Add Effect.whenLogLevel (#4342)

Author: indietyp

.changeset/dirty-ways-dress.md

@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+Add `Effect.whenLogLevel`, which conditionally executes an effect if the specified log level is enabled

packages/effect/src/Effect.ts

@@ -40,7 +40,7 @@ import * as runtime_ from "./internal/runtime.js"
 import * as schedule_ from "./internal/schedule.js"
 import * as internalTracer from "./internal/tracer.js"
 import type * as Layer from "./Layer.js"
-import type { LogLevel } from "./LogLevel.js"
+import type * as LogLevel from "./LogLevel.js"
 import type * as ManagedRuntime from "./ManagedRuntime.js"
 import type * as Metric from "./Metric.js"
 import type * as MetricLabel from "./MetricLabel.js"
@@ -10678,7 +10678,7 @@ export const log: (...message: ReadonlyArray<any>) => Effect<void, never, never>
  * @category Logging
  */
 export const logWithLevel = (
-  level: LogLevel,
+  level: LogLevel.LogLevel,
   ...message: ReadonlyArray<any>
 ): Effect<void> => effect.logWithLevel(level)(...message)
 
@@ -10972,10 +10972,46 @@ export const logAnnotations: Effect<HashMap.HashMap<string, unknown>> = effect.l
  * @category Logging
  */
 export const withUnhandledErrorLogLevel: {
-  (level: Option.Option<LogLevel>): <A, E, R>(self: Effect<A, E, R>) => Effect<A, E, R>
-  <A, E, R>(self: Effect<A, E, R>, level: Option.Option<LogLevel>): Effect<A, E, R>
+  (level: Option.Option<LogLevel.LogLevel>): <A, E, R>(self: Effect<A, E, R>) => Effect<A, E, R>
+  <A, E, R>(self: Effect<A, E, R>, level: Option.Option<LogLevel.LogLevel>): Effect<A, E, R>
 } = core.withUnhandledErrorLogLevel
 
+/**
+ * Conditionally executes an effect based on the specified log level and currently enabled log level.
+ *
+ * **Details**
+ *
+ * This function runs the provided effect only if the specified log level is
+ * enabled. If the log level is enabled, the effect is executed and its result
+ * is wrapped in `Some`. If the log level is not enabled, the effect is not
+ * executed and `None` is returned.
+ *
+ * This function is useful for conditionally executing logging-related effects
+ * or other operations that depend on the current log level configuration.
+ *
+ * @example
+ * ```ts
+ * import { Effect, Logger, LogLevel } from "effect"
+ *
+ * const program = Effect.gen(function* () {
+ *   yield* Effect.whenLogLevel(Effect.logTrace("message1"), LogLevel.Trace); // returns `None`
+ *   yield* Effect.whenLogLevel(Effect.logDebug("message2"), LogLevel.Debug); // returns `Some`
+ * }).pipe(Logger.withMinimumLogLevel(LogLevel.Debug));
+ *
+ * // Effect.runFork(program)
+ * // timestamp=... level=DEBUG fiber=#0 message=message2
+ * ```
+ *
+ * @see {@link FiberRef.minimumLogLevel} to retrieve the current minimum log level.
+ *
+ * @since 3.13.0
+ * @category Logging
+ */
+export const whenLogLevel: {
+  (level: LogLevel.LogLevel | LogLevel.Literal): <A, E, R>(self: Effect<A, E, R>) => Effect<Option.Option<A>, E, R>
+  <A, E, R>(self: Effect<A, E, R>, level: LogLevel.LogLevel | LogLevel.Literal): Effect<Option.Option<A>, E, R>
+} = fiberRuntime.whenLogLevel
+
 /**
  * Converts an effect's failure into a fiber termination, removing the error
  * from the effect's type.

packages/effect/src/internal/fiberRuntime.ts

@@ -1631,6 +1631,30 @@ export const annotateLogsScoped: {
   )
 }
 
+/** @internal */
+export const whenLogLevel = dual<
+  (
+    level: LogLevel.LogLevel | LogLevel.Literal
+  ) => <A, E, R>(effect: Effect.Effect<A, E, R>) => Effect.Effect<Option.Option<A>, E, R>,
+  <A, E, R>(
+    effect: Effect.Effect<A, E, R>,
+    level: LogLevel.LogLevel | LogLevel.Literal
+  ) => Effect.Effect<Option.Option<A>, E, R>
+>(2, (effect, level) => {
+  const requiredLogLevel = typeof level === "string" ? LogLevel.fromLiteral(level) : level
+
+  return core.withFiberRuntime((fiberState) => {
+    const minimumLogLevel = fiberState.getFiberRef(currentMinimumLogLevel)
+
+    // Imitate the behaviour of `FiberRuntime.log`
+    if (LogLevel.greaterThan(minimumLogLevel, requiredLogLevel)) {
+      return core.succeed(Option.none())
+    }
+
+    return core.map(effect, Option.some)
+  })
+})
+
 // circular with Effect
 
 /* @internal */