Crate consortium_log 

A tiny logging facade that forwards to defmt, tracing, both, or neither, chosen by Cargo features.

Consortium spans no_std firmware (which logs with defmt) and std host-side tooling such as the config codegen (which logs with tracing). This crate lets a single call site — consortium_log::trace!(...) — compile against whichever backend the consuming crate turns on:

• defmt routes each macro to the matching defmt macro.
• tracing routes each macro to the matching tracing macro. tracing also enables alloc because the tracing dependency needs it.
• With both enabled, every event is emitted to both backends.
• With neither enabled, the macros expand to nothing.

Format syntax

The portable subset is a format string plus positional arguments — trace!("channel {} lowered", name) — or Rust-style implicit captures — trace!("channel {name} lowered"). Implicit captures are normalized to indexed arguments before being forwarded, because defmt does not parse them itself. Each argument must implement the traits both backends require (defmt::Format for defmt, core::fmt::Display/Debug for tracing). Backend-specific extensions (defmt’s {=u8} type hints, tracing’s structured fields) are only valid when that backend is the sole one enabled.

Log arguments must be side-effect free: when no backend is enabled the macros expand to nothing and the arguments are never evaluated.

Features

• defmt — forward to the defmt logging macros. No direct defmt dependency is needed at the call site: this crate re-exports defmt (the re-export exists only when the feature is on, so it is not linked here) and the dispatch macro binds it into scope for the expansion.
• tracing — forward to the tracing logging macros (implies alloc). tracing’s macros are $crate-hygienic, so no direct dependency is needed beyond this crate.
• alloc — marker capability required by tracing; enabling it alone pulls no backend.

Neither backend leaks its name into the call site, so enabling one on this crate alone resolves. That matters under Cargo feature unification: one workspace member turning on consortium-log/defmt switches the facade for every member sharing the build, including ones whose own defmt feature is off and which therefore have no defmt in their extern prelude.

Names are only half of it, though. With the defmt backend live, every logged argument needs a defmt::Format impl, and a crate that gates its impls on its own defmt feature will not have emitted them — foreign types such as anyhow::Error cannot have them at all. Gate those impls with when_defmt! so they track the backend, and, for the types that can never implement it, keep consortium-log/defmt out of any default feature so a host build never switches the backend on by accident.

Macros

debug

Logs at the debug level to every enabled backend.

error

Logs at the error level to every enabled backend.

info

Logs at the info level to every enabled backend.

trace

Logs at the trace level to every enabled backend. See the crate docs for the portable format syntax.

warn

Logs at the warn level to every enabled backend.

when_defmt

Drops the items it wraps, because this crate’s defmt backend is disabled.