macros: Handle constant field names #2617

wyfo · 2023-06-15T16:23:15Z

Motivation

I've found myself in the case where I wanted to have customized event field name for different trait implementations. In fact, these implementations are completely unrelated (in separate applications), so, in this use case, I find more readable to have foo="some_id" and bar=16 instead of resource="foo" value="some_id" and resource=bar value=16

Because events only accept identifier or literal as field name, this is quite cumbersome/impossible to do. A simple solution could be to make events accept constant expression too; in my use case, I could then add a associated constant to my trait.

Solution

This PR proposes a new syntax for using constant field names:

tracing::debug!({ CONSTANT_EXPR } = "foo");

This is the same syntax than constant expression, so it should be quite intuitive.

To avoid constant expression names conflict, internal variables of macro expansion have been prefixed with __, e.g. __CALLSITE.

hawkw

Thanks! I'm definitely open to adding this. It would be nice to add tests for a few more cases, if you don't mind?

We may also want to allow constants to be used as span names and/or targets for spans and events, but we could look into this in a follow-up PR.

tracing/src/lib.rs

hawkw · 2023-06-15T17:19:51Z

tracing/tests/event.rs

+        .run_with_handle();
+    with_default(collector, || {
+        const FOO: &str = "foo";
+        tracing::event!(Level::INFO, { FOO } = "bar");


can we also add a test which mixes constant and non-constant field names? i'd like to ensure that the macro parses unambiguously when the two forms are mixed.

we may also want to test constant field names that are not in the curren scope, like { some_module::FOO } and { some_module::SomeType::FOO }?

hawkw · 2023-06-15T17:20:15Z

tracing/tests/span.rs

+        .run_with_handle();
+    with_default(collector, || {
+        const FOO: &str = "foo";
+        tracing::span!(Level::TRACE, "my_span", { FOO } = "bar");


similarly, let's also test some spans with mixed constant and ident field names

Co-authored-by: Eliza Weisman <eliza@buoyant.io>

wyfo · 2023-06-22T07:42:58Z

Sorry for the delay, hard to find time for open-source at this moment...
I've updated the tests, it's indeed better now.

We may also want to allow constants to be used as span names and/or targets for spans and events, but we could look into this in a follow-up PR.

Actually, it's already possible, because they are all expr designators;

tracing::span!(std::convert::identity(tracing::Level::INFO), stringify!(my_span))

works fine for example.
On the other hand, an additional syntax was needed for fields because they use ident designator by default.

hawkw

this looks good to me, thank you! i had one suggestion for making the documentation a little bit more obvious.

tracing/src/lib.rs

hawkw · 2023-09-05T21:12:45Z

tracing/tests/event.rs

+        tracing::event!(
+            Level::INFO,
+            { std::convert::identity(FOO) } = "bar",
+            { "constant string" } = "also works",
+            foo.bar = "baz",
+            "quux"
+        );
+        tracing::event!(
+            Level::INFO,
+            {
+                { std::convert::identity(FOO) } = "bar",
+                { "constant string" } = "also works",
+                foo.bar = "baz",
+            },
+            "quux"
+        );


thanks for testing all these cases!

stormshield-frb · 2023-09-14T08:27:38Z

Hi. Great useful feature, thanks !!

While testing it out, I've noticed that it seems to work only for the tracing::event! and tracing::span! macro. Is there any plan to integrate this feature with the #[instrument] macro and all the other 'classic' macros (debug, info, warn, etc) ? Thanks

I've found myself in the case where I wanted to have customized event field name for different trait implementations. In fact, these implementations are completely unrelated (in separate applications), so, in this use case, I find more readable to have `foo="some_id"` and `bar=16` instead of `resource="foo" value="some_id"` and `resource=bar value=16` Because events only accept identifier or literal as field name, this is quite cumbersome/impossible to do. A simple solution could be to make events accept constant expression too; in my use case, I could then add a associated constant to my trait. This PR proposes a new syntax for using constant field names: ```rust tracing::debug!({ CONSTANT_EXPR } = "foo"); ``` This is the same syntax than constant expression, so it should be quite intuitive. To avoid constant expression names conflict, internal variables of macro expansion have been prefixed with `__`, e.g. `__CALLSITE`. Co-authored-by: Joseph Perez <joseph.perez@numberly.com> Co-authored-by: Eliza Weisman <eliza@buoyant.io>

