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Nanaloveyuki
82 lines
2.4 KiB
Markdown
82 lines
2.4 KiB
Markdown
---
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name: logger-trace
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group: api
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category: logging
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update-time: 20260512
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description: Emit a trace-level record through the logger using the lowest built-in severity shortcut.
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key-word:
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- logger
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- trace
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- sync
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- public
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---
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## Logger-trace
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Emit a trace-level record through the synchronous logger. This is the convenience wrapper for `log(Level::Trace, ...)`.
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### Interface
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```moonbit
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pub fn[S : Sink] Logger::trace(self : Logger[S], message : String, fields~ : Array[Field] = []) -> Unit {}
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```
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#### input
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- `self : Logger[S]` - Logger that should emit the trace record.
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- `message : String` - Trace message text.
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- `fields : Array[Field]` - Optional structured fields attached to the record.
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#### output
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- `Unit` - No return value. The record is handled according to the logger threshold and sink pipeline.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- This helper delegates to `log(Level::Trace, ...)`.
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- Trace is the lowest built-in severity and is often disabled in production.
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- This helper does not accept a per-call target override. It uses the logger's stored target unless the logger was derived earlier with `with_target(...)` or `child(...)`.
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- Context, filtering, patching, and queue wrappers still apply through the logger sink chain.
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### How to Use
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Here are some specific examples provided.
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#### When Need Low-level Execution Tracing
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When fine-grained flow diagnostics are useful:
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```moonbit
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logger.trace("entered reconciliation step")
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```
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In this example, trace intent is explicit and concise.
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#### When Attach Structured Trace Context
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When a trace event should include fields:
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```moonbit
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logger.trace("cache probe", fields=[field("key", "user:42")])
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```
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In this example, trace output stays lightweight while still carrying structured detail.
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And any shared context already carried by the logger still participates through the sink pipeline.
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The write still uses the logger's stored target because this shortcut does not take a one-off `target=` override.
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### Error Case
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e.g.:
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- If the logger minimum level is above `Trace`, the call returns without writing a record.
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- If a per-call target override is required, this helper is too narrow and `log(...)` should be used instead.
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### Notes
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1. Prefer this helper when trace intent is clearer than a raw `log(Level::Trace, ...)` call.
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2. Very verbose trace logging can become expensive even in a synchronous pipeline.
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