fix(log): no ANSI colour codes unless stderr is a terminal

src/main.rs

@@ -1,4 +1,5 @@
 use clap::Parser;
+use std::io::IsTerminal;
 use tracing_subscriber::EnvFilter;
 
 mod cli;
@@ -63,6 +64,10 @@ fn main() {
             EnvFilter::try_from_default_env().unwrap_or_else(|_| "bugsee_cli=info".into()),
         )
         .with_writer(std::io::stderr)
+        .with_ansi(ansi_enabled(
+            std::io::stderr().is_terminal(),
+            std::env::var_os("NO_COLOR").as_deref(),
+        ))
         .init();
 
     let runtime = match tokio::runtime::Builder::new_multi_thread()
@@ -87,3 +92,28 @@ fn main() {
     });
     std::process::exit(code.as_i32());
 }
+
+/// Colour only an interactive terminal: Xcode / Gradle / CI logs and the
+/// detached `bugsee-cli.log` file would otherwise be full of escape codes.
+/// Honours <https://no-color.org> (any non-empty `NO_COLOR` disables colour).
+fn ansi_enabled(stderr_is_terminal: bool, no_color: Option<&std::ffi::OsStr>) -> bool {
+    stderr_is_terminal && no_color.is_none_or(|v| v.is_empty())
+}
+
+#[cfg(test)]
+mod ansi_tests {
+    use super::ansi_enabled;
+    use std::ffi::OsStr;
+
+    #[test]
+    fn colour_only_on_a_terminal() {
+        assert!(ansi_enabled(true, None));
+        assert!(!ansi_enabled(false, None));
+    }
+
+    #[test]
+    fn no_color_disables_colour_unless_empty() {
+        assert!(!ansi_enabled(true, Some(OsStr::new("1"))));
+        assert!(ansi_enabled(true, Some(OsStr::new(""))));
+    }
+}

tests/no_ansi_when_piped.rs

@@ -0,0 +1,30 @@
+//! Log output must carry no ANSI escape codes unless stderr is a terminal.
+//!
+//! Xcode, Gradle and CI capture stderr into logs, and the detached daemon writes
+//! it to `bugsee-cli.log`; escape codes there are noise. Under `assert_cmd` stderr
+//! is a pipe, so any ESC byte means the `with_ansi(...)` wiring in `main` regressed.
+
+mod common;
+
+/// `sourcemaps inject` on an empty directory needs no network and logs one info line.
+#[test]
+fn piped_stderr_has_no_escape_codes() {
+    let dir = tempfile::tempdir().unwrap();
+    let out = common::cli()
+        .env("RUST_LOG", "bugsee_cli=info")
+        .env_remove("NO_COLOR")
+        .args(["sourcemaps", "inject"])
+        .arg(dir.path())
+        .assert()
+        .success();
+    let stderr = out.get_output().stderr.clone();
+    let text = String::from_utf8_lossy(&stderr);
+    assert!(
+        text.contains("sourcemaps inject complete"),
+        "expected a log line on stderr, got: {text:?}"
+    );
+    assert!(
+        !stderr.contains(&0x1b),
+        "stderr contains ANSI escapes: {text:?}"
+    );
+}