[cargo-nextest] add a BufWriter around reporter writes

Stops lots of little syscalls from happening.

Fixes #35.

Author: sunshowers

Cargo.lock

@@ -1,7 +1,7 @@
 [package]
 name = "cargo-nextest"
 description = "A next-generation test runner for Rust."
-version = "0.9.2"
+version = "0.9.3"
 readme = "README.md"
 license = "Apache-2.0 OR MIT"
 repository = "https://github.com/nextest-rs/nextest"

cargo-nextest/Cargo.toml

@@ -12,14 +12,15 @@ use color_eyre::eyre::{Report, Result, WrapErr};
 use guppy::graph::PackageGraph;
 use nextest_runner::{
     config::NextestConfig,
+    errors::WriteEventError,
     partition::PartitionerBuilder,
     reporter::{StatusLevel, TestOutputDisplay, TestReporterBuilder},
     runner::TestRunnerBuilder,
     signal::SignalHandler,
     test_filter::{RunIgnored, TestFilterBuilder},
     test_list::{OutputFormat, RustTestArtifact, SerializableFormat, TestList},
 };
-use std::io::Cursor;
+use std::io::{BufWriter, Cursor, Write};
 use supports_color::Stream;
 
 /// A next-generation test runner for Rust.
@@ -322,7 +323,10 @@ impl AppImpl {
                 }
                 let stdout = std::io::stdout();
                 let lock = stdout.lock();
-                test_list.write(message_format.to_output_format(output.verbose), lock)?;
+                // Buffer the output to minimize syscalls.
+                let mut writer = BufWriter::new(lock);
+                test_list.write(message_format.to_output_format(output.verbose), &mut writer)?;
+                writer.flush()?;
             }
             Command::Run {
                 ref profile,
@@ -355,11 +359,11 @@ impl AppImpl {
                     .to_builder(no_capture)
                     .build(&test_list, &profile, handler);
                 let stderr = std::io::stderr();
+                let mut writer = BufWriter::new(stderr);
                 let run_stats = runner.try_execute(|event| {
-                    // TODO: consider turning this into a trait, to initialize and carry the lock
-                    // across callback invocations
-                    let lock = stderr.lock();
-                    reporter.report_event(event, lock)
+                    // Write and flush the event.
+                    reporter.report_event(event, &mut writer)?;
+                    writer.flush().map_err(WriteEventError::Io)
                 })?;
                 if !run_stats.is_success() {
                     return Err(Report::new(ExpectedError::test_run_failed()));

cargo-nextest/src/dispatch.rs

@@ -3,6 +3,13 @@
 This page documents new features and bugfixes for cargo-nextest. Please see the [stability
 policy](book/stability.md) for how versioning works with cargo-nextest.
 
+## [0.9.3] - 2022-02-14
+
+### Fixed
+
+- Add a `BufWriter` around stderr for the reporter, reducing the number of syscalls and fixing
+  issues around output overlap on Windows ([#35](https://github.com/nextest-rs/nextest/issues/35)). Thanks [@fdncred](https://github.com/fdncred) for reporting this!
+
 ## [0.9.2] - 2022-02-14
 
 ### Fixed