homebrew: accept keg-only packages as installed

[HesselM]

fixes #764 #513 #490 (and others)

As suggested by @NikolausDemmel in his comment :

The issue is that qt5 is keg-only and rosdep marks it as "not installed", when it in fact, it is installed yet not symlinked as mentioned by brew during (re)installation:

==> Reinstalling qt 
==> Pouring qt-5.15.2.catalina.bottle.tar.gz
==> Caveats
We agreed to the Qt open source license for you.
If this is unacceptable you should uninstall.

qt is keg-only, which means it was not symlinked into /usr/local,
because Qt 5 has CMake issues when linked.

If you need to have qt first in your PATH, run:
  echo 'export PATH="/usr/local/opt/qt/bin:$PATH"' >> /Users/Electroozz/.bash_profile

For compilers to find qt you may need to set:
  export LDFLAGS="-L/usr/local/opt/qt/lib"
  export CPPFLAGS="-I/usr/local/opt/qt/include"

For pkg-config to find qt you may need to set:
  export PKG_CONFIG_PATH="/usr/local/opt/qt/lib/pkgconfig"

As a result, Rosdep fails:

$ rosdep install -i --from-path src --rosdistro foxy -y
executing command [brew install qt5]
Warning: qt 5.15.2 is already installed and up-to-date.
To reinstall 5.15.2, run:
  brew reinstall qt
ERROR: the following rosdeps failed to install
  homebrew: Failed to detect successful installation of [qt5]

By checking if a package is keg-only when no linked keg is found, packages like Qt are accepted and rosdep finished clean.

[codecov-io]

Codecov Report

Merging #799 (5d2fe81) into master (d6c44cb) will decrease coverage by 0.06%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #799      +/-   ##
==========================================
- Coverage   74.93%   74.87%   -0.07%     
==========================================
  Files          42       42              
  Lines        3280     3283       +3     
==========================================
  Hits         2458     2458              
- Misses        822      825       +3     

Impacted Files	Coverage Δ
src/rosdep2/platforms/osx.py	51.08% <0.00%> (-0.85%)	⬇️

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[nuclearsandwich]

@HesselM thanks for opening this PR and proposing changes to improve the situation with homebrew. My main concern with the change as proposed is keg-only dependencies will require additional setup to be usable and rosdep may mask that fact by reporting keg-only packages as installed.

I think we definitely need keg-only packages to be recognized as installed but does it make sense to print an info message when a dependency is found as keg-only?

[wjwwood]

I think it's important to have some notice to the user that the formula is keg-only and that rosdep hasn't resolved that issue, but maybe the caveat output of Homebrew during the rosdep install is sufficient?

I don't feel strongly about it.

[wjwwood]

lgtm once the conceptual question is resolved.

[scpeters]

I think it's important to have some notice to the user that the formula is keg-only and that rosdep hasn't resolved that issue, but maybe the caveat output of Homebrew during the rosdep install is sufficient?

I don't feel strongly about it.

Using keg-only formulae often requires adding some extra paths to environment variables (see this bit of code from the scripts for build.osrfoundation.org for an example). I was going to suggest the caveats printed by Homebrew as well, which can be viewed with brew info:

$ brew info qt@5
qt@5: stable 5.15.2 (bottled) [keg-only]
Cross-platform application and UI framework
https://www.qt.io/
...
==> Caveats
We agreed to the Qt open source license for you.
If this is unacceptable you should uninstall.

qt@5 is keg-only, which means it was not symlinked into /usr/local,
because this is an alternate version of another formula.

If you need to have qt@5 first in your PATH, run:
  echo 'export PATH="/usr/local/opt/qt@5/bin:$PATH"' >> /Users/scpeters/.bash_profile

For compilers to find qt@5 you may need to set:
  export LDFLAGS="-L/usr/local/opt/qt@5/lib"
  export CPPFLAGS="-I/usr/local/opt/qt@5/include"

For pkg-config to find qt@5 you may need to set:
  export PKG_CONFIG_PATH="/usr/local/opt/qt@5/lib/pkgconfig"

[scpeters]

I think this code will return True for any keg-only formula, even if it's not actually installed. Do you want to use the installed field instead?

note that the caveats field in the json does not match the full output printed by brew info. I believe running brew ruby -e 'require "caveats"; puts Caveats.new("qt@5".f).keg_only_text' can generate the full caveats string