Installation on macOS (15.1/Catalina) (M1) fails with cairo not found.

[ChillarAnand]

I have already installed the pre-requisites.

But during install, it is failing to find "cairo".

      Compiler for C supports arguments -Wswitch-default: YES
      Compiler for C supports arguments -Wno-missing-field-initializers: YES
      Compiler for C supports arguments -Wno-unused-parameter: YES
      Compiler for C supports arguments -fno-strict-aliasing: YES
      Compiler for C supports arguments -fvisibility=hidden: YES
      Found pkg-config: YES (/opt/local/bin/pkg-config) 0.29.2
      Found CMake: /Users/chillaranand/homebrew/bin/cmake (3.30.3)
      Run-time dependency cairo found: NO (tried pkgconfig, framework and cmake)

      ../cairo/meson.build:31:12: ERROR: Dependency "cairo" not found, tried pkgconfig, framework and cmake

      A full log can be found at /private/var/folders/vb/3wyl_42s4x1_z_7swgpq9xr40000gq/T/pip-install-dr_abefi/pycairo_8e2c36b9f63e490084503233417555c7/.mesonpy-joompwi1/meson-logs/meson-log.txt
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

[Tomaubier]

Just found a fix for the same issue occurring with macOS 15.1.1, on a clean Python 3.12.7 miniconda environment.
Based on this comment I managed to defined a proper PKG_CONFIG_PATH that solved the issue. The process is a bit cumbersome though so a more long term solution is still needed.
Here s a quick run down of the procedure I had to go through for some libraries (cairo, fontconfig, freetype2, x11 and xcb in my case):

1. Check the location of a missing library by running find /opt -name <library name>.pc in the terminal.
   eg. find /opt -name cairo.pc gave me: /opt/homebrew/Cellar/cairo/1.18.2/lib/pkgconfig/cairo.pc
   If the library is not installed on your system, no paths will be returned by the command. Install the package using brew install <library name> and try again.

2. Add the library path to PKG_CONFIG_PATH
export PKG_CONFIG_PATH="<parent directory path of the missing lib>:$PKG_CONFIG_PATH"
   eg. export PKG_CONFIG_PATH="/opt/homebrew/Cellar/cairo/1.18.2/lib/pkgconfig/:$PKG_CONFIG_PATH"

3. In the same terminal session check that pkg-config finds the library by running pkg-config --libs <lib name>
   eg. pkg-config --libs cairo

4. Try installing pycairo (pip install pycairo), if the errors pops back up with a different package, repeat the process and append the new package path to PKG_CONFIG_PATH.

For reference, by the time I managed to get pycairo installed, my PKG_CONFIG_PATH looked like this:

export PKG_CONFIG_PATH="/opt/homebrew/Cellar/cairo/1.18.2/lib/pkgconfig/:/opt/homebrew/Cellar/fontconfig/2.15.0/lib/pkgconfig/:/opt/homebrew/Cellar/freetype/2.13.3/lib/pkgconfig/:/opt/homebrew/Cellar/libx11/1.8.10/lib/pkgconfig/:/opt/homebrew/share/pkgconfig/:/opt/homebrew/lib/pkgconfig/:$PKG_CONFIG_PATH"

I also this export command to my terminal config file (nano ~/.zshrc) in case I need to reinstall pycairo in an other environment.

I hope that helps!