diff --git a/tracing-subscriber/src/fmt/fmt_subscriber.rs b/tracing-subscriber/src/fmt/fmt_subscriber.rs index 9887b711ff..1b89039261 100644 --- a/tracing-subscriber/src/fmt/fmt_subscriber.rs +++ b/tracing-subscriber/src/fmt/fmt_subscriber.rs @@ -274,10 +274,32 @@ impl Subscriber { } } - /// Enable ANSI terminal colors for formatted output. - #[cfg(feature = "ansi")] - #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))] + /// Sets whether or not the formatter emits ANSI terminal escape codes + /// for colors and other text formatting. + /// + /// Enabling ANSI escapes (calling `with_ansi(true)`) requires the "ansi" + /// crate feature flag. Calling `with_ansi(true)` without the "ansi" + /// feature flag enabled will panic if debug assertions are enabled, or + /// print a warning otherwise. + /// + /// This method itself is still available without the feature flag. This + /// is to allow ANSI escape codes to be explicitly *disabled* without + /// having to opt-in to the dependencies required to emit ANSI formatting. + /// This way, code which constructs a formatter that should never emit + /// ANSI escape codes can ensure that they are not used, regardless of + /// whether or not other crates in the dependency graph enable the "ansi" + /// feature flag. pub fn with_ansi(self, ansi: bool) -> Self { + #[cfg(not(feature = "ansi"))] + if ansi { + const ERROR: &str = + "tracing-subscriber: the `ansi` crate feature is required to enable ANSI terminal colors"; + #[cfg(debug_assertions)] + panic!("{}", ERROR); + #[cfg(not(debug_assertions))] + eprintln!("{}", ERROR); + } + Subscriber { is_ansi: ansi, ..self diff --git a/tracing-subscriber/src/fmt/mod.rs b/tracing-subscriber/src/fmt/mod.rs index ba5066d2ec..38acf4d092 100644 --- a/tracing-subscriber/src/fmt/mod.rs +++ b/tracing-subscriber/src/fmt/mod.rs @@ -610,9 +610,21 @@ where } } - /// Enable ANSI terminal colors for formatted output. - #[cfg(feature = "ansi")] - #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))] + /// Sets whether or not the formatter emits ANSI terminal escape codes + /// for colors and other text formatting. + /// + /// Enabling ANSI escapes (calling `with_ansi(true)`) requires the "ansi" + /// crate feature flag. Calling `with_ansi(true)` without the "ansi" + /// feature flag enabled will panic if debug assertions are enabled, or + /// print a warning otherwise. + /// + /// This method itself is still available without the feature flag. This + /// is to allow ANSI escape codes to be explicitly *disabled* without + /// having to opt-in to the dependencies required to emit ANSI formatting. + /// This way, code which constructs a formatter that should never emit + /// ANSI escape codes can ensure that they are not used, regardless of + /// whether or not other crates in the dependency graph enable the "ansi" + /// feature flag. pub fn with_ansi(self, ansi: bool) -> CollectorBuilder, F, W> { CollectorBuilder { inner: self.inner.with_ansi(ansi),