Make logging filters work again by moving EnvFilter into its own layer #147613
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`tracing` at the time of writing has a feature (?) in its Filter implementation, so that filters like EnvFilter are consulted for status of a span or event and whether it is marked as interesting for logging. Combining a Filter with another layer through the `with_filter` combinator produces a filtered layer that enables an event unless it is statically determined that the event is uninteresting. However, if the filter is dynamic, because of filtering on span names or field values as an example, events are **always** enabled. There is an `event_enabled` predicate on `EnvFilter` implementation but it falls back to default and, thus, the dynamic filters are **unused**. This patch re-enables span- and field-based filters.
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rustbot has assigned @jdonszelmann. Use |
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this seems useful, @bors r+ rollup |
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Oct 13, 2025
…r=jdonszelmann Make logging filters work again by moving EnvFilter into its own layer `tracing` at the time of writing has a feature (?) in its Filter implementation, so that filters like EnvFilter are consulted for status of a span or event and whether it is marked as interesting for logging. Combining a Filter with another layer through the `with_filter` combinator produces a filtered layer that enables an event unless it is statically determined that the event is uninteresting. However, if the filter is dynamic, because of filtering on span names or field values as an example, events are **always** enabled by design. There is an `event_enabled` predicate on `EnvFilter` implementation but it falls back to default and, thus, the dynamic filters are **unused**. Previously, `RUSTC_LOG=[]` or `RUSTC_LOG=[garbage]` enables all events, even when spans do not match. This patch re-enables span- and field-based filters. With `RUSTC_LOG=[garbage]` one should expect no events are enabled again. This will help with development greatly because we can meaningfully filter internal logs again.
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Cc @Stypox -- I hope this doesn't break the Miri profiling logic. |
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tracingat the time of writing has a feature (?) in its Filter implementation, so that filters like EnvFilter are consulted for status of a span or event and whether it is marked as interesting for logging. Combining a Filter with another layer through thewith_filtercombinator produces a filtered layer that enables an event unless it is statically determined that the event is uninteresting. However, if the filter is dynamic, because of filtering on span names or field values as an example, events are always enabled by design. There is anevent_enabledpredicate onEnvFilterimplementation but it falls back to default and, thus, the dynamic filters are unused.Previously,
RUSTC_LOG=[]orRUSTC_LOG=[garbage]enables all events, even when spans do not match.This patch re-enables span- and field-based filters. With
RUSTC_LOG=[garbage]one should expect no events are enabled again. This will help with development greatly because we can meaningfully filter internal logs again.