Do log during testing, but "captured" by default

- `just test` is silent
- `just test-verbose` is noisy and sequential
- CI is noisy and sequential and `trace` level

.github/workflows/test-linux.yml

@@ -51,4 +51,8 @@ jobs:
         run: cargo build
 
       - name: Run unit tests
-        run: cargo test
+        env:
+          AIR_LOG: trace
+        # `--nocapture` to see our own `tracing` logs
+        # `--test-threads 1` to ensure `tracing` logs aren't interleaved
+        run: cargo test -- --nocapture --test-threads 1

.github/workflows/test-mac.yml

@@ -29,4 +29,8 @@ jobs:
         run: cargo build
 
       - name: Run unit tests
-        run: cargo test
+        env:
+          AIR_LOG: trace
+        # `--nocapture` to see our own `tracing` logs
+        # `--test-threads 1` to ensure `tracing` logs aren't interleaved
+        run: cargo test -- --nocapture --test-threads 1

.github/workflows/test-windows.yml

@@ -29,4 +29,8 @@ jobs:
         run: cargo build
 
       - name: Run unit tests
-        run: cargo test
+        env:
+          AIR_LOG: trace
+        # `--nocapture` to see our own `tracing` logs
+        # `--test-threads 1` to ensure `tracing` logs aren't interleaved
+        run: cargo test -- --nocapture --test-threads 1

crates/lsp/src/logging.rs

@@ -28,6 +28,7 @@ use tower_lsp::lsp_types::MessageType;
 use tower_lsp::Client;
 use tracing::level_filters::LevelFilter;
 use tracing_subscriber::fmt::time::LocalTime;
+use tracing_subscriber::fmt::TestWriter;
 use tracing_subscriber::{
     fmt::{writer::BoxMakeWriter, MakeWriter},
     layer::SubscriberExt,
@@ -138,8 +139,13 @@ pub(crate) fn init_logging(
     let writer = if client_info.is_some_and(|client_info| {
         client_info.name.starts_with("Zed") || client_info.name.starts_with("Visual Studio Code")
     }) {
+        // These IDEs are known to support `window/logMessage` well
         BoxMakeWriter::new(LogWriterMaker::new(log_tx))
+    } else if is_test_client(client_info) {
+        // Ensures a standard `cargo test` captures output unless `-- --nocapture` is used
+        BoxMakeWriter::new(TestWriter::default())
     } else {
+        // Fallback for other editors / IDEs
         BoxMakeWriter::new(std::io::stderr)
     };
 
@@ -165,21 +171,26 @@ pub(crate) fn init_logging(
 
     let subscriber = tracing_subscriber::Registry::default().with(layer);
 
-    if !is_test_client(client_info) {
+    if is_test_client(client_info) {
+        // During parallel testing, `set_global_default()` gets called multiple times
+        // per process. That causes it to error, but we ignore this.
+        tracing::subscriber::set_global_default(subscriber).ok();
+    } else {
         tracing::subscriber::set_global_default(subscriber)
-            .expect("Should be able to set the global subscriber.");
+            .expect("Should be able to set the global subscriber exactly once.");
     }
 
     tracing::info!("Logging initialized with level: {log_level}");
 }
 
-/// We never log during tests as tests run in parallel within a single process,
-/// but you can only have 1 global subscriber per process.
+/// We use a special `TestWriter` during tests to be compatible with `cargo test`'s
+/// typical output capturing behavior.
 ///
-/// If you are debugging a single test, you can override this to emit messages to stderr.
+/// Important notes:
+/// - `cargo test` swallows all logs unless you use `-- --nocapture`.
+/// - Tests run in parallel, so logs can be interleaved unless you run `--test-threads 1`.
 ///
-/// Note that if you override this and run multiple tests in parallel, then the call
-/// to `set_global_default()` will error causing a panic.
+/// We use `cargo test -- --nocapture --test-threads 1` on CI because of all of this.
 fn is_test_client(client_info: Option<&ClientInfo>) -> bool {
     client_info.map_or(false, |client_info| client_info.name == "AirTestClient")
 }
@@ -253,7 +264,7 @@ impl<S> tracing_subscriber::layer::Filter<S> for LogLevelFilter {
         let filter = if meta.target().starts_with("air") || meta.target().starts_with("lsp") {
             self.filter.tracing_level()
         } else {
-            tracing::Level::INFO
+            tracing::Level::WARN
         };
 
         meta.level() <= &filter

justfile

@@ -6,13 +6,18 @@ gen-formatter:
 gen-grammar:
     cargo run -p xtask_codegen -- grammar r
 
-# Run the parser and formatter tests
+# Run the tests
 test:
-  cargo test -p air_r_parser
-  cargo test -p air_r_formatter
+  cargo test
+
+# Run the tests in verbose mode
+# `--nocapture` to see our own `tracing` logs
+# `--test-threads 1` to ensure `tracing` logs aren't interleaved
+test-verbose:
+  cargo test -- --nocapture --test-threads 1
 
 # Run the quick formatter test
-quick:
+test-quick:
   cargo test --package air_r_formatter --test quick_test -- quick_test --exact --show-output --ignored
 
 # Creates a new crate