Flag packages that depend on Pillow for special installation steps

[jbarlow83]

Homebrew requires a special installation procedure to ensure that the correction combination of dependencies from Apple system libraries and Homebrew libraries are selected. Pillow is also a popular and widely used library so this special case is likely to occur often enough in practice.

It would be helpful if poet advised users that Pillow needs special procedures and that one should search for a recently updated formula in homebrew-core and copy that.

Provided no other packages need special steps, it could also reproduce the boilerplate to install Pillow, which is as follows:

  depends_on "freetype"
  depends_on "jpeg"

  [...] snip

  def install
    venv = virtualenv_create(libexec, "python3")

    resource("Pillow").stage do
      inreplace "setup.py" do |s|
        sdkprefix = MacOS::CLT.installed? ? "" : MacOS.sdk_path
        s.gsub! "openjpeg.h", "probably_not_a_header_called_this_eh.h"
        s.gsub! "ZLIB_ROOT = None", "ZLIB_ROOT = ('#{sdkprefix}/usr/lib', '#{sdkprefix}/usr/include')"
        s.gsub! "JPEG_ROOT = None", "JPEG_ROOT = ('#{Formula["jpeg"].opt_prefix}/lib', '#{Formula["jpeg"].opt_prefix}/include')"
        s.gsub! "FREETYPE_ROOT = None", "FREETYPE_ROOT = ('#{Formula["freetype"].opt_prefix}/lib', '#{Formula["freetype"].opt_prefix}/include')"
      end

      # avoid triggering "helpful" distutils code that doesn't recognize Xcode 7 .tbd stubs
      ENV.append "CFLAGS", "-I#{MacOS.sdk_path}/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers" unless MacOS::CLT.installed?
      venv.pip_install Pathname.pwd
    end

    res = resources.map(&:name).to_set - ["Pillow"]

    res.each do |r|
      venv.pip_install resource(r)
    end
  end

[tdsmith]

What happens if you don't do anything special for Pillow?

[jbarlow83]

Good question. Without the patch, Pillow's setup.py will use pkg-config to attempt to locate the libraries and it needs, and will link differently depending on what the user has installed, so it may or may not work. Also, as the "avoid triggering" comment implies, it works around a bug affecting distutils and Xcode 7.

That being said, I didn't develop this, I just know about it because the homebrew-core team added it to my formula. @fxcoudert may be able to add further detail.