@spec client_error_overlay?() :: boolean()

Returns true when the client-side runtime error overlay is enabled, false otherwise.

Controlled by the :client_error_overlay application environment key, which defaults to whatever client_stacktraces?/0 returns, so turning client diagnostics on turns both on:

config :hologram, client_error_overlay: false

When enabled, an uncaught client error renders in the page as well as in the browser console. Uncaught errors reach the console in every environment - this setting only decides whether they are also shown in the page.

Setting it to false alongside enabled stacktraces leaves the report in the console without putting an error screen in front of the app's users. The two reach different people: console output is read by whoever opens the devtools, whereas the overlay is shown to everyone who hits the error.

The value is read at compile time, so changing it requires recompiling the bundles.

@spec client_stacktraces?() :: boolean()

Returns true when client-side stacktraces are enabled, false otherwise.

Controlled by the :client_stacktraces application environment key, which defaults to true in the :dev and :test environments and false elsewhere:

config :hologram, client_stacktraces: true

When enabled, the compiler emits source metadata into the client bundle and the interpreter tracks a call stack, so errors raised on the client carry the same stacktraces as errors raised on the server. Error messages and rescue semantics are unaffected by this setting - they are identical in every environment.

Enabling it outside of :dev/:test has trade-offs: argument values appear in stacktrace frames and can leave the device via screenshots, support tickets or pasted console output, source paths reveal the project's file layout, and the compiled Elixir in a bundle is roughly a third larger over the wire.

The value is read at compile time, so changing it requires recompiling the bundles.

@spec enabled?() :: boolean()

Returns true when Hologram's runtime is enabled, false otherwise.

Hologram is always enabled outside of the :dev and :test environments. In :dev and :test it is disabled unless the HOLOGRAM_START environment variable is set to "1" (as mix holo does). When disabled, Hologram's supervision children are not started and Hologram.Router passes requests straight through to the next plug instead of trying to serve them.

@spec env() :: atom()

Returns the current environment.

@spec secret_key_base() :: String.t()

Returns the secret key base.

Uses the SECRET_KEY_BASE env var when set. In embedded mode, :dev and :test fall back to the Phoenix endpoint's configured :secret_key_base - standalone mode has no endpoint to read it from. Everywhere else the env var is required.