bug#1976: 23.0.50; PC-do-completion should fix case if possible

[Denis Howe]

My 2007-10-03 attempt to get this patch applied got no further than RMS's request for someone to DTRT.  It took several hours of my time to debug and test, and the bug still bites me every time I re-install, so PLEASE could someone apply it?  Thanks.
------------------------------------------------------------
In the latest complete.el from CVS (v1.94), function "PC-do-completion" fails to correct the case of the input being completed when:

- "completion-ignore-case" is true and
- "read-file-name-completion-ignore-case" is true and

- all possible completions have the same case

Ordinary completion preserves input case only where the potential completions differ in case.  If they agree then ordinary completion changes the input case to that of the prefix.

For example, evaluate:

(partial-completion-mode 0)
(setq completion-ignore-case t)
(completing-read "Input: " '(("Den".1)("Denis".2)) nil t "d")

Hitting TAB runs ordinary "minibuffer-complete" which completes "d" to "Den" (case corrected).

Enable partial completion:

(partial-completion-mode 1)

Re-evaluate the above completing-read.

Hitting TAB now runs "PC-complete" which completes "d" to "den" (fails to correct input case).

I've tested the attached patch thoroughly.  Please contact me if you want any more background on this.

------------------------------------------------------------

ChangeLog entry:

2009-01-21  Denis Howe <denis.howe@gmail.com>

       * complete.el (PC-do-completion): Correct case when unambiguous.

------------------------------------------------------------

cvs diff -cw complete.el
Index: complete.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/complete.el,v
retrieving revision 1.94
diff -c -w -r1.94 complete.el
*** complete.el    9 Jan 2009 04:44:19 -0000    1.94
--- complete.el    21 Jan 2009 14:21:17 -0000
***************
*** 737,744 ****
               (setq prefix (PC-try-completion
                     (PC-chunk-after basestr skip) poss)))
          (let ((first t) i)
-           ;; Retain capitalization of user input even if
-           ;; completion-ignore-case is set.
            (if (eq mode 'word)
                (setq prefix (PC-chop-word prefix basestr)))
            (goto-char (+ beg (length dirname)))
--- 737,742 ----
***************
*** 746,760 ****
                  (setq i 0) ; index into prefix string
                  (while (< i (length prefix))
                    (if (and (< (point) end)
                         (eq (downcase (aref prefix i))
!                            (downcase (following-char))))
!                       ;; same char (modulo case); no action
!                       (forward-char 1)
!                     (if (and (< (point) end)
                           (and (looking-at " ")
                                                    (memq (aref prefix i)
!                             PC-delims-list)))
                      ;; replace " " by the actual delimiter
                      (progn
                        (delete-char 1)
                        (insert (substring prefix i (1+ i))))
--- 744,757 ----
                  (setq i 0) ; index into prefix string
                  (while (< i (length prefix))
                    (if (and (< (point) end)
+                                            (or
                         (eq (downcase (aref prefix i))
!                                                 (downcase (following-char)))
                           (and (looking-at " ")
                                                    (memq (aref prefix i)
!                                                        PC-delims-list))))
                      ;; replace " " by the actual delimiter
+                                       ;; or input char by prefix char
                      (progn
                        (delete-char 1)
                        (insert (substring prefix i (1+ i))))
***************
*** 766,772 ****
                                                 (setq end (1- end))))
                      (setq improved t)
                                          (insert (substring prefix i (1+ i)))
!                     (setq end (1+ end)))))
                    (setq i (1+ i)))
                  (or pt (setq pt (point)))
                  (looking-at PC-delim-regex))
--- 763,769 ----
                                                 (setq end (1- end))))
                      (setq improved t)
                                          (insert (substring prefix i (1+ i)))
!                                       (setq end (1+ end))))
                    (setq i (1+ i)))
                  (or pt (setq pt (point)))
                  (looking-at PC-delim-regex))

------------------------------------------------------------
End

-- Denis Howe <denis.howe@gmail.com>