[nongnu] scratch/rfc-mode e34df2b983 46/52: Free rfc-mode-browse of the dependency on Helm

[Stefan Monnier]

branch: scratch/rfc-mode
commit e34df2b9835778ac5f69ccf57a7fd00730835567
Author: Jonas Bernoulli <jonas@bernoul.li>
Commit: Nicolas Martyanoff <khaelin@gmail.com>

    Free rfc-mode-browse of the dependency on Helm
    
    Packages that are not intrinsically tied to some completion mode,
    should not depend on such a package, to avoid forcing the authors
    preference on innocent users.
    
    This change shouldn't disturb existing users because we keep using
    `helm' if it is available.
    
    Usually optional `helm' support should be implemented in a separate
    library, which should be distributed as a separate package, but since
    here `helm' support consists of only two short functions, we can skip
    that here.
---
 rfc-mode.el | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 56 insertions(+), 6 deletions(-)

diff --git a/rfc-mode.el b/rfc-mode.el
index d031cb8144..d4556c0ff2 100644
--- a/rfc-mode.el
+++ b/rfc-mode.el
@@ -3,7 +3,7 @@
 ;; Author: Nicolas Martyanoff <khaelin@gmail.com>
 ;; URL: https://github.com/galdor/rfc-mode
 ;; Version: 1.3.0
-;; Package-Requires: ((emacs "25.1") (helm "3.2"))
+;; Package-Requires: ((emacs "25.1"))
 
 ;; Copyright 2019 Nicolas Martyanoff <khaelin@gmail.com>
 ;;
@@ -26,8 +26,12 @@
 ;;; Code:
 
 (require 'helm nil t)
+(require 'pcase)
 (require 'seq)
 
+(declare-function helm-build-sync-source "helm-source")
+(declare-function helm-make-actions "helm-lib")
+
 ;;; Configuration:
 
 (defgroup rfc-mode-group nil
@@ -70,6 +74,23 @@
 Assume RFC documents are named as e.g. rfc21.txt, rfc-index.txt."
   :type 'string)
 
+(defcustom rfc-mode-browse-input-function
+  (if (require 'helm nil t) 'helm 'completing-read)
+  "Function used by `rfc-mode-browse' to read user input.
+
+Only `read-number', `completing-read' and `helm' are explicitly
+supported.  Any other function is called with no arguments and
+must return an integer.
+
+Here `completion-read' works best if you use some completion
+mode that displays candidates \"vertically\" like `helm' does.
+`ivy-mode' is a popular choice.  `fido-mode' in combination
+with `icomplete-vertical-mode' should also work well."
+  :type '(choice (const read-number)
+                (const completing-read)
+                (const helm)
+                function))
+
 (defcustom rfc-mode-use-original-buffer-names nil
   "Whether RFC document buffers should have the name of the document file.
 If nil (the default) then use e.g. *rfc21*, otherwise use e.g. rfc21.txt."
@@ -212,14 +233,43 @@ Offer the number at point as default."
 
 ;;;###autoload
 (defun rfc-mode-browse ()
-  "Browse through all RFC documents referenced in the index using Helm."
+  "Browse through all RFC documents referenced in the index."
   (interactive)
   (rfc-mode--fetch-document "-index" (rfc-mode-index-path))
   (unless rfc-mode-index-entries
     (setq rfc-mode-index-entries
           (rfc-mode-read-index-file (rfc-mode-index-path))))
-  (helm :buffer "*helm rfc browser*"
-        :sources (rfc-mode-browser-helm-sources rfc-mode-index-entries)))
+  (pcase rfc-mode-browse-input-function
+    ('read-number
+     (display-buffer (rfc-mode--document-buffer
+                     (read-number "View RFC document: "
+                                  (rfc-mode--integer-at-point)))))
+    ('helm
+     (if (and (require 'helm nil t)
+             (fboundp 'helm))
+        (helm :buffer "*helm rfc browser*"
+              :sources (rfc-mode-browser-helm-sources
+                        rfc-mode-index-entries))
+       (user-error "Helm has to be installed explicitly")))
+    ('completing-read
+     (let* ((default (rfc-mode--integer-at-point))
+           (choice (completing-read
+                    "View RFC document: "
+                    (mapcar #'rfc-mode-browser-format-candidate
+                            rfc-mode-index-entries)
+                    nil nil nil nil
+                    (and default
+                         (rfc-mode-browser-format-candidate default))))
+           (number (or (and (string-match "\\`RFC\\([0-9]+\\)" choice)
+                            (string-to-number (match-string 1 choice)))
+                       (ignore-errors (string-to-number choice)))))
+       (unless number
+        (user-error
+         "%s doesn't match a complication candidate and is not a number"
+         choice))
+       (display-buffer (rfc-mode--document-buffer number))))
+    (_ (display-buffer (rfc-mode--document-buffer
+                       (funcall rfc-mode-browse-input-function))))))
 
 ;;;###autoload
 (define-derived-mode rfc-mode special-mode "rfc-mode"
@@ -313,11 +363,11 @@ no next header is found."
 
 ENTRIES is a list of RFC index entries in the browser."
   (helm-build-sync-source "RFC documents"
-    :candidates (mapcar #'rfc-mode-browser-helm-candidate entries)
+    :candidates (mapcar #'rfc-mode-browser-format-candidate entries)
     :action (helm-make-actions
              "Read" #'rfc-mode-browser-helm-entry-read)))
 
-(defun rfc-mode-browser-helm-candidate (entry)
+(defun rfc-mode-browser-format-candidate (entry)
   "Create a Helm candidate for ENTRY.
 
 ENTRY is a RFC index entry in the browser."