wip: see if there's some logging we're missing

Cargo.lock

@@ -2554,6 +2554,7 @@ dependencies = [
  "tokio-util",
  "tower-http",
  "tracing",
+ "tracing-appender",
  "tracing-subscriber",
  "uuid",
 ]
@@ -4665,6 +4666,18 @@ dependencies = [
  "tracing-core",
 ]
 
+[[package]]
+name = "tracing-appender"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3566e8ce28cc0a3fe42519fc80e6b4c943cc4c8cef275620eb8dac2d3d4e06cf"
+dependencies = [
+ "crossbeam-channel",
+ "thiserror",
+ "time",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "tracing-attributes"
 version = "0.1.26"
@@ -4698,12 +4711,12 @@ dependencies = [
 
 [[package]]
 name = "tracing-log"
-version = "0.1.3"
+version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "78ddad33d2d10b1ed7eb9d1f518a5674713876e97e5bb9b7345a7984fbb4f922"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
 dependencies = [
- "lazy_static",
  "log",
+ "once_cell",
  "tracing-core",
 ]
 
@@ -4719,9 +4732,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-subscriber"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "30a651bc37f915e81f087d86e62a18eec5f79550c7faff886f7090b4ea757c77"
+checksum = "ad0f048c97dbd9faa9b7df56362b8ebcaa52adb06b498c050d2f4e32f90a7a8b"
 dependencies = [
  "matchers",
  "nu-ansi-term",

magic-nix-cache/Cargo.toml

@@ -32,6 +32,7 @@ tempfile = "3.9"
 uuid = { version = "1.4.0", features = ["serde", "v7", "rand", "std"] }
 futures = "0.3"
 async-compression = "0.4"
+tracing-appender = "0.2.3"
 
 [dependencies.tokio]
 version = "1.28.0"

magic-nix-cache/src/api.rs

@@ -57,6 +57,12 @@ async fn workflow_finish(
         }
     }
 
+    // NOTE(cole-h): see `init_logging`
+    let logfile = std::env::temp_dir().join("magic-nix-cache-tracing.log");
+    let logfile_contents = std::fs::read_to_string(logfile)?;
+    println!("Every log line throughout the lifetime of the program:");
+    println!("\n{logfile_contents}\n");
+
     let reply = WorkflowFinishResponse {};
 
     //state.metrics.num_new_paths.set(num_new_paths);

magic-nix-cache/src/main.rs

@@ -35,6 +35,8 @@ use tempfile::NamedTempFile;
 use tokio::process::Command;
 use tokio::sync::{oneshot, Mutex, RwLock};
 use tracing_subscriber::filter::EnvFilter;
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
 
 use gha_cache::Credentials;
 
@@ -137,8 +139,6 @@ struct StateInner {
 }
 
 async fn main_cli() -> Result<()> {
-    init_logging();
-
     let args = Args::parse();
 
     let metrics = Arc::new(telemetry::TelemetryReport::new());
@@ -439,13 +439,15 @@ async fn post_build_hook(out_paths: &str) -> Result<()> {
 
 #[tokio::main]
 async fn main() -> Result<()> {
+    let _guard = init_logging()?;
+
     match std::env::var("OUT_PATHS") {
         Ok(out_paths) => post_build_hook(&out_paths).await,
         Err(_) => main_cli().await,
     }
 }
 
-fn init_logging() {
+fn init_logging() -> Result<tracing_appender::non_blocking::WorkerGuard> {
     let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| {
         #[cfg(debug_assertions)]
         return EnvFilter::new("info")
@@ -456,11 +458,27 @@ fn init_logging() {
         return EnvFilter::new("info");
     });
 
-    tracing_subscriber::fmt()
+    let stderr_layer = tracing_subscriber::fmt::layer()
         .with_writer(std::io::stderr)
-        .pretty()
+        .pretty();
-        .with_env_filter(filter)
+
+    let logfile = std::env::temp_dir().join("magic-nix-cache-tracing.log");
+    let file = std::fs::OpenOptions::new()
+        .create(true)
+        .append(true)
+        .open(logfile)?;
+    let (nonblocking, guard) = tracing_appender::non_blocking(file);
+    let file_layer = tracing_subscriber::fmt::layer()
+        .with_writer(nonblocking)
+        .pretty();
+
+    tracing_subscriber::registry()
+        .with(filter)
+        .with(stderr_layer)
+        .with(file_layer)
         .init();
+
+    Ok(guard)
 }
 
 #[cfg(debug_assertions)]