Subject: bug#21262: 25.0.50; Diff-mode gets confused about its narrowing if hunk source not found

From: [email-masked] (Charles A. Roelli)
Date: Tue, 22 Aug 2017 16:02:17 +0200

> From: [email-masked]
> Cc: Dima Kogan <[email-masked]>,  [email-masked]
> Date: Mon, 21 Aug 2017 20:18:39 -0400
>
> Looks like a reasonable fix to me (though I know only a little bit of
> diff-mode).  Here it is again ignoring whitespace, which I think makes
> it easier to see what is happening:
> 
> modified   lisp/vc/diff-mode.el
> @@ -874,6 +874,8 @@ diff-find-file-name
>      ;; Flush diff-remembered-files-alist if the default-directory is changed.
>      (set (make-local-variable 'diff-remembered-defdir) default-directory)
>      (set (make-local-variable 'diff-remembered-files-alist) nil))
> +  (save-restriction
> +    (widen)
>      (save-excursion
>        (unless (looking-at diff-file-header-re)
>          (or (ignore-errors (diff-beginning-of-file))
> @@ -919,7 +921,7 @@ diff-find-file-name
>  				   (file-name-nondirectory file)))
>               (set (make-local-variable 'diff-remembered-files-alist)
>                    (cons (cons fs file) diff-remembered-files-alist))
> -           file))))))
> +             file)))))))
> 
> Perhaps we should swap the save-restriction and save-excursion around
> though?  The elisp manual says:
> 
>      If you use both `save-restriction' and `save-excursion' together,
>      `save-excursion' should come first (on the outside).  Otherwise,
>      the old point value would be restored with temporary narrowing
>      still in effect.

Good point, thank you.  I'll apply the attached patch in a few days if
there's no further discussion.

>From aac6f9eb7aba0cc6b67b56a748e8ee25f755e8f5 Mon Sep 17 00:00:00 2001
From: "Charles A. Roelli" <[email-masked]>
Date: Tue, 22 Aug 2017 15:57:01 +0200
Subject: [PATCH] Fix 'diff-goto-source' when buffer is narrowed (Bug#21262)

* lisp/vc/diff-mode.el (diff-find-file-name): Save the current
narrowing, and widen the buffer before searching for the name of the
file corresponding to the diff.

With thanks to Noam Postavsky.
---
 lisp/vc/diff-mode.el | 92 +++++++++++++++++++++++++++-------------------------
 1 file changed, 47 insertions(+), 45 deletions(-)

diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index aa8d778..1d4af54 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -875,51 +875,53 @@ diff-find-file-name
     (set (make-local-variable 'diff-remembered-defdir) default-directory)
     (set (make-local-variable 'diff-remembered-files-alist) nil))
   (save-excursion
-    (unless (looking-at diff-file-header-re)
-      (or (ignore-errors (diff-beginning-of-file))
-	  (re-search-forward diff-file-header-re nil t)))
-    (let ((fs (diff-hunk-file-names old)))
-      (if prefix (setq fs (mapcar (lambda (f) (concat prefix f)) fs)))
-      (or
-       ;; use any previously used preference
-       (cdr (assoc fs diff-remembered-files-alist))
-       ;; try to be clever and use previous choices as an inspiration
-       (cl-dolist (rf diff-remembered-files-alist)
-	 (let ((newfile (diff-merge-strings (caar rf) (car fs) (cdr rf))))
-	   (if (and newfile (file-exists-p newfile)) (cl-return newfile))))
-       ;; look for each file in turn.  If none found, try again but
-       ;; ignoring the first level of directory, ...
-       (cl-do* ((files fs (delq nil (mapcar 'diff-filename-drop-dir files)))
-                (file nil nil))
-	   ((or (null files)
-		(setq file (cl-do* ((files files (cdr files))
-                                    (file (car files) (car files)))
-			       ;; Use file-regular-p to avoid
-			       ;; /dev/null, directories, etc.
-			       ((or (null file) (file-regular-p file))
-				file))))
-	    file))
-       ;; <foo>.rej patches implicitly apply to <foo>
-       (and (string-match "\\.rej\\'" (or buffer-file-name ""))
-	    (let ((file (substring buffer-file-name 0 (match-beginning 0))))
-	      (when (file-exists-p file) file)))
-       ;; If we haven't found the file, maybe it's because we haven't paid
-       ;; attention to the PCL-CVS hint.
-       (and (not prefix)
-	    (boundp 'cvs-pcl-cvs-dirchange-re)
-	    (save-excursion
-	      (re-search-backward cvs-pcl-cvs-dirchange-re nil t))
-	    (diff-find-file-name old noprompt (match-string 1)))
-       ;; if all else fails, ask the user
-       (unless noprompt
-         (let ((file (expand-file-name (or (car fs) ""))))
-	   (setq file
-		 (read-file-name (format "Use file %s: " file)
-				 (file-name-directory file) file t
-				 (file-name-nondirectory file)))
-           (set (make-local-variable 'diff-remembered-files-alist)
-                (cons (cons fs file) diff-remembered-files-alist))
-           file))))))
+    (save-restriction
+      (widen)
+      (unless (looking-at diff-file-header-re)
+        (or (ignore-errors (diff-beginning-of-file))
+	    (re-search-forward diff-file-header-re nil t)))
+      (let ((fs (diff-hunk-file-names old)))
+        (if prefix (setq fs (mapcar (lambda (f) (concat prefix f)) fs)))
+        (or
+         ;; use any previously used preference
+         (cdr (assoc fs diff-remembered-files-alist))
+         ;; try to be clever and use previous choices as an inspiration
+         (cl-dolist (rf diff-remembered-files-alist)
+	   (let ((newfile (diff-merge-strings (caar rf) (car fs) (cdr rf))))
+	     (if (and newfile (file-exists-p newfile)) (cl-return newfile))))
+         ;; look for each file in turn.  If none found, try again but
+         ;; ignoring the first level of directory, ...
+         (cl-do* ((files fs (delq nil (mapcar 'diff-filename-drop-dir files)))
+                  (file nil nil))
+	     ((or (null files)
+		  (setq file (cl-do* ((files files (cdr files))
+                                      (file (car files) (car files)))
+			         ;; Use file-regular-p to avoid
+			         ;; /dev/null, directories, etc.
+			         ((or (null file) (file-regular-p file))
+				  file))))
+	      file))
+         ;; <foo>.rej patches implicitly apply to <foo>
+         (and (string-match "\\.rej\\'" (or buffer-file-name ""))
+	      (let ((file (substring buffer-file-name 0 (match-beginning 0))))
+	        (when (file-exists-p file) file)))
+         ;; If we haven't found the file, maybe it's because we haven't paid
+         ;; attention to the PCL-CVS hint.
+         (and (not prefix)
+	      (boundp 'cvs-pcl-cvs-dirchange-re)
+	      (save-excursion
+	        (re-search-backward cvs-pcl-cvs-dirchange-re nil t))
+	      (diff-find-file-name old noprompt (match-string 1)))
+         ;; if all else fails, ask the user
+         (unless noprompt
+           (let ((file (expand-file-name (or (car fs) ""))))
+	     (setq file
+		   (read-file-name (format "Use file %s: " file)
+				   (file-name-directory file) file t
+				   (file-name-nondirectory file)))
+             (set (make-local-variable 'diff-remembered-files-alist)
+                  (cons (cons fs file) diff-remembered-files-alist))
+             file)))))))

 (defun diff-ediff-patch ()
-- 
2.9.4