Automatically disable colors when tracing to a file

Cargo.lock

@@ -3555,6 +3555,7 @@ name = "zebrad"
 version = "3.0.0-alpha.0"
 dependencies = [
  "abscissa_core",
+ "atty",
  "chrono",
  "color-eyre",
  "dirs",

zebrad/Cargo.toml

@@ -39,6 +39,7 @@ metrics-exporter-prometheus = "0.1.0-alpha.10"
 
 dirs = "3.0.1"
 inferno = { version = "0.10.2", default-features = false }
+atty = "0.2.14"
 
 [build-dependencies]
 vergen = "3.1.0"

zebrad/src/components/tracing/component.rs

@@ -21,9 +21,12 @@ impl Tracing {
         let filter = config.filter.unwrap_or_else(|| "".to_string());
         let flame_root = &config.flamegraph;
 
+        // Only use color if tracing output is being sent to a terminal
+        let use_color = config.use_color && atty::is(atty::Stream::Stdout);
+
         // Construct a tracing subscriber with the supplied filter and enable reloading.
         let builder = FmtSubscriber::builder()
-            .with_ansi(config.use_color)
+            .with_ansi(use_color)
             .with_env_filter(filter)
             .with_filter_reloading();
         let filter_handle = builder.reload_handle();

zebrad/src/config.rs

@@ -45,7 +45,11 @@ pub struct ZebradConfig {
 pub struct TracingSection {
     /// Whether to use colored terminal output, if available.
     ///
-    /// Defaults to `true`.
+    /// Colored terminal output is automatically disabled if an output stream
+    /// is connected to a file. (Or another non-terminal device.)
+    ///
+    /// Defaults to `true`, which automatically enables colored output to
+    /// terminals.
     pub use_color: bool,
 
     /// The filter used for tracing events.