Fix bug #11827 with file-relative-name on MS-Windows.

 lisp/files.el (file-relative-name): Compare file names
 case-insensitively if on MS-Windows or MS-DOS, or if
 read-file-name-completion-ignore-case is non-nil.  Don't use
 case-fold-search for this purpose.

2 files changed, 14 insertions, 5 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 9373bf14fbb..74914cd973c 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,10 @@
+2012-07-01  Eli Zaretskii  <eliz@gnu.org>
+
+        * files.el (file-relative-name): Compare file names
+        case-insensitively if on MS-Windows or MS-DOS, or if
+        read-file-name-completion-ignore-case is non-nil.  Don't use
+        case-fold-search for this purpose.  (Bug#11827)
+
 2012-06-28  Andreas Schwab  <schwab@linux-m68k.org>
 
         * calendar/cal-dst.el (calendar-current-time-zone): Return
diff --git a/lisp/files.el b/lisp/files.el
index c46d7c22d92..cf9521731e2 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4310,7 +4310,9 @@ on a DOS/Windows machine, it returns FILENAME in expanded form."
                                                         default-directory))))
     (setq filename (expand-file-name filename))
     (let ((fremote (file-remote-p filename))
-          (dremote (file-remote-p directory)))
+          (dremote (file-remote-p directory))
+          (fold-case (or (memq system-type '(ms-dos cygwin windows-nt))
+                         read-file-name-completion-ignore-case)))
       (if ;; Conditions for separate trees
           (or
            ;; Test for different filesystems on DOS/Windows
@@ -4319,7 +4321,7 @@ on a DOS/Windows machine, it returns FILENAME in expanded form."
             (memq system-type '(ms-dos cygwin windows-nt))
             (or
              ;; Test for different drive letters
-             (not (eq t (compare-strings filename 0 2 directory 0 2)))
+             (not (eq t (compare-strings filename 0 2 directory 0 2 fold-case)))
              ;; Test for UNCs on different servers
              (not (eq t (compare-strings
                          (progn
@@ -4344,16 +4346,16 @@ on a DOS/Windows machine, it returns FILENAME in expanded form."
           (while (not
                   (or
                    (eq t (compare-strings filename-dir nil (length directory)
-                                          directory nil nil case-fold-search))
+                                          directory nil nil fold-case))
                    (eq t (compare-strings filename nil (length directory)
-                                          directory nil nil case-fold-search))))
+                                          directory nil nil fold-case))))
             (setq directory (file-name-directory (substring directory 0 -1))
                   ancestor (if (equal ancestor ".")
                                ".."
                              (concat "../" ancestor))))
           ;; Now ancestor is empty, or .., or ../.., etc.
           (if (eq t (compare-strings filename nil (length directory)
-                                     directory nil nil case-fold-search))
+                                     directory nil nil fold-case))
               ;; We matched within FILENAME's directory part.
               ;; Add the rest of FILENAME onto ANCESTOR.
               (let ((rest (substring filename (length directory))))