問題
$ brew update
をしたら以下のエラーが出た。
Error: homebrew-core is a shallow clone. To `brew update` first run: git -C "/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core" fetch --unshallow 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. 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!
解決
メッセージにある通り実行する。
git -C "/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core" fetch --unshallow
以下の記事にエラー内容が詳しく書かれている。
[brew update]Error:homebrew-core is a shallow clone.で失敗するのを解決 - Qiita
