Fail on error parsing RUST_LOG

crates/fj-app/src/main.rs

@@ -16,6 +16,8 @@ mod args;
 mod config;
 mod path;
 
+use std::{env, error::Error};
+
 use anyhow::{anyhow, Context};
 use fj_export::export;
 use fj_host::Parameters;
@@ -28,16 +30,9 @@ use tracing_subscriber::EnvFilter;
 use crate::{args::Args, config::Config};
 
 fn main() -> anyhow::Result<()> {
- // Respect `RUST_LOG`. If that's not defined or erroneous, log warnings and
- // above.
- //
- // It would be better to fail, if `RUST_LOG` is erroneous, but I don't know
- // how to distinguish between that and the "not defined" case.
+ // Respect `RUST_LOG`. If that's not defined, log warnings and above. Fail if it's erroneous.
  tracing_subscriber::fmt()
- .with_env_filter(
- EnvFilter::try_from_default_env()
- .unwrap_or_else(|_| EnvFilter::new("WARN")),
- )
+ .with_env_filter(try_default_env_filter()?)
  .event_format(format().pretty())
  .init();
 
@@ -75,3 +70,29 @@ fn no_model_error() -> anyhow::Error {
  - Specify a default model in the configuration file."
  )
 }
+
+fn try_default_env_filter() -> anyhow::Result<EnvFilter> {
+ let env_filter = EnvFilter::try_from_default_env();
+
+ match env_filter {
+ Ok(env_filter) => Ok(env_filter),
+
+ Err(err) => {
+ if let Some(kind) = err.source() {
+ if let Some(env::VarError::NotPresent) =
+ kind.downcast_ref::<env::VarError>()
+ {
+ return Ok(EnvFilter::new("WARN"));
+ }
+ } else {
+ // `tracing_subscriber::filter::FromEnvError` currently returns a source
+ // in all cases.
+ unreachable!()
+ }
+
+ Err(anyhow!(
+ "There was an error parsing the RUST_LOG environment variable."
+ ))
+ }
+ }
+}