librsvg: prepend cairo.pc path to PKG_CONFIG_PATH

[2bits]

librsvg depends on gtk, and when pkgconfig checks gtk-2.0.pc it
queries cairo.pc. The problem is that cairo.pc is prepended
to PKG_CONFIG_PATH on 10.7 because cairo is keg-only. On 10.8
cairo is not keg-only. So there is no prepend, causing compile
errors.

Add a prepend to PKG_CONFIG_PATH to the keg directory for cairo.pc.
Tested on 10.8.1 using XCode-4.4.1, XQuartz-2.7.2, and clang.

Fixes #14474

[Sharpie]

On 10.8 cairo is not keg-only. So there is no prepend, causing compile errors.

But if Cairo is not keg-only on 10.8, then its pkg-config file should be linked into /usr/local/lib/pkgconfig which is a place that is checked by a Homebrew-installed pkg-config.

[2bits]

Yea, it's the order of the items on the PATH:

Before

PKG_CONFIG_PATH=/usr/local/Cellar/libffi/3.0.11/lib/pkgconfig:/opt/X11/share/pkgconfig:/opt/X11/lib/pkgconfig:/usr/local/Library/Homebrew/pkgconfig

After cairo's directory is prepended:

PKG_CONFIG_PATH=/usr/local/Cellar/cairo/1.12.2/lib/pkgconfig:/usr/local/Cellar/libffi/3.0.11/lib/pkgconfig:/opt/X11/share/pkgconfig:/opt/X11/lib/pkgconfig:/usr/local/Library/Homebrew/pkgconfig

That guarantees that when we force gtk to use HB cairo on all OSX systems, we force librsvg to find cairo in the cellar before it finds cairo in /opt/x11. Does that make any sense? Jack might have explained it better in the issue.

[2bits]

I'm not even sure I have this right. So I'm glad you're asking btw.

[jacknagel]

@Sharpie

But if Cairo is not keg-only on 10.8, then its pkg-config file should be linked into /usr/local/lib/pkgconfig which is a place that is checked by a Homebrew-installed pkg-config.

This is true, but because librsvg depends on XQuartz, the XQuartz pkgconfig directory is placed on PKG_CONFIG_PATH, and thus its libs are picked up before any brewed libs.

The goal is to ensure everything from the bottom up is using the same cairo, namely ours.

I've sent a message to the pkg-config mailing list asking for a PKG_CONFIG_FALLBACK_PATH, where we could place the X11 path instead and thus ensure that Homebrew's libs are always picked up first, so we'll see how receptive they are to that.

[Sharpie]

XQuartz pkgconfig directory is placed on PKG_CONFIG_PATH

Admittedly, I haven't installed XQuartz, but doesn't it install to /opt/x11? If so, why don't we build pkg-config with #{MacOS:X11.lib/pkgconfig} at the end of the default paths?

Hell, we could even stick /usr/lib/pkgconfig at the end as well.

[jacknagel]

If so, why don't we build pkg-config with #{MacOS:X11.lib/pkgconfig} at the end of the default paths?

We stopped doing this in order to support both Apple's X11 or the upstream XQuartz distro. Since they can be installed after pkg-config is built, we can't guess which one is the right one.

Hell, we could even stick /usr/lib/pkgconfig at the end as well.

We already do this.

[Sharpie]

We stopped doing this in order to support both Apple's X11 or the upstream XQuartz distro.

Well, how about just:

<Homebrew pkgconfig>:<XQuartz pkgconfig>:<Apple X11 pkgconfig>:/usr/lib/pkgconfig

Following the assumption that if a user takes the time to install XQuartz, they prefer it to whatever Apple version may or may not be hanging around.

[jacknagel]

I worry that if they are both installed, having both of them on the search path will cause even more problems; we're bound to end up with packages with linkages to both.

[Sharpie]

That may be true. But I think that adding code to this and every other formula that uses X11is the wrong way to solve a problem that is not specific to one formula.

[jacknagel]

I'm not arguing in favor of that as a long term solution. As I stated earlier I am actively trying to pkg-config's functionality extended to support our circumstances.

[2bits]

brew deps librsvg shows cairo. So why couldn't the formula installer just prepend the path in the cellar to cairo.pc onto PKG_CONFIG_PATH when it knows that? If we always want HB cairo.pc to be found, it seems reasonable until the devs reply to Jack.

[jacknagel]

We only do that for keg-only deps, because it shouldn't be necessary otherwise. I don't want to add any hacks like that to Homebrew-core. I'm OK with doing it in formulae as a stopgap measure, though, until a clean solution is arrived at.

But seriously, a patch to add a PKG_CONFIG_FALLBACK_PATH to pkg-config is like 4 LOC.

[2bits]

I'm closing this because librsvg works ok now with superenv.