Re: [PATCH] diff: don't attempt to strip prefix from absolute Windows paths

[Junio C Hamano <gitster@pobox.com>]

Johannes Sixt <j6t@kdbg.org> writes:

> Use is_absolute_path() to detect Windows style absolute paths.

When cd676a51 ("diff --relative: output paths as relative to the
current subdirectory", 2008-02-12) was done, neither "is_dir_sep()"
nor "has_dos_drive_prefix()" existed---the latter had to wait until
25fe217b ("Windows: Treat Windows style path names.", 2008-03-05),
but we didn't notice that the above code needs to use the Windows
aware is_absolute_path() when we applied the change.

> One might wonder whether the check for a directory separator that
> is visible in the patch context should be changed from == '/' to
> is_dir_sep() or not. It turns out not to be necessary. That code
> only ever investigates paths that have undergone pathspec
> normalization, after which there are only forward slashes even on
> Windows.

Thanks for carefully explaining.

>  static void strip_prefix(int prefix_length, const char **namep, const char **otherp)
>  {
>  	/* Strip the prefix but do not molest /dev/null and absolute paths */
> -	if (*namep && **namep != '/') {
> +	if (*namep && !is_absolute_path(*namep)) {
>  		*namep += prefix_length;
>  		if (**namep == '/')
>  			++*namep;
>  	}
> -	if (*otherp && **otherp != '/') {
> +	if (*otherp && !is_absolute_path(*otherp)) {
>  		*otherp += prefix_length;
>  		if (**otherp == '/')
>  			++*otherp;

When I read the initial report and guessed the root cause without
looking at the code, I didn't expect the problematic area to be this
isolated and the solution to be this simple.

Nicely done.