Hi all,

I’m seeing some unexpected recompilation behavior in dev, and I’m not sure what’s causing it.

Here’s the flow:

• rm -rf _build deps .elixir_ls
• mix deps.get
• mix clean and mix compile
• I start my Phoenix app with MIX_DEBUG=1 iex -S mix phx.server.
• Everything boots up cleanly (already compiled).
• I haven’t modified any .ex files.
• Then, as soon as I make a request in the browser, a recompilation is triggered:

Shortly after that, a background process (in my case, an Oban plugin) crashes with an UndefinedFunctionError, because the module it depends on (like MyApp.Repo) seems to have been purged and recompiled after app startup.

Here is the output from iex just after the browser request:

    iex()>
    -> Running mix compile.elixir --purge-consolidation-path-if-stale /home/xxxxxxxx/workspace/my_app/_build/dev/lib/my_app/consolidated --no-all-warnings (inside MyApp.MixProject)
    ...
    [error] GenServer {Oban.Registry, {Oban, Oban.Sonar}} terminating
** (UndefinedFunctionError) function MyApp.Repo.query/3 is undefined (module MyApp.Repo is not available
    # ... (more similar errors)
    [notice] Application oban_met exited: shutdown
    # .... (errors)
    Compiling 432 files (.ex)
    # .... (still errors)
    <- Ran mix compile.elixir in 18412ms
    -> Running mix compile.app --purge-consolidation-path-if-stale /home/xxxxxxxx/workspace/my_app/_build/dev/lib/my_app/consolidated --no-all-warnings (inside MyApp.MixProject)
    Generated my_app app
    <- Ran mix compile.app in 6ms
    -> Running mix compile.protocols (inside MyApp.MixProject)
    <- Ran mix compile.protocols in 32ms
    [info] GET /patient/patient_records/new
    # ...
    [notice] Application my_app exited: shutdown
    iex()>

Things I’ve already tried:

• Disabled all watchers in config/dev.exs (same behaviour)
• Verified that I’m not touching any files manually.
• Confirmed that it only recompiles after an HTTP request, not on app boot.
• If I disable CodeReloader, I don’t have the recompilation…

config :my_app, MyAppWeb.Endpoint,
  code_reloader: false

So it seems like Phoenix.CodeReloader is the one triggering the recompilation but why would Phoenix.CodeReloader trigger a recompilation if no source files changed?

I have also the standard config for live_reload Endpoint

# Watch static and templates for browser reloading.
config :my_app, MyAppWeb.Endpoint,
  live_reload: [
    patterns: [
      ~r"priv/static/.*(js|css|png|jpeg|jpg|gif|svg)$",
      ~r"priv/gettext/.*(po)$",
      ~r"lib/my_app_web/(controllers|live|components)/.*(ex|heex)$"
    ]
  ]

Also note that this happened after an update to erlang 28.0.2, elixir 1.18.4 from elixir 1.17 / erlang 27.

Any insights appreciated!

Thanks