CallSiteIrTransformer

Rewrites every call to a log4k logging entry point so the emitted event carries a compile-time io.github.smyrgeorge.log4k.SourceLocation — the call's file, line, and enclosing function. Because the values are baked in as constants, accurate source locations cost no runtime stack-walking, and work uniformly on every Kotlin target (including Native, JS, and Wasm, where walking the stack is expensive or impossible).

Intercepted entry points, and how each is rewritten:

• Logger.log(level, span, tags, message, arguments, throwable) — retargeted to the overload with the trailing callSite parameter, all other arguments copied verbatim.

• Logger.at(level) { … } and the atTrace/…/atError shorthands — retargeted to at(level, callSite, f); the builder lambda stays in inline position, so its laziness (and any non-local returns inside it) are preserved.

• The level-named trace/debug/info/warn/error(…) forwarders — the classic extensions (log4k-classic), the context-aware overloads (log4k-context, context(TracingContext) / context(Span)), and the log.classic.… escape hatch (Log4kClassic) — remapped directly onto Logger.log(…, callSite). They are all trivial forwarders, so the plugin re-derives the mapping from the callee's signature instead of hardcoding each shape: the level comes from the function name, every value parameter is classified by its type (Span / Tags / String message / () -> String lazy message / Throwable / vararg arguments), a Log4kClassic receiver is unwrapped through its logger property, and a context parameter contributes the span (a Span directly; a TracingContext via currentOrNull()). Argument expressions are evaluated into temporaries in their original order, so side-effect ordering is unchanged. A lazy { … } message lambda is invoked behind an isEnabled(level) guard — mirroring the level gate the original inline extension compiled to — so a disabled logger still costs neither the message building nor the lambda allocation.

A call is left untouched (keeping a null call site, never breaking compilation) when:

• A classic lazy-message lambda contains a non-local jump — a return, break, or continue targeting an enclosing function or loop (it cannot be moved behind the guard);

• The callee's shape is not recognized (e.g., a future log4k adds a parameter this plugin predates);

• The call has no source offsets (synthetic code).