📝 Document logger composition APIs

docs/api/logger-with-timestamp.md

@@ -0,0 +1,101 @@
+---
+name: logger-with-timestamp
+group: api
+category: logging
+update-time: 20260512
+description: Enable or disable automatic timestamp capture for records emitted by a logger.
+key-word:
+    - logger
+    - timestamp
+    - record
+    - public
+---
+
+## Logger-with-timestamp
+
+Enable or disable automatic timestamp capture on log emission. This API controls whether `Logger::log(...)` records the current time through `@env.now()` or leaves the timestamp at `0UL`.
+
+### Interface
+
+```moonbit
+pub fn[S] Logger::with_timestamp(self : Logger[S], enabled~ : Bool = true) -> Logger[S] {}
+```
+
+#### input
+
+- `self : Logger[S]` - Base logger whose timestamp behavior should change.
+- `enabled : Bool` - Whether emitted records should capture current time automatically.
+
+#### output
+
+- `Logger[S]` - A new logger value with updated timestamp behavior.
+
+---
+
+e.g.:
+```moonbit
+pub fn[S] Logger::with_timestamp(self : Logger[S], enabled~ : Bool = true) -> Logger[S] {}
+```
+
+#### input
+
+- `self : Logger[S]` - Current logger.
+- `enabled : Bool` - Timestamp toggle.
+
+#### output
+
+- `Logger[S]` - Logger with updated timestamp behavior.
+
+---
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- When enabled, `log(...)` captures `@env.now()` and stores it in the record.
+- When disabled, emitted records use `0UL` as the timestamp value.
+- This setting affects later emitted records only.
+- Formatter or sink behavior stays unchanged; they just receive records with or without real timestamps.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Real Event Time In Records
+
+When downstream formatting or JSON output should include event time:
+```moonbit
+let logger = Logger::new(console_sink())
+  .with_timestamp()
+```
+
+In this example, each emitted record captures current time automatically.
+
+#### When Need Deterministic Or Minimal Records
+
+When timestamps should be disabled for tests or reduced output:
+```moonbit
+let logger = Logger::new(console_sink())
+  .with_timestamp(enabled=false)
+```
+
+In this example, records are emitted without runtime time capture.
+
+### Error Case
+
+e.g.:
+- If timestamps are disabled, formatters that expect meaningful time values may show empty or zero-like timestamp output.
+
+- If callers need timestamps only for one record, per-call customization is not provided here and a separate logger value may be clearer.
+
+### Notes
+
+Notes are here.
+
+1. This API controls record creation, not formatter display policy.
+
+2. It works well together with text formatters that optionally show timestamps.
+
+3. The helper is useful for tests, deterministic snapshots, and production timing.
+
+4. The returned logger preserves the same sink, target, and min level settings.