Please run brew install --debug ... and paste the output.

/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::TapLoader): loading /usr/local/Homebrew/Library/Taps/lvillani/homebrew-tap/Formula/carthage-copy-frameworks.rb
==> Installing carthage-copy-frameworks from lvillani/tap
/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::AliasLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/python.rb
/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/pkg-config.rb
/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/gdbm.rb
/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/openssl@1.1.rb
/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/readline.rb
/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/sqlite.rb
/usr/local/Homebrew/Library/Homebrew/brew.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/xz.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::FromPathLoader): loading /usr/local/Homebrew/Library/Taps/lvillani/homebrew-tap/Formula/carthage-copy-frameworks.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::AliasLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/python.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/gdbm.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/openssl@1.1.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/readline.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/sqlite.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/xz.rb
/usr/local/Homebrew/Library/Homebrew/build.rb (Formulary::FormulaLoader): loading /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/pkg-config.rb
==> Downloading https://github.com/lvillani/carthage-copy-frameworks/archive/v2.0.0.tar.gz
/usr/bin/curl -q --globoff --show-error --user-agent Homebrew/2.2.8\ \(Macintosh\;\ Intel\ Mac\ OS\ X\ 10.15.3\)\ curl/7.64.1 --location --silent --head --request GET https://github.com/lvillani/carthage-copy-frameworks/archive/v2.0.0.tar.gz
Already downloaded: /Users/tka/Library/Caches/Homebrew/downloads/882ec6d16c8039878574289d942d75a8476d63d117aa79a10dee7c756b26795b--carthage-copy-frameworks-2.0.0.tar.gz
tar xof /Users/tka/Library/Caches/Homebrew/downloads/882ec6d16c8039878574289d942d75a8476d63d117aa79a10dee7c756b26795b--carthage-copy-frameworks-2.0.0.tar.gz -C /private/tmp/d20200304-30341-115o0ha
cp -pR /private/tmp/d20200304-30341-115o0ha/carthage-copy-frameworks-2.0.0/. /private/tmp/carthage-copy-frameworks-20200304-30341-1vlvys/carthage-copy-frameworks-2.0.0
/usr/local/Homebrew/Library/Homebrew/language/python.rb:177:in `virtualenv_install_with_resources'
NoMethodError: undefined method `delete' for nil:NilClass
1. raise
2. backtrace
3. shell
Choose an action:

CC @iMichka that https://github.com/lvillani/homebrew-tap/blob/master/Formula/carthage-copy-frameworks.rb is no longer a valid formula after the Python changes.

Ah that's good news, so we could fork that one over there and could modify it according to your changes. Could you give us a hint what should be changed? I highly believe it has something to do with the virtualenv usage. Still, we couldn't find any information at all that there were breaking changes released, that's a bit sad :( Thanks a lot for your fast response!!

Could you give us a hint what should be changed?

I'm not sure anything needs to be changed, I need @iMichka to verify why this is an error. It's likely a bug.

I can have a look in 3-4 hours when I am back. I am travelling right now, but I will be able to connect in the train back home.

Here is the failing code: https://github.com/Homebrew/brew/blob/master/Library/Homebrew/language/python.rb#L168-L181

depends_on "python@3"

That's unusual. It should be depends_on "python" or depends_on "python@3.8"

That's not relevant here, both version descriptions are valid. I just found out that for the case if you want to build from source or your formula does not contain a bottle brew is broke right now.

Can easily be tested with any python formula which uses virtualenv_install_with_resources, for instance brew install --build-from-source git-revise. We also got other ci processes which fail because of that.

Here is the failing code: https://github.com/Homebrew/brew/blob/master/Library/Homebrew/language/python.rb#L168-L181

The removal of python = wanted.first || "python2.7" is problematic. Now wanted isn't used at all and python won't be set at all in that if block.

@Bo98 Good catch, could you submit a PR?

Thanks for all the quick help! Nice catch @Bo98!

#7116.

@MikeMcQuaid Is there any ETA für an upcoming release? As mentioned above, all Python builds are currently broken if there exists no bottle or building from sources.

@benjohnde There is a new release now.

That's super awesome! Thanks a million for the quick help ❤️!

Thanks all for the fixes ! :)

We're seeing the same issue with one of our internal packages. We're also using virtualenv_install_with_resources but our package depends on python 2, not python 3. We're also using the latest brew version, which should have @Bo98 's fix.

$ brew --version
Homebrew 2.2.9-23-g78140ce

What's interesting is if we change depends_on "python@2" to depends_on "python@3", the package installs (but our python code isn't compatible with python 3, so this isn't really a fix).

Unfortunately, our package and formula aren't open source. But I was able to reproduce by copying the formula mentioned in this bug report to a personal tap, and changing the dependency to python@2.

You can therefore reproduce this ongoing bug using the following command:

$ brew install mitch-seymour/tap/carthage-copy-frameworks
==> Auto-updated Homebrew!
Updated 1 tap (mitch-seymour/tap).
No changes to formulae.

Updating Homebrew...
==> Installing carthage-copy-frameworks from mitch-seymour/tap
==> Downloading https://github.com/lvillani/carthage-copy-frameworks/archive/v2.0.0.tar.gz
Already downloaded: /Users/mseymour/Library/Caches/Homebrew/downloads/882ec6d16c8039878574289d942d75a8476d63d117aa79a10dee7c756b26795b--carthage-copy-frameworks-2.0.0.tar.gz
Error: An exception occurred within a child process:
  NoMethodError: undefined method `delete' for nil:NilClass

That'll be because Homebrew no longer has any knowledge of what "python@2" is and thus does not recognise it as a Python formula.

You could use virtualenv_install_with_resources, :using => "python2".

Thanks @Bo98 , that fixed our issue :)