Allow passing command line params via environment (fixes #4603) (#4729)

* Allow passing command line params via environment (fixes #4603)

* add prefix

---------

Co-authored-by: SleeplessOne1917 <28871516+SleeplessOne1917@users.noreply.github.com>

Cargo.toml

@@ -165,7 +165,7 @@ urlencoding = "2.1.3"
 enum-map = "2.7"
 moka = { version = "0.12.7", features = ["future"] }
 i-love-jesus = { version = "0.1.0" }
-clap = { version = "4.5.4", features = ["derive"] }
+clap = { version = "4.5.4", features = ["derive", "env"] }
 pretty_assertions = "1.4.0"
 
 [dependencies]

src/lib.rs

@@ -70,23 +70,25 @@ use url::Url;
   about = "A link aggregator for the fediverse",
   long_about = "A link aggregator for the fediverse.\n\nThis is the Lemmy backend API server. This will connect to a PostgreSQL database, run any pending migrations and start accepting API requests."
 )]
+// TODO: Instead of defining individual env vars, only specify prefix once supported by clap.
+//       https://github.com/clap-rs/clap/issues/3221
 pub struct CmdArgs {
   /// Don't run scheduled tasks.
   ///
   /// If you are running multiple Lemmy server processes, you probably want to disable scheduled tasks on
   /// all but one of the processes, to avoid running the tasks more often than intended.
-  #[arg(long, default_value_t = false)]
+  #[arg(long, default_value_t = false, env = "LEMMY_DISABLE_SCHEDULED_TASKS")]
   disable_scheduled_tasks: bool,
   /// Disables the HTTP server.
   ///
   /// This can be used to run a Lemmy server process that only performs scheduled tasks or activity sending.
-  #[arg(long, default_value_t = false)]
+  #[arg(long, default_value_t = false, env = "LEMMY_DISABLE_HTTP_SERVER")]
   disable_http_server: bool,
   /// Disable sending outgoing ActivityPub messages.
   ///
   /// Only pass this for horizontally scaled setups.
   /// See https://join-lemmy.org/docs/administration/horizontal_scaling.html for details.
-  #[arg(long, default_value_t = false)]
+  #[arg(long, default_value_t = false, env = "LEMMY_DISABLE_ACTIVITY_SENDING")]
   disable_activity_sending: bool,
   /// The index of this outgoing federation process.
   ///
@@ -96,12 +98,12 @@ pub struct CmdArgs {
   /// Make you have exactly one server with each `i` running, otherwise federation will randomly send duplicates or nothing.
   ///
   /// See https://join-lemmy.org/docs/administration/horizontal_scaling.html for more detail.
-  #[arg(long, default_value_t = 1)]
+  #[arg(long, default_value_t = 1, env = "LEMMY_FEDERATE_PROCESS_INDEX")]
   federate_process_index: i32,
   /// How many outgoing federation processes you are starting in total.
   ///
   /// If set, make sure to set --federate-process-index differently for each.
-  #[arg(long, default_value_t = 1)]
+  #[arg(long, default_value_t = 1, env = "LEMMY_FEDERATE_PROCESS_COUNT")]
   federate_process_count: i32,
 }