# 0.1.39 (October 12, 2023) This release adds several additional features to the `tracing` macros. In addition, it updates the `tracing-core` dependency to [v0.1.32][core-0.1.32] and the `tracing-attributes` dependency to [v0.1.27][attrs-0.1.27]. ### Added - Allow constant field names in macros ([#2617]) - Allow setting event names in macros ([#2699]) - **core**: Allow `ValueSet`s of any length ([#2508]) ### Changed - `tracing-attributes`: updated to [0.1.27][attrs-0.1.27] - `tracing-core`: updated to [0.1.32][core-0.1.32] - **attributes**: Bump minimum version of proc-macro2 to 1.0.60 ([#2732]) - **attributes**: Generate less dead code for async block return type hint ([#2709]) ### Fixed - Use fully qualified names in macros for items exported from std prelude ([#2621], [#2757]) - **attributes**: Allow [`clippy::let_with_type_underscore`] in macro-generated code ([#2609]) - **attributes**: Allow `unknown_lints` in macro-generated code ([#2626]) - **attributes**: Fix a compilation error in `#[instrument]` when the `"log"` feature is enabled ([#2599]) ### Documented - Add `axum-insights` to relevant crates. ([#2713]) - Fix link to RAI pattern crate documentation ([#2612]) - Fix docs typos and warnings ([#2581]) - Add `clippy-tracing` to related crates ([#2628]) - Add `tracing-cloudwatch` to related crates ([#2667]) - Fix deadlink to `tracing-etw` repo ([#2602]) [#2617]: #2617 [#2699]: #2699 [#2508]: #2508 [#2621]: #2621 [#2713]: #2713 [#2581]: #2581 [#2628]: #2628 [#2667]: #2667 [#2602]: #2602 [#2626]: #2626 [#2757]: #2757 [#2732]: #2732 [#2709]: #2709 [#2599]: #2599 [`let_with_type_underscore`]: http://rust-lang.github.io/rust-clippy/rust-1.70.0/index.html#let_with_type_underscore [attrs-0.1.27]: https://github.com/tokio-rs/tracing/releases/tag/tracing-attributes-0.1.27 [core-0.1.32]: https://github.com/tokio-rs/tracing/releases/tag/tracing-core-0.1.32

Joseph Perez added 2 commits June 15, 2023 17:19

macros: Handle constant field names

48495eb

Add documentation

a3cc393

wyfo requested review from hawkw, davidbarsky and a team as code owners June 15, 2023 16:23

hawkw reviewed Jun 15, 2023

View reviewed changes

wyfo and others added 2 commits June 22, 2023 09:17

doc: fix typo

38a7232

Co-authored-by: Eliza Weisman <eliza@buoyant.io>

macros: refine constant field names tests

8f3d935

hawkw approved these changes Sep 5, 2023

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expand doc comment

a680b4c

hawkw enabled auto-merge (squash) September 5, 2023 21:15

hawkw added 2 commits September 5, 2023 14:19

Merge branch 'master' into constant_field_name

cb5b499

rename callsite in new macro cases from tokio-rs#2699

5d65b45

hawkw mentioned this pull request Sep 5, 2023

tracing: allow constant field names in macros #2712

Open

rustfmt

5092c87

hawkw merged commit 245d607 into tokio-rs:master Sep 5, 2023
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davidbarsky mentioned this pull request Sep 26, 2023

chore: backport roughly a year's worth of changes #2728

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macros: Handle constant field names #2617

macros: Handle constant field names #2617

wyfo commented Jun 15, 2023

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hawkw Jun 15, 2023

hawkw Jun 15, 2023

wyfo commented Jun 22, 2023 •

edited

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stormshield-frb commented Sep 14, 2023

macros: Handle constant field names #2617

macros: Handle constant field names #2617

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wyfo commented Jun 15, 2023

Motivation

Solution

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wyfo commented Jun 22, 2023 • edited

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stormshield-frb commented Sep 14, 2023

wyfo commented Jun 22, 2023 •

edited