Improve pkg-config-wrapper to support ChromiumOS sysroots

Improve pkg-config-wrapper to support ChromiumOS sysroots

http://codereview.chromium.org/4516002/show had to be reverted because it
conflicts with "old style" sysroots that are still used on the arm builders.
This is a cleaner approach that should work there.

The previous approach assumed that all variables in .pc files were relative to |prefix|. It would be a desirable thing to have but in practice a few packages don't follow this and have already dereferenced |prefix| in other variables (e.g. |libdir|). So instead of forcing |prefix|, this version keeps the original one but strips the path before '/usr' (in |prefix|) from all returned paths before prepending the sysroot path.

For example if you have foo.pc:
prefix=/build/board/usr
libdir=/build/board/usr/lib  # instead of libdir=${prefix}/lib
Libs: -L${libdir}/foo -lfoo

Then instead of forcing prefix=/usr (which doesn't fix |libdir|), we find the path before '/usr' in prefix ('/build/board'), that we strip from the returned -L flag ('/build/board/usr/lib/foo' -> '/usr/lib/foo') before prepending the sysroot path (-> '/path/to/sysroot/usr/lib/foo').

BUG=None
TEST=build with sysroot=/path/to/chromiumos/chroot/build/x86-generic

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=66712

[Evan Martin, 2010-11-18 22:19:00]

Can you make the review description describe what it does?

http://codereview.chromium.org/5105005/diff/1/build/linux/pkg-config-wrapper
File build/linux/pkg-config-wrapper (right):

http://codereview.chromium.org/5105005/diff/1/build/linux/pkg-config-wrapper#...
build/linux/pkg-config-wrapper:1: #!/bin/bash
Can you add some comments at the top of this explaining what it's for?

Also needs a license block.

[piman, 2010-11-18 23:05:28]

http://codereview.chromium.org/5105005/diff/1/build/linux/pkg-config-wrapper
File build/linux/pkg-config-wrapper (right):

http://codereview.chromium.org/5105005/diff/1/build/linux/pkg-config-wrapper#...
build/linux/pkg-config-wrapper:1: #!/bin/bash
On 2010/11/18 22:19:00, Evan Martin wrote:
> Can you add some comments at the top of this explaining what it's for?
> 
> Also needs a license block.

Done.

[Evan Martin, 2010-11-18 23:36:11]

This looks kinda fragile to me -- I wonder why we can't just fix the .pc files,
but the code LGTM.

[piman, 2010-11-19 00:20:28]

On Thu, Nov 18, 2010 at 3:36 PM, <evan@chromium.org> wrote:

> This looks kinda fragile to me -- I wonder why we can't just fix the .pc
> files,
>

Each of them is hard, and there's quite a few of those.
For example, one of them that's broken is gtk. The root (I think) is from
the gtk ebuild:

# need libdir here to avoid a double slash in a path that libtool doesn't
# grok so well during install (// between $EPREFIX and usr ...)
 econf --libdir="${EPREFIX}/usr/$(get_libdir)" ${myconf}

Ubuntu does it too, though they don't say why:

# configure flags
configure_flags := \
--prefix=/usr \
--libdir=/$(LIBDIR) \
 --mandir=\$${prefix}/share/man \
--infodir=\$${prefix}/share/info \
--sysconfdir=/etc \
 --enable-test-print-backend \
--enable-introspection=no \
--build=$(DEB_BUILD_GNU_TYPE)

(look at the result in /usr/lib/pkgconfig/gtk+-2.0.pc on lucid).

Now, I'm sure it's possible to fix libtool wherever it's broken, upstream
that, then patch all the relevant rules/ebuild/etc. and upstream that too,
but I'm not sure what that would break instead, and that's a lot of work for
something we can fix easily this way, and we have to live with already
existing broken .pc files.


> but the code LGTM.
>
>
> http://codereview.chromium.org/5105005/
>