Re: [PATCH 4/7] Add join_paths() to safely concatenate paths.

[Jonathan Nieder <jrnieder@gmail.com>]

Hi,

Michael G. Schwern wrote:

> Otherwise you might wind up with things like...
>
>     my $path1 = undef;
>     my $path2 = 'foo';
>     my $path = $path1 . '/' . $path2;
>
> creating '/foo'.  Or this...
>
>     my $path1 = 'foo/';
>     my $path2 = 'bar';
>     my $path = $path1 . '/' . $path2;
>
> creating 'foo//bar'.

I'm still puzzled by this one, too.  I don't understand the
motivation.  Is this to make joining paths less fragile, by preserving
the property that join_paths($a, $b) names the directory you would get
to by first chdir-ing into $a and then into $b?

It would be easier to understand as two patches: first, one that
extracts join_paths without any functional change, and then one that
changes its implementation with an explanation for what positive
functional effect that would have.

> --- a/git-svn.perl
> +++ b/git-svn.perl
[...]
> @@ -1275,7 +1276,7 @@ sub get_svnprops {
>  	$path = $cmd_dir_prefix . $path;
>  	fatal("No such file or directory: $path") unless -e $path;
>  	my $is_dir = -d $path ? 1 : 0;
> -	$path = $gs->{path} . '/' . $path;
> +	$path = join_paths($gs->{path}, $path);
>  
>  	# canonicalize the path (otherwise libsvn will abort or fail to
>  	# find the file)

This can't be for the //-collapsing effect since the path is about
to be canonicalized.  It can't be for the initial-/ effect since
that is stripped away by canonicalization, too.

So no functional effect here, good or bad.

[...]
> --- a/perl/Git/SVN.pm
> +++ b/perl/Git/SVN.pm
[...]
> @@ -316,9 +320,7 @@ sub init_remote_config {
>  			}
>  			my $old_path = $self->path;
>  			$url =~ s!^\Q$min_url\E(/|$)!!;
> -			if (length $old_path) {
> -				$url .= "/$old_path";
> -			}
> +			$url = join_paths($url, $old_path);
>  			$self->path($url);

This is probably not for the normal //-collapsing effect because
$url already has its trailing / stripped off.  Maybe it is for
cases where $old_path has leading slashes or $min_url has multiple
trailing ones?

In the end it shouldn't make a difference, once a later patch teaches
Git::SVN->path to canonicalize.

Is the functional change in this patch for aesthetic reasons, or is
there some other component (perhaps in a later patch) that relies on
it?

Thanks again for your help,
Jonathan