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When upgrading to Elixir 1.19 with Erlang/OTP 28, the deployment failed with a cryptic error:

** (Mix) Could not write configuration file because it has invalid terms Application: :cors_plug Key: :origin Invalid value: ~r/.*\.jumpcomedy\.com$/ Reason: you must use the /E modifier to store regexes

The fix was simple - just add one characters:

config :cors_plug,  - origin: ~r/.*\.jumpcomedy\.com$/  + origin: ~r/.*\.jumpcomedy\.com$/E

But why did this break? And what does that /E actually do?

continue reading on zarar.dev

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