configure finds libpng but matplotlib does not

[mkoeppe]

This happens at least in the following situation: Sage 9.1.beta9 on OS X, using the system's rather than Sage's Python, no pkg-config installed.

CC: @jhpalmieri @dimpase @orlitzky

Component: build: configure

Author: Matthias Koeppe

Branch: 0ac76c3

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29448

[jhpalmieri]

Description changed:

--- 
+++ 
@@ -1 +1 @@
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+This happens at least in the following situation: Sage 9.1.beta9 on OS X, using the system's rather than Sage's Python, no pkg-config installed.

[mkoeppe]

comment:5

Could you try if #29444 (Upgrade matplotlib to 2.2.5) fixes it?

[orlitzky]

comment:6

What exactly failed?

[jhpalmieri]

comment:7

Replying to @mkoeppe:

Could you try if #29444 (Upgrade matplotlib to 2.2.5) fixes it?

I will, but I ran into #29449 first.

Replying to @orlitzky:

What exactly failed?

I see this in the matplotlib log file:

                            * The following required packages can not be built:
                            * png
                            * Try installing png with `brew install libpng` and
                            * pkg-config with `brew install pkg-config`

and then the build fails.

[jhpalmieri]

comment:8

Same problem with the upgrade to 2.2.5.

[jhpalmieri]

comment:9

Note that installing Sage's pkgconf package does not fix this.

[dimpase]

comment:10

This looks to me like an issue with Homebrew installing packages in a non-standard location, and then they get mixed up with system packages.

It should be totally indifferent whether it is using Sage's pkgconf (providing pkg-config), or system's pkg-config, they both do exactly the same thing (if not, it's a bug in our management of its PKG_CONFIG_PATH).

[mkoeppe]

comment:11

libpng.pc is unusual in that it Requires: zlib but there are two versions of zlib.pc on homebrew. By default, the one representing the system zlib is used; if one uses . .homebrew-build-env, which adds to PKG_CONFIG_PATH, the one for homebrew's zlib is used.

[mkoeppe]

comment:12

Possibly related: build error of sagelib,

[sagelib-9.1.beta9]     raise PackageNotFoundError(package)
[sagelib-9.1.beta9] pkgconfig.pkgconfig.PackageNotFoundError: libpng not found

reported at https://groups.google.com/d/msg/sage-support/Oh3ev_wrjyo/od4R2FCNDQAJ

[mkoeppe]

comment:13

It's likely the same thing: spkg-configure.m4 has a sneaky way of finding libpng but does not tell any of the other packages - matplotlib and now sagelib.

[dimpase]

comment:15

if we use Homebrew, can we just bail out if pkg-config is not installed?

[mkoeppe]

comment:16

No, that's not the correct solution.

If an spkg-configure has more general ways of finding a library than one of the spkgs depending on it, then spkg-configure needs to communicate the install information to that spkg.

[dimpase]

comment:17

Replying to @mkoeppe:

No, that's not the correct solution.

If an spkg-configure has more general ways of finding a library than one of the spkgs depending on it, then spkg-configure needs to communicate the install information to that spkg.

you say that reinventing the wheel is the correct solution...

Writing tricky autoconf code, where the user can simply do brew install pkg-config, seems to be a waste of time to me.

[mkoeppe]

comment:18

No, the problem is that the autoconf code is already too tricky and finds more libpng than the spkgs that it is guarding.

[dimpase]

comment:19

The code I wrote there assumed that users are sane, and install a meaningful set of tools. You propose to make it dumber to make it work in pathological cases, I don't get why this is needed, sorry.