Solvedbrew pkg-config files on >=10.14 assume headers in /usr/include

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• are reporting a bug others will be able to reproduce and not asking a question. If you're not sure or want to ask a question do so on our Discourse: https://discourse.brew.sh
• ran a brew command and reproduced the problem with multiple formulae? If it's a problem with a single, official formula (not cask) please file this issue at Homebrew/homebrew-core: https://github.com/Homebrew/homebrew-core/issues/new/choose. If it's a brew cask problem please file this issue at https://github.com/Homebrew/homebrew-cask/issues/new/choose. If it's a tap (e.g. Homebrew/homebrew-php) problem please file this issue at the tap.
• ran brew update and can still reproduce the problem?
• ran brew doctor, fixed all issues and can still reproduce the problem?
• ran brew config and brew doctor and included their output with your issue?

% brew doctor
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Warning: The following directories do not exist:
/usr/local/sbin

You should create these directories and change their ownership to your account.
  sudo mkdir -p /usr/local/sbin
  sudo chown -R $(whoami) /usr/local/sbin
% brew config
HOMEBREW_VERSION: 1.7.6-143-gc6acab6
ORIGIN: https://github.com/Homebrew/brew
HEAD: c6acab66feb63743fe69b38dab7dc7b90710e838
Last commit: 2 hours ago
Core tap ORIGIN: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 537f3703aa41c550edbaaf28dd280c6ec929f946
Core tap last commit: 34 minutes ago
HOMEBREW_PREFIX: /usr/local
HOMEBREW_DEV_CMD_RUN: 1
CPU: octa-core 64-bit kabylake
Homebrew Ruby: 2.3.7 => /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby
Clang: 10.0 build 1000
Git: 2.17.1 => /Applications/Xcode.app/Contents/Developer/usr/bin/git
Curl: 7.54.0 => /usr/bin/curl
macOS: 10.14-x86_64
CLT: 10.0.0.0.1.1535735448
Xcode: 10.0
XQuartz: 2.7.11 => /opt/X11

To help us debug your issue please explain:

• What you were trying to do (and why)
  I tried to build a package which uses pkg-config from Homebrew.

• What happened (include command output)
  I met an error when build:

fatal error: 'libxml/tree.h' file not found
#include <libxml/tree.h>
         ^~~~~~~~~~~~~~~
1 error generated.

It looks like pkg-config from Homebrew is not providing the correct include directory of libs shipping with macOS(Xcode and CLI tools). As the release note of Xcode 10, header files which were under /usr/include no longer exists and been moved to Xcode: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include and CLI tools: /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include.

output:

% which pkg-config
/usr/local/bin/pkg-config

% pkg-config --cflags --libs "libxml-2.0 > 2.6.17"
-I/usr/include/libxml2 -lxml2

% pkg-config --variable pcfiledir "libxml-2.0 > 2.6.17"
/usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/10.14

% cat /usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/10.14/libxml-2.0.pc 
prefix=/usr
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include
modules=1

Name: libXML
Version: 2.9.4
Description: libXML library version2.
Requires:
Libs: -L${libdir} -lxml2
Libs.private: -lz -lpthread -licucore -lm
Cflags: -I${includedir}/libxml2

I tested only with libxml2 but I believe this issue affect all libs which have pkg-config file from Homebrew Library/Homebrew/os/mac/pkgconfig/10.14, they are: libcurl.pc, libexslt.pc, libxml-2.0.pc, libxslt.pc, sqlite3.pc, zlib.pc.

• What you expected to happen

% pkg-config --cflags --libs "libxml-2.0 > 2.6.17"

should gives the correct path to the header files under Xcode or CLI tools.

• Step-by-step reproduction instructions (by running brew commands)

1. brew install pkg-config
2. pkg-config --cflags --libs "libxml-2.0 > 2.6.17"

Looks like there's a significant issue with the way SwiftPM handles pkg-config. It incorrectly handles *.pc files directly so that PKG_CONFIG_SYSTEM_INCLUDE_PATH (be it the environment variable or the baked in default) is not appropriately applied. It attempts to mimic what pkg-config does but this implementation is incomplete: https://github.com/apple/swift-package-manager/blob/d433df8bfca5e3df498b3300c2b6aee222154cd4/Sources/PackageLoading/Target%2BPkgConfig.swift#L244

The SwiftPM issue has fatal effects on macOS due to systems headers no longer being at /usr/include since Mojave (SwiftPM only filters /usr/include still).

This isn't however something macOS specific. There are multiarch Linux distros that rely on this. There's also other variables commonly used in places on Linux like PKG_CONFIG_ALLOW_SYSTEM_LIBS. SwiftPM fails to recognise any of this.

There is a general issue covering the topic at https://bugs.swift.org/browse/SR-6317, filed internally as rdar://problem/40235197.

I'll look into deleting cflags entirely until the Swift issue is fixed.

Hi folks, it looks like this also broke building Go packages that depend on pkg-config for CGO dependencies.

Some sample output from a Go project:

❯ go test ./...
# /usr/local/Homebrew/Library/Homebrew/shims/mac/super/pkg-config --cflags  -- opus opus opus opusfile opus opusfile
/usr/local/Homebrew/Library/Homebrew/shims/mac/super/pkg-config: line 6: /pkg-config/bin/pkg-config: No such file or directory
/usr/local/Homebrew/Library/Homebrew/shims/mac/super/pkg-config: line 6: exec: /pkg-config/bin/pkg-config: cannot execute: No such file or directory
/usr/local/Homebrew/Library/Homebrew/shims/mac/super/pkg-config: exit status 126

Looks like HOMEBREW_OPT isn’t set. I’d love to help—how best to?

I don't know what is going on, but export HOMEBREW_OPT=/usr/local/opt in ~/.bash_profile worked for me

@pgrenaud @mkalvas Run brew upgade imagemagick/brew upgrade imagemagick@6 and try again. Should work now.