internal: remove spurious regex dependency

- replace tokio's env-filter with a smaller&simpler targets filter
- reshuffle logging infra a bit to make sure there's only a single place
  where we read environmental variables
- use anyhow::Result in rust-analyzer binary

crates/hir-ty/src/tests.rs

@@ -30,7 +30,7 @@ use syntax::{
     ast::{self, AstNode, HasName},
     SyntaxNode,
 };
-use tracing_subscriber::{layer::SubscriberExt, EnvFilter, Registry};
+use tracing_subscriber::{layer::SubscriberExt, Registry};
 use tracing_tree::HierarchicalLayer;
 use triomphe::Arc;
 
@@ -52,7 +52,8 @@ fn setup_tracing() -> Option<tracing::subscriber::DefaultGuard> {
         return None;
     }
 
-    let filter = EnvFilter::from_env("CHALK_DEBUG");
+    let filter: tracing_subscriber::filter::Targets =
+        env::var("CHALK_DEBUG").ok().and_then(|it| it.parse().ok()).unwrap_or_default();
     let layer = HierarchicalLayer::default()
         .with_indent_lines(true)
         .with_ansi(false)