The diff-goto-source function doesn't work on context diff or unified diff
hunks when the context is set to 0 lines and when the hunk is only changing
a single line.

Example hunks which it fails on are this, generated using (let
((diff-switches "-c0")) (diff "/tmp/1" "/tmp/2")) :

diff -c0 /tmp/1 /tmp/2
*** /tmp/1      Sat Sep  8 15:44:04 2007
--- /tmp/2      Sat Sep  8 15:44:04 2007
***************
*** 4 ****
! one
--- 4 ----
! two

and this, generated using (let ((diff-switches "-u0")) (diff "/tmp/1"
"/tmp/2")) :

diff -u0 /tmp/1 /tmp/2
--- /tmp/1      2007-09-08 15:44:04.000000000 +0200
+++ /tmp/2      2007-09-08 15:44:04.000000000 +0200
@@ -4 +4 @@
-one
+two

I've fixed this bug.  The fix is to make parts of the regexps optional, and
to code what to do in the event that they're missing.

The patch is here: http://dooglus.rincevent.net/random/emacs-diff-patch.txt

I'll paste it here as well, in case you're reading this off-line.

I've signed papers with the FSF for my contributions to Emacs.

Chris.

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*** /home/chris/programs/emacs/lisp/diff-mode.el	Sat Sep  8 15:29:54 2007
--- /tmp/diff-mode.el	Sat Sep  8 15:40:53 2007
***************
*** 1217,1242 ****

         ;; A context diff.
         ((eq (char-after) ?*)
!         (if (not (looking-at "\\*\\{15\\}\\(?: .*\\)?\n\\*\\*\\*
\\([0-9]+\\),\\([0-9]+\\) \\*\\*\\*\\*"))
              (error "Unrecognized context diff first hunk header format")
            (forward-line 2)
            (diff-sanity-check-context-hunk-half
!            (1+ (- (string-to-number (match-string 2))
!                   (string-to-number (match-string 1)))))
!           (if (not (looking-at "--- \\([0-9]+\\),\\([0-9]+\\) ----$"))
                (error "Unrecognized context diff second hunk header format")
              (forward-line)
              (diff-sanity-check-context-hunk-half
!              (1+ (- (string-to-number (match-string 2))
!                     (string-to-number (match-string 1))))))))

         ;; A unified diff.
         ((eq (char-after) ?@)
          (if (not (looking-at
!                   "@@ -[0-9]+,\\([0-9]+\\) \\+[0-9]+,\\([0-9]+\\) @@"))
              (error "Unrecognized unified diff hunk header format")
!           (let ((before (string-to-number (match-string 1)))
!                 (after (string-to-number (match-string 2))))
              (forward-line)
              (while
                  (case (char-after)
--- 1217,1246 ----

         ;; A context diff.
         ((eq (char-after) ?*)
!         (if (not (looking-at "\\*\\{15\\}\\(?: .*\\)?\n\\*\\*\\*
\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\)? \\*\\*\\*\\*"))
              (error "Unrecognized context diff first hunk header format")
            (forward-line 2)
            (diff-sanity-check-context-hunk-half
! 	   (if (match-string 2)
! 	       (1+ (- (string-to-number (match-string 2))
! 		      (string-to-number (match-string 1))))
! 	     1))
!           (if (not (looking-at "---
\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\)? ----$"))
                (error "Unrecognized context diff second hunk header format")
              (forward-line)
              (diff-sanity-check-context-hunk-half
! 	     (if (match-string 2)
! 		 (1+ (- (string-to-number (match-string 2))
! 			(string-to-number (match-string 1))))
! 	       1)))))

         ;; A unified diff.
         ((eq (char-after) ?@)
          (if (not (looking-at
!                   "@@ -[0-9]+\\(?:,\\([0-9]+\\)\\)?
\\+[0-9]+\\(?:,\\([0-9]+\\)\\)? @@"))
              (error "Unrecognized unified diff hunk header format")
!           (let ((before (if (match-string 1) (string-to-number
(match-string 1)) 1))
!                 (after (if (match-string 2) (string-to-number
(match-string 2)) 1)))
              (forward-line)
              (while
                  (case (char-after)

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