[PATCH] editor: use canonicalized absolute path

[Ramkumar Ramachandra <artagnon@gmail.com>]

By improving the relative_path() algorithm, e02ca72 (path.c: refactor
relative_path(), not only strip prefix, 2013-06-25) uncovered a latent
bug.  While most editor applications like cat and vim handle
non-canonicalized relative paths fine, emacs does not.  This is due to a
long-standing bug in emacs, where it refuses to resolve symlinks in the
supplied path:

  #!/bin/sh
  mkdir z z/a z/b
  echo moodle >z/a/file
  ln -s z/b
  cd b
  emacs ../a/file # fail: opens /tmp/a/file

Even if emacs were to be patched to fix this bug now, we still need to
support users running older versions.

Co-authored-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 Urgent candidate for maint.  I wrote to emacs-devel, but nobody seems
 to be interested; the sources are horrendously unmaintainable, and
 the project should die soon.

 editor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/editor.c b/editor.c
index 27bdecd..0abbd8d 100644
--- a/editor.c
+++ b/editor.c
@@ -37,7 +37,7 @@ int launch_editor(const char *path, struct strbuf *buffer, const char *const *en
 		return error("Terminal is dumb, but EDITOR unset");
 
 	if (strcmp(editor, ":")) {
-		const char *args[] = { editor, path, NULL };
+		const char *args[] = { editor, real_path(path), NULL };
 		struct child_process p;
 		int ret, sig;
 
-- 
1.8.4.rc0.2.g7ba4592