New option 'diff-ignore-whitespace-switches'

Allows specifying the switches to use when ignoring whitespace for
those of us who don't like "-b".

* lisp/vc/diff-mode.el (diff-ignore-whitespace-switches): New defcustom.
(diff-refresh-hunk): Use it when ignoring whitespace.
* doc/emacs/files.texi (Diff Mode): Describe the new option.
* etc/NEWS: Announce the new option.

doc/emacs/files.texi

@@ -1737,10 +1737,13 @@ only the hunks within the region.
 Re-generate the current hunk (@code{diff-refresh-hunk}).
 
 @item C-c C-w
+@vindex diff-ignore-whitespace-switches
 @findex diff-ignore-whitespace-hunk
 Re-generate the current hunk, disregarding changes in whitespace.
 With a non-@code{nil} prefix arg, re-generate all the hunks
-(@code{diff-ignore-whitespace-hunk}).
+(@code{diff-ignore-whitespace-hunk}).  This calls @code{diff-command}
+with @code{diff-ignore-whitespace-switches}, which defaults to
+@samp{-b}, meaning ignore changes in whitespace only.
 
 @item C-x 4 A
 @findex diff-add-change-log-entries-other-window

etc/NEWS

@@ -106,6 +106,12 @@ When called with a non-nil prefix argument
 'diff-ignore-whitespace-hunk' now iterates over all the hunks in the
 current diff, regenerating them without whitespace changes.
 
++++
+*** New user option 'diff-ignore-whitespace-switches'.
+This allows changing which type of whitespace changes are ignored when
+regenerating hunks with 'diff-ignore-whitespace-hunk'.  Defaults to
+the previously hard-coded "-b".
+
 ** Buffer Selection
 
 ---

lisp/vc/diff-mode.el

@@ -153,6 +153,17 @@ and hunk-based syntax highlighting otherwise as a fallback."
   :type (get 'whitespace-style 'custom-type)
   :version "29.1")
 
+(defcustom diff-ignore-whitespace-switches "-b"
+  "Switch or list of diff switches to use when ignoring whitespace.
+The default \"-b\" means to ignore whitespace-only changes,
+\"-w\" means ignore all whitespace changes."
+  :type '(choice
+          (string :tag "Ignore whitespace-only changes" :value "-b")
+          (string :tag "Ignore all whitespace changes" :value "-w")
+          (string :tag "Single switch")
+          (repeat :tag "Multiple switches" (string :tag "Switch")))
+  :version "30.1")
+
 (defvar diff-vc-backend nil
   "The VC backend that created the current Diff buffer, if any.")
 
@@ -2130,7 +2141,7 @@ With non-nil prefix arg, re-diff all the hunks."
 	 (coding-system-for-read buffer-file-coding-system)
 	 opts old new)
     (when ignore-whitespace
-      (setq opts '("-b")))
+      (setq opts (ensure-list diff-ignore-whitespace-switches)))
     (when opt-type
       (setq opts (cons opt-type opts)))