tracing, core: re-implement empty fields #548
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Right now, there is no way to indicate that a span field _currently_ has no value but that a value will be recorded later. Tracing used to support this concept, but when we added local-variable shorthand, it was removed from the macros, as we needed to use the previous syntax for indicating empty fields for local variable shorthand. See #77 for details. This commit side-steps the problem of determining an appropriate _syntax_ for empty fields by adding a special value _type_, called `Empty`. Now, empty values can be indicated like ```rust span!("my_span", foo = 5, bar = tracing::field::Empty); ``` The `Empty` type implements `Value`, but its' `record` method is a no-op that doesn't' call any functions on the visitor. Therefore, when a field is empty, the visitor will not see it. An empty field can then be recorded later using `Subscriber::record` (or the corresponding `Span` method in `tracing`). Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw
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davidbarsky
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Jan 29, 2020
| /// // ... | ||
| /// | ||
| /// // Now, record a value for parting as well. | ||
| /// span.record("parting", &"goodbye world!"); |
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Since "parting" needs to referenced as a string, I'd add a comment noting that difference between macros and normal function parameters as it took me a few seconds to parse the example in https://deploy-preview-548--tracing-rs.netlify.com/tracing/span/struct.span?search=#method.record.
davidbarsky
reviewed
Jan 29, 2020
Comment on lines
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| //! // Now, record a value for parting as well. | ||
| //! span.record("parting", &"goodbye world!"); |
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Same comment as I mentioned prior would be handy here too.
davidbarsky
approved these changes
Jan 29, 2020
|
@tokio-rs/tracing does anyone else want to weigh in on this before I merge it? |
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw
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Feb 24, 2020
Added: - `field::Empty` type for declaring empty fields whose values will be recorded later (#548) - `field::Value` implementations for `Wrapping` and `NonZero*` numbers (#538) Fixed: - Broken and unresolvable links in RustDoc (#595) Thanks to @oli-cosmian for contributing to this release! Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw
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Feb 24, 2020
### Added - `field::Empty` type for declaring empty fields whose values will be recorded later (#548) - `field::Value` implementations for `Wrapping` and `NonZero*` numbers (#538) ### Fixed - Broken and unresolvable links in RustDoc (#595) Thanks to @oli-cosmian for contributing to this release! Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw
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Feb 26, 2020
Added: - **field**: `field::Empty` type for declaring empty fields whose values will be recorded later (#548) - **field**: `field::Value` implementations for `Wrapping` and `NonZero*` numbers (#538) - **attributes**: Support for adding arbitrary literal fields to spans generated by `#[instrument]` (#569) - **attributes**: `#[instrument]` now emits a helpful compiler error when attempting to skip a function parameter (#600) Changed: - **attributes**: The `#[instrument]` attribute was placed under an on-by-default feature flag "attributes" (#603) Fixed: - Broken and unresolvable links in RustDoc (#595) Thanks to @oli-cosmian and @Kobzol for contributing to this release! Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw
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Feb 27, 2020
### Added - **field**: `field::Empty` type for declaring empty fields whose values will be recorded later (#548) - **field**: `field::Value` implementations for `Wrapping` and `NonZero*` numbers (#538) - **attributes**: Support for adding arbitrary literal fields to spans generated by `#[instrument]` (#569) - **attributes**: `#[instrument]` now emits a helpful compiler error when attempting to skip a function parameter (#600) ### Changed - **attributes**: The `#[instrument]` attribute was placed under an on-by-default feature flag "attributes" (#603) ### Fixed - Broken and unresolvable links in RustDoc (#595) Thanks to @oli-cosmian and @Kobzol for contributing to this release! Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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Right now, there is no way to indicate that a span field currently
has no value but that a value will be recorded later. Tracing used to
support this concept, but when we added local-variable shorthand, it was
removed from the macros, as we needed to use the previous syntax for
indicating empty fields for local variable shorthand. See #77 for
details.
This commit side-steps the problem of determining an appropriate
syntax for empty fields by adding a special value type, called
Empty. Now, empty values can be indicated likeThe
Emptytype implementsValue, but its'recordmethod is a no-opthat doesn't' call any functions on the visitor. Therefore, when a field
is empty, the visitor will not see it. An empty field can then be
recorded later using
Subscriber::record(or the correspondingSpanmethod in
tracing).Closes #77
Signed-off-by: Eliza Weisman eliza@buoyant.io