Re: RUNTIME_PREFIX references in gitconfig variable paths

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Paul,

[late reply, I know, sorry about that!]

On Wed, 4 Jul 2018, Paul Smith wrote:

> On Wed, 2018-07-04 at 13:26 +0200, Johannes Schindelin wrote:
> > On Wed, 4 Jul 2018, Paul Smith wrote:
> > 
> > > One thing I wanted to do was provide a default ca-bundle.crt file
> > > along with my local build of Git.  I need my installation to be
> > > relocatable and I'm using RUNTIME_PREFIX with Git 2.18.0 (on
> > > GNU/Linux).
> > 
> > Understandable. We do this all the time in Git for Windows. Our
> > config entry has this form:
> > 
> >         [http]
> >                 sslCAinfo = /ssl/certs/ca-bundle.crt
> > 
> > and in the RUNTIME_PREFIX mode, this will be made relative to the
> > runtime prefix. It is my understanding that bf9acba (http: treat
> > config options sslCAPath and sslCAInfo as paths, 2015-11-23) makes
> > this work.
> 
> Hm.  Unless I'm missing something this doesn't happen (and indeed, it
> does not work for me; with:
> 
>   [http]
>       sslcainfo = /etc/ca-bundle.crt
> 
> I get:
> 
>   fatal: unable to access 'https://github.com/myrepo.git/': error
> setting certificate verify locations:
>     CAfile: /etc/ca-bundle.crt
>     CApath: none
> 
> although it works if I use a fully-qualified pathname, and using strace
> I find the process never attempted to access any other path for ca-
> bundle.crt).
> 
> In http.c we see how this path is treated in http_options():
> 
>         if (!strcmp("http.sslcainfo", var))
>                 return git_config_pathname(&ssl_cainfo, var, value);
> 
> I can't tell exactly how this function is invoked, but the result
> (ssl_cainfo) is used here without further modification:
> 
>         curl_easy_setopt(result, CURLOPT_CAINFO, ssl_cainfo);
> 
> In config.c we find get_config_pathname() which does this:
> 
>         *dest = expand_user_path(value, 0);
> 
> In path.c we find expand_user_path() which does this:
> 
>         if (path == NULL)
>                 goto return_null;
>         if (path[0] == '~') {
>             ...
>         }
>         strbuf_addstr(&user_path, to_copy);
>         return strbuf_detach(&user_path, NULL);
> 
> I don't see any reference to system_prefix(), system_path(), etc. which
> would be needed to RUNTIME_PREFIX-ize things.

I finally got around to dig into this, and found out what is
happening: in https://github.com/git/git/blob/v2.19.0/http.c#L295-L296,
the http.sslcainfo setting is handled by calling git_config_pathname(),
which in turn calls expand_user_path() to handle special cases
(https://github.com/git/git/blob/v2.19.0/config.c#L1067-L1075). And it
is this function which has a specific, special handling on Windows
(which, like so many other changes that are waiting patiently for the
slow upstreaming process, has not made it into any *Git* version yet),
see https://github.com/git-for-windows/git/commit/434b76522de1:

@@ -709,6 +710,10 @@ char *expand_user_path(const char *path, int real_home)

        if (path == NULL)
		goto return_null;
+#ifdef __MINGW32__
+       if (path[0] == '/')
+               return system_path(path + 1);
+#endif
        if (path[0] == '~') {
                const char *first_slash = strchrnul(path, '/');
                const char *username = path + 1;

This explains why it works on Windows, but not elsewhere...

Now, I could imagine that this special handling makes a ton of sense not
for *Git for Windows*, but rather for RUNTIME_PREFIX.

So maybe we should replace that `__MINGW32__` condition by
`RUNTIME_PREFIX`? What do you think?

Ciao,
Johannes