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Nanaloveyuki
90 lines
2.9 KiB
Markdown
90 lines
2.9 KiB
Markdown
---
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name: library-logger-warn
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group: api
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category: facade
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update-time: 20260613
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description: Emit a warn-level record through a LibraryLogger facade by delegating to the wrapped logger's warn shortcut.
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key-word:
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- library
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- facade
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- warn
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- public
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---
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## Library-logger-warn
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Emit a warn-level record through the library-facing sync logger. This is the convenience wrapper for `log(Level::Warn, ...)` on `LibraryLogger[S]`.
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### Interface
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```moonbit
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pub fn[S : Sink] LibraryLogger::warn(
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self : LibraryLogger[S],
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message : String,
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fields~ : Array[Field] = [],
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) -> Unit {
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```
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#### input
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- `self : LibraryLogger[S]` - Library-facing logger that should emit the warning record.
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- `message : String` - Warning 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 current threshold and wrapped 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 `warn(...)` on the wrapped logger, which in turn uses `log(Level::Warn, ...)`.
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- Warning records are useful for abnormal but non-fatal conditions.
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- This helper does not accept a per-call target override. It uses the facade's stored target unless the facade was derived earlier with `with_target(...)` or `child(...)`.
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- All sink-side wrappers still participate normally in the write path.
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- Broader composition helpers remain on the underlying `Logger[S]` and require `to_logger()` first.
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### How to Use
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Here are some specific examples provided.
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#### When Signal A Recoverable Library Problem
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When an operation degraded but still continued:
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```moonbit
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logger.warn("cache miss ratio increased")
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```
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In this example, the event is elevated above normal information without being treated as a hard failure.
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#### When Attach Structured Warning Context
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When a warning should include machine-readable detail:
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```moonbit
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logger.warn("retry scheduled", fields=[field("attempt", "3")])
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```
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In this example, the warning remains easy to filter and inspect later.
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And any shared context already carried by the facade still participates through the wrapped logger pipeline.
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And the write still uses the facade'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 `Warn`, the call returns without writing a record.
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- If a target override is needed at this call site, use `log(...)` instead of this shortcut.
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- If callers need broader composition helpers after logging, they must unwrap first with `to_logger()`.
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### Notes
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1. Use this helper for degraded or suspicious states that do not stop execution.
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2. Warning logs are often a practical signal threshold for alerting or separate routing.
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3. Use `log(...)` instead when the call site needs a per-call target override or a dynamic level.
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