoc-tokenize-signature (cadr v))))
+                         sigs)))
+               (erldoc-lookup-table))
+      (when sigs
+        ;; Mostly single return type but there are exceptions such as
+        ;; `beam_lib:chunks/2,3'.
+        (let ((single-rettype
+               (cl-reduce (lambda (x1 x2) (and x1 x2 (equal x1 x2) x1))
+                          sigs :key #'cl-caddr))
+              (sigs (sort sigs #'car-less-than-car)))
+          (if single-rettype
+              (concat mod ":" fn (mapconcat #'cadr sigs " | ") " " single-rettype)
+            (mapconcat (lambda (x) (concat mod ":" fn (nth 1 x) " " (nth 2 x)))
+                       sigs "\n")))))))
+
+;;;###autoload
+(defun erldoc-eldoc-function ()
+  "A function suitable for `eldoc-documentation-function'."
+  (save-excursion
+    (pcase (erlang-get-function-under-point)
+      (`(,_ nil) )
+      (`(nil ,fn)  (erldoc-format-signature "erlang" fn))
+      (`(,mod ,fn) (erldoc-format-signature mod fn)))))
+
+(defun erldoc-parse-eeps-index ()
+  (let* ((url "http://www.erlang.org/eeps/")
+         (table (catch 'return
+                  (erldoc-dom-walk (erldoc-parse-html url)
+                                   (lambda (d)
+                                     (and (eq (car-safe d) 'table)
+                                          (equal (erldoc-dom-get-attribute d 'summary)
+                                                 "Numerical Index of EEPs")
+                                          (throw 'return d))))))
+         (fix-title (lambda (title)
+                      (replace-regexp-in-string
+                       "`` *" "" (replace-regexp-in-string " *``, *" " by " title))))
+         (result))
+    (erldoc-dom-walk
+     table (lambda (d)
+             (when (eq (car-safe d) 'a)
+               (push (cons (funcall fix-title (erldoc-dom-get-attribute d 'title))
+                           (erldoc-expand-url
+                            (erldoc-dom-get-attribute d 'href)
+                            url))
+                     result))))
+    (nreverse result)))
+
+(defvar erldoc-user-guides nil)
+
+(defvar erldoc-missing-user-guides
+  '("compiler" "hipe" "kernel" "os_mon" "parsetools" "typer")
+  "List of standard Erlang applications with no user guides.")
+
+;; Search in `code:lib_dir/0' using find LIB_DIR -type f -name
+;; '*_app.html'.
+(defvar erldoc-app-manuals '("crypto" "diameter" "erl_docgen"
+                             "kernel" "observer" "os_mon"
+                             "runtime_tools" "sasl" "snmp"
+                             "ssl" "test_server"
+                             ("ssh" . "SSH") ("stdlib" . "STDLIB")
+                             ("hipe" . "HiPE") ("typer" . "TypEr"))
+  "List of applications that come with a manual.")
+
+(defun erldoc-user-guide-chapters (user-guide)
+  (pcase-let ((`(,name . ,url) user-guide))
+    (unless (member name erldoc-missing-user-guides)
+      (let ((chaps (erldoc-dom-get-elements-by-id
+                    (erldoc-dom-get-element-by-id (erldoc-parse-html url) "leftnav")
+                    "no")))
+        (or chaps (warn "erldoc-user-guide-chapters no chapters found for `%s'"
+                        (cdr user-guide)))
+        (mapcar (lambda (li)
+                  (cons (concat name "#" (erldoc-dom-get-attribute li 'title))
+                        (erldoc-expand-url (erldoc-dom-get-attribute
+                                            (erldoc-dom-get-element li 'a) 'href)
+                                           url)))
+                chaps)))))
+
+(defun erldoc-user-guides-1 ()
+  (let ((url (erldoc-expand-url "applications.html" erldoc-man-index))
+        app-guides app-mans)
+    (erldoc-dom-walk
+     (erldoc-parse-html url)
+     (lambda (d)
+       (when (and (eq (car-safe d) 'a)
+                  (not (string-match-p "\\`[0-9.]+\\'" (erldoc-dom-get-text d))))
+         (with-demoted-errors "erldoc-user-guides-1: %S"
+           (let ((name (erldoc-strip-string (erldoc-dom-get-text d)))
+                 (index-page (erldoc-fix-path (erldoc-expand-url
+                                               (erldoc-dom-get-attribute d 'href) url))))
+             (push (cons name (if (member name erldoc-missing-user-guides)
+                                  index-page
+                                (erldoc-expand-url "users_guide.html" index-page)))
+                   app-guides)
+             ;; Collect application manuals.
+             (pcase (assoc name (mapcar (lambda (x) (if (consp x) x (cons x x)))
+                                        erldoc-app-manuals))
+               (`(,_ . ,manual)
+                (push (cons name
+                            (erldoc-expand-url (format "%s_app.html" manual)
+                                               index-page))
+                      app-mans))))))))
+    (list (nreverse app-guides)
+          (nreverse app-mans))))
+
+(defun erldoc-user-guides ()
+  (or erldoc-user-guides
+      (let ((file (concat erldoc-output-file "-topics")))
+        (unless (file-exists-p file)
+          (unless (file-directory-p (file-name-directory file))
+            (make-directory (file-name-directory file) t))
+          (with-temp-buffer
+            (pcase-let ((`(,guides ,mans) (erldoc-user-guides-1)))
+              (pp (append (cl-mapcan #'erldoc-user-guide-chapters
+                                     (append (mapcar
+                                              (lambda (dir)
+                                                (cons dir (erldoc-expand-url
+                                                           (concat dir "/users_guide.html")
+                                                           erldoc-man-index)))
+                                              '("design_principles"
+                                                "efficiency_guide"
+                                                "embedded"
+                                                "getting_started"
+                                                "installation_guide"
+                                                "oam"
+                                                "programming_examples"
+                                                "reference_manual"
+                                                "system_architecture_intro"
+                                                "system_principles"
+                                                "tutorial"))
+                                             guides))
+                          (mapcar (lambda (man)
+                                    (pcase-let ((`(,name . ,url) man))
+                                      (cons (concat name " (App)") url)))
+                                  mans)
+                          (erldoc-parse-eeps-index))
+                  (current-buffer)))
+            (write-region nil nil file nil nil nil 'ask)))
+        (setq erldoc-user-guides (with-temp-buffer (insert-file-contents file)
+                                                   (read (current-buffer)))))))
+
+;;;###autoload
+(defun erldoc-browse-topic (topic)
+  (interactive
+   (list (completing-read "User guide: " (erldoc-user-guides) nil t)))
+  (browse-url (cdr (assoc topic (erldoc-user-guides)))))
+
+(provide 'erldoc)
+;;; erldoc.el ends here
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