Elixir .gitignore template

Almost every rule here begins with a slash, anchoring it to the directory holding the ignore file. That matters in an umbrella project, where each application has its own _build and deps: the root ignore file covers the root ones, and the anchoring keeps the intent explicit rather than relying on a rule that happens to match everywhere.

/_build holds compiled bytecode organised by environment, so a project ends up with separate dev, test and prod trees. /deps holds the fetched source of every dependency. Both are rebuilt from the mix file and the lockfile, and the lockfile is the one you commit: it pins exact versions and hashes so a fetch today matches a fetch next year.

*.beam is the compiled bytecode format for the virtual machine, and *.ez is a packaged archive of beam files. erl_crash.dump is the crash dump written when the runtime terminates abnormally. It contains the state of every process at the moment of death, including message queues, which can easily include user data or a token that was in flight.

/config/*.secret.exs is the important one. The convention is that a secret config file holds the database password, the endpoint signing salt and any third party keys, imported by the environment specific config. Ignoring it is right, and the companion habit is to commit an example version with the keys present and the values blank so a new developer knows what to supply.

/priv/static is the compiled asset output for a web project: bundled JavaScript, processed stylesheets and the digest manifest. It is produced by the asset build from sources that are tracked, and committing it means every style change appears twice in the diff. .elixir_ls is the language server's working directory, holding a build of the project purely for editor features.