Error: undefined method `parse' for class JSON::Ext::Parser

[alphavector]

Output of brew config

HOMEBREW_VERSION: 4.4.16
ORIGIN: https://github.com/Homebrew/brew
HEAD: 4c9de7d31c6d9e67c4496c3c156e84c3649fec4c
Last commit: 2 days ago
Branch: stable
Core tap JSON: 15 Jan 21:06 UTC
Core cask tap JSON: 15 Jan 21:06 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_EDITOR: vim
HOMEBREW_MAKE_JOBS: 10
Homebrew Ruby: 3.3.6 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.3.6/bin/ruby
CPU: 10-core 64-bit arm_firestorm_icestorm
Clang: 16.0.0 build 1600
Git: 2.39.5 => /Library/Developer/CommandLineTools/usr/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 15.2-arm64
CLT: 16.2.0.0.1.1733547573
Xcode: N/A
Rosetta 2: false

Output of brew doctor

Error: undefined method `parse' for class JSON::Ext::Parser
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/3.3.0/gems/json-2.9.1/lib/json/common.rb:221:in `parse'
/opt/homebrew/Library/Homebrew/os/mac/sdk.rb:124:in `read_sdk_version'
/opt/homebrew/Library/Homebrew/os/mac/sdk.rb:61:in `block in all_sdks'
/opt/homebrew/Library/Homebrew/os/mac/sdk.rb:58:in `each'
/opt/homebrew/Library/Homebrew/os/mac/sdk.rb:58:in `all_sdks'
/opt/homebrew/Library/Homebrew/extend/os/mac/diagnostic.rb:460:in `check_broken_sdks'
/opt/homebrew/Library/Homebrew/cmd/doctor.rb:59:in `block in run'
/opt/homebrew/Library/Homebrew/cmd/doctor.rb:52:in `each'
/opt/homebrew/Library/Homebrew/cmd/doctor.rb:52:in `run'
/opt/homebrew/Library/Homebrew/brew.rb:94:in `<main>'
Please report this issue:
  https://docs.brew.sh/Troubleshooting

Description of issue

brew stopped working altogether

[jacktose]

I'm getting this too, for brew doctor, brew config, and usually—but not always—brew update.
Not for brew list, brew outdated, or brew developer.

I'm unclear what caused this. It started a couple weeks ago when 1) homebrew updated and I 2) tapped homebrew/core and 3) turned on brew developer to work on a PR.

$ brew update
==> Updating Homebrew...
Installing from the API is now the default behaviour!
You can save space and time by running:
  brew untap homebrew/core
Error: undefined method `parse' for class JSON::Ext::Parser
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/vendor/bundle/ruby/3.3.0/gems/json-2.9.1/lib/json/common.rb:221:in `parse'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/api.rb:99:in `fetch_json_api_file'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/api/formula.rb:59:in `download_and_cache_data!'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/api/formula.rb:133:in `write_names_and_aliases'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/cmd/update-report.rb:136:in `output_update_report'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/cmd/update-report.rb:33:in `run'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/brew.rb:95:in `<main>'
Please report this issue:
  https://docs.brew.sh/Troubleshooting

$ brew update
==> Updating Homebrew...
Already up-to-date.

$ brew update
==> Updating Homebrew...
Installing from the API is now the default behaviour!
You can save space and time by running:
  brew untap homebrew/core
Error: undefined method `parse' for class JSON::Ext::Parser
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/vendor/bundle/ruby/3.3.0/gems/json-2.9.1/lib/json/common.rb:221:in `parse'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/api.rb:99:in `fetch_json_api_file'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/api/formula.rb:59:in `download_and_cache_data!'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/api/formula.rb:133:in `write_names_and_aliases'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/cmd/update-report.rb:136:in `output_update_report'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/cmd/update-report.rb:33:in `run'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/brew.rb:95:in `<main>'
Please report this issue:
  https://docs.brew.sh/Troubleshooting

$ brew dr
Error: undefined method `parse' for class JSON::Ext::Parser
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/vendor/bundle/ruby/3.3.0/gems/json-2.9.1/lib/json/common.rb:221:in `parse'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/tab.rb:69:in `from_file_content'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/tab.rb:175:in `from_file_content'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/tab.rb:62:in `block in from_file'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/tab.rb:58:in `fetch'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/tab.rb:58:in `from_file'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/tab.rb:211:in `for_keg'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/keg.rb:525:in `tab'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/diagnostic.rb:839:in `block in check_deleted_formula'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/diagnostic.rb:838:in `each'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/diagnostic.rb:838:in `filter_map'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/diagnostic.rb:838:in `check_deleted_formula'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/cmd/doctor.rb:59:in `block in run'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/cmd/doctor.rb:52:in `each'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/cmd/doctor.rb:52:in `run'
/data/shared/lusers/jacktose/homebrew/Library/Homebrew/brew.rb:95:in `<main>'
Please report this issue:
  https://docs.brew.sh/Troubleshooting