bug#10472: [PATCH] realpath: fix problems with // handling

[Pádraig Brady]

On 02/04/2012 07:05 PM, Eric Blake wrote:
> On platforms like Cygwin where / and // are distinct, realpath was
> incorrectly collapsing // into /.  http://debbugs.gnu.org/10472.
> 
> * src/realpath.c (path_common_prefix): When // is special, treat /
> and // as having no common match.
> (relpath): Allow for no match even without --relative-base.
> ---
> 
> This is the coreutils side of the patch; for this to work, we also
> have to upgrade to the latest gnulib.
> 
> I'm not pushing this until we decide what to do about testing; I
> guess we've already figured out how to make basename and dirname
> tests conditional on whether they are on Linux or Cygwin (that is,
> whether // and / are the same or different), so I should do something
> similar to that for the realpath test.  But I can at least get a
> code review on realpath.c while figuring out the testing situation.
> 
>  src/realpath.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/src/realpath.c b/src/realpath.c
> index 2dc5e11..f06fbcc 100644
> --- a/src/realpath.c
> +++ b/src/realpath.c
> @@ -131,6 +131,10 @@ path_common_prefix (const char *path1, const char *path2)
>    int i = 0;
>    int ret = 0;
> 
> +  if (DOUBLE_SLASH_IS_DISTINCT_ROOT && *path1 == '/' && *path2 == '/'
> +      && (path1[1] == '/') != (path2[1] == '/'))
> +    return 0;
> +
>    while (*path1 && *path2)
>      {
>        if (*path1 != *path2)
> @@ -168,6 +172,9 @@ relpath (const char *can_fname)
> 
>        /* Skip the prefix common to --relative-to and path.  */
>        int common_index = path_common_prefix (can_relative_to, can_fname);
> +      if (!common_index)
> +        return false;
> +
>        const char *relto_suffix = can_relative_to + common_index;
>        const char *fname_suffix = can_fname + common_index;
> 

is the DOUBLE_SLASH_IS_DISTINCT_ROOT check needed in realpath.c
I.E. if we get a leading // then that define is implicit?

Also doesn't path_prefix() need the same adjustment,
so as to verify --relative-base in the same way?

cheers,
Pádraig.