Error on brew install caskformula/caskformula/inkscape: Invalid Formula on Mojave 10.14.6

[kabamwboyer]

I see the following error when I attempt to brew install caskformula/caskformula/inkscape as per the instructions here:

$ brew install caskformula/caskformula/inkscape
Error:
  homebrew-cask is a shallow clone.
To `brew update`, first run:
  git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask fetch --unshallow
This command may take a few minutes to run due to the large size of the repository.
This restriction has been made on GitHub's request because updating shallow
clones is an extremely expensive operation due to the tree layout and traffic of
Homebrew/homebrew-core and Homebrew/homebrew-cask. We don't do this for you
automatically to avoid repeatedly performing an expensive unshallow operation in
CI systems (which should instead be fixed to not use shallow clones). Sorry for
the inconvenience!
==> Tapping caskformula/caskformula
Cloning into '/usr/local/Homebrew/Library/Taps/caskformula/homebrew-caskformula'...
remote: Enumerating objects: 78, done.
remote: Total 78 (delta 0), reused 0 (delta 0), pack-reused 78
Unpacking objects: 100% (78/78), done.
Error: Invalid formula: /usr/local/Homebrew/Library/Taps/caskformula/homebrew-caskformula/Formula/inkscape.rb
inkscape: private method `include?' called for #<BuildOptions:0x00007f87581b6610>
Error: Cannot tap caskformula/caskformula: invalid syntax in tap!

but when I brew install inkscape, It appears successful:

$ brew install inkscape
Error:
  homebrew-cask is a shallow clone.
To `brew update`, first run:
  git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask fetch --unshallow
This command may take a few minutes to run due to the large size of the repository.
This restriction has been made on GitHub's request because updating shallow
clones is an extremely expensive operation due to the tree layout and traffic of
Homebrew/homebrew-core and Homebrew/homebrew-cask. We don't do this for you
automatically to avoid repeatedly performing an expensive unshallow operation in
CI systems (which should instead be fixed to not use shallow clones). Sorry for
the inconvenience!
==> Downloading https://media.inkscape.org/dl/resources/file/Inkscape-1.0.2.dmg
######################################################################## 100.0%
==> Installing Cask inkscape
==> Moving App 'Inkscape.app' to '/Applications/Inkscape.app'
==> Linking Binary 'inkscape.wrapper.sh' to '/usr/local/bin/inkscape'
🍺  inkscape was successfully installed!

I'm currently running MacOS Mojave 10.14.6 (18G3020)

[danielrbunch]

I had this same issue today, running Big Sur 11.2.3

Using the brew install inkscape worked:

brew install inkscape
==> Tapping homebrew/cask
Cloning into '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask'...
remote: Enumerating objects: 8, done.
remote: Counting objects: 100% (8/8), done.
remote: Compressing objects: 100% (6/6), done.
remote: Total 563852 (delta 2), reused 3 (delta 2), pack-reused 563844
Receiving objects: 100% (563852/563852), 248.73 MiB | 10.98 MiB/s, done.
Resolving deltas: 100% (398221/398221), done.
Tapped 3899 casks (4,016 files, 266.8MB).
==> Downloading https://media.inkscape.org/dl/resources/file/Inkscape-1.0.2.dmg
######################################################################## 100.0%
==> Installing Cask inkscape
==> Moving App 'Inkscape.app' to '/Applications/Inkscape.app'
==> Linking Binary 'inkscape.wrapper.sh' to '/usr/local/bin/inkscape'
🍺 inkscape was successfully installed!

[gitchhiker]

Same issue today, on macOS Catalina 10.15.6, the command brew install caskformula/caskformula/inkscape as hinted at on the inkscape release page does not work.
What fixed it for me was

brew tap homebrew/cask
brew install --cask inkscape

from this github thread