Module debug 

Debug logging helpers used by Hotaru internals. Debug logging module for development-time diagnostics.

Provides conditional compilation macros that enable detailed logging during development while ensuring zero runtime overhead in production builds. All macros are controlled by the dev-log feature flag.

Three-arm design (dev-log × std / embedded)

Each macro has three cfg-arms so no build ever pulls in std machinery it doesn’t want:

dev-log	std / embedded	Expansion
off	either	nothing — arguments are not evaluated.
on	std	println! / eprintln! with [LEVEL] prefix (the classic behaviour).
on	embedded	Hollow expansion — let _ = core::format_args!(...). Arguments are still evaluated so unused_variables warnings at call sites stay quiet, but no formatting, allocation, or IO happens.

The hollow embedded arm exists because embedded builds are #![no_std] — println! / eprintln! are gone, and format! allocates via alloc (which is available but wasteful for a no-op). format_args! is core:: and creates a stack-only core::fmt::Arguments value at zero allocation cost. Wrapping in let _ = ...; marks the resulting value as intentionally discarded.

Future: hooking a real embedded logger

When HCR picks an embedded logger (defmt / semihosting / RTT / the log crate), route the hollow arm through a user-installed sink function — the macro body changes, call sites don’t. Design sketch: a static LOGGER: OnceCell<fn(core::fmt::Arguments<'_>)> that the user’s #[entry] installs once, and the embedded arm calls it if present. Deferred until an actual logger is chosen.

Usage

Enable the feature in your Cargo.toml or via command line:

cargo run --features "dev-log"

Then import and use the macros:

use hotaru_core::{debug_log, debug_error};
debug_log!("Server started on port {}", 8080);
debug_error!("Connection failed: {}", err);