tracing-core: implement PartialEq, Eq for Metadata, FieldSet
#2229
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A `FieldSet` is equal to another `FieldSet` if they share the same callsite and fields (provided in the same order). This ensures that a `Field` applicable to one `FieldSet` is applicable to any equal `FieldSet`. A `Metadata` is equal to another `Metadata` if all of their contained metadata is exactly equal.
hawkw
approved these changes
Jul 19, 2022
tracing-core/src/metadata.rs
Outdated
| @@ -57,6 +46,7 @@ use core::{ | |||
| /// [module path]: Self::module_path | |||
| /// [collector]: super::collect::Collect | |||
| /// [callsite identifier]: super::callsite::Identifier | |||
| #[derive(Eq, PartialEq)] | |||
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we may want a hand-written equality implementation for Metadatas so that we can compare the callsite identifier first, and short-circuit so that we don't have to do a bunch of string equality. i believe the derived PartialEq impl will compare fields in the order that they are declared.
that change could be made later as an optimization, though.
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actually, i believe the derived implementations also generate an implementation of the StructuralPartialEq trait, which allows matching a type as a match pattern (which is possible in v0.1.x of tracing-core, where Metadata's fields are pub). this means that a change from a hand-written implementation to a derived one is potentially a breaking change...
This change manually re-implements `PartialEq` and `Eq` for `Metadata` and `FieldSet` to define their equality strictly in terms of callsite equality. In debug builds, the equality of these types' other fields is also checked. Documentation is added to both `Metadata` and `FieldSet` explaining this behavior. The expectation that, in a well-behaving application, `Metadata` and `FieldSet`s with equal callsites will be otherwise equal is documented on `Callsite::metadata`. This is not a breaking change, as previous releases did not define equality for `Metadata` or `FieldSet`. The `Callsite` trait remains safe, as this expectation is not (yet) a safety-critical property.
|
@hawkw I went a little beyond your comments, and re-implemented |
hawkw
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Jul 19, 2022
hawkw
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A `FieldSet` is equal to another `FieldSet` if they share the same callsite and fields (provided in the same order). This ensures that a `Field` applicable to one `FieldSet` is applicable to any equal `FieldSet`. A `Metadata` is equal to another `Metadata` if all of their contained metadata is exactly equal. This change manually re-implements `PartialEq` and `Eq` for `Metadata` and `FieldSet` to define their equality strictly in terms of callsite equality. In debug builds, the equality of these types' other fields is also checked. Documentation is added to both `Metadata` and `FieldSet` explaining this behavior. The expectation that, in a well-behaving application, `Metadata` and `FieldSet`s with equal callsites will be otherwise equal is documented on `Callsite::metadata`. This is not a breaking change, as previous releases did not define equality for `Metadata` or `FieldSet`. The `Callsite` trait remains safe, as this expectation is not (yet) a safety-critical property.
hawkw
pushed a commit
that referenced
this pull request
Jul 20, 2022
A `FieldSet` is equal to another `FieldSet` if they share the same callsite and fields (provided in the same order). This ensures that a `Field` applicable to one `FieldSet` is applicable to any equal `FieldSet`. A `Metadata` is equal to another `Metadata` if all of their contained metadata is exactly equal. This change manually re-implements `PartialEq` and `Eq` for `Metadata` and `FieldSet` to define their equality strictly in terms of callsite equality. In debug builds, the equality of these types' other fields is also checked. Documentation is added to both `Metadata` and `FieldSet` explaining this behavior. The expectation that, in a well-behaving application, `Metadata` and `FieldSet`s with equal callsites will be otherwise equal is documented on `Callsite::metadata`. This is not a breaking change, as previous releases did not define equality for `Metadata` or `FieldSet`. The `Callsite` trait remains safe, as this expectation is not (yet) a safety-critical property.
hawkw
pushed a commit
that referenced
this pull request
Jul 20, 2022
A `FieldSet` is equal to another `FieldSet` if they share the same callsite and fields (provided in the same order). This ensures that a `Field` applicable to one `FieldSet` is applicable to any equal `FieldSet`. A `Metadata` is equal to another `Metadata` if all of their contained metadata is exactly equal. This change manually re-implements `PartialEq` and `Eq` for `Metadata` and `FieldSet` to define their equality strictly in terms of callsite equality. In debug builds, the equality of these types' other fields is also checked. Documentation is added to both `Metadata` and `FieldSet` explaining this behavior. The expectation that, in a well-behaving application, `Metadata` and `FieldSet`s with equal callsites will be otherwise equal is documented on `Callsite::metadata`. This is not a breaking change, as previous releases did not define equality for `Metadata` or `FieldSet`. The `Callsite` trait remains safe, as this expectation is not (yet) a safety-critical property.
This was referenced Jul 21, 2022
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hawkw
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Jul 29, 2022
# 0.1.29 (July 29, 2022) This release of `tracing-core` adds `PartialEq` and `Eq` implementations for metadata types, and improves error messages when setting the global default subscriber fails. ### Added - `PartialEq` and `Eq` implementations for `Metadata` ([#2229]) - `PartialEq` and `Eq` implementations for `FieldSet` ([#2229]) ### Fixed - Fixed unhelpful `fmt::Debug` output for `dispatcher::SetGlobalDefaultError` ([#2250]) - Fixed compilation with `-Z minimal-versions` ([#2246]) Thanks to @jswrenn and @CAD97 for contributing to this release! [#2229]: #2229 [#2246]: #2246 [#2250]: #2250
hawkw
added a commit
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this pull request
Jul 29, 2022
# 0.1.29 (July 29, 2022) This release of `tracing-core` adds `PartialEq` and `Eq` implementations for metadata types, and improves error messages when setting the global default subscriber fails. ### Added - `PartialEq` and `Eq` implementations for `Metadata` ([#2229]) - `PartialEq` and `Eq` implementations for `FieldSet` ([#2229]) ### Fixed - Fixed unhelpful `fmt::Debug` output for `dispatcher::SetGlobalDefaultError` ([#2250]) - Fixed compilation with `-Z minimal-versions` ([#2246]) Thanks to @jswrenn and @CAD97 for contributing to this release! [#2229]: #2229 [#2246]: #2246 [#2250]: #2250
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This change manually re-implements
PartialEqandEqforMetadataandFieldSetto define their equality strictly interms of callsite equality. In debug builds, the equality of
these types' other fields is also checked.
Documentation is added to both
MetadataandFieldSetexplaining this behavior. The expectation that, in a well-behaving
application,
MetadataandFieldSets with equal callsites will beotherwise equal is documented on
Callsite::metadata. This is nota breaking change, as previous releases did not define equality for
MetadataorFieldSet. TheCallsitetrait remains safe, as thisexpectation is not (yet) a safety-critical property.
This change improves the ergonomics of comparing
Metadata, whichis very useful for testing and user-facing examples.