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## Motivation In PR #672, the `#[instrument]` attribute was rewritten to use a custom `syn` parser rather than using `syn::AttributeArgs`. This was primarily to allow the use of arbitrary expressions as fields, but it had the side benefit of also allowing more sophisticated error reporting. In particular, we were able to replace the previous behavior of silently ignoring unknown input with a compiler error, which has been requested a few times (see #772 and #727). However, emitting a compiler error for inputs that we previously allowed (even if they did nothing) is technically a breaking change --- see https://github.com/tokio-rs/tracing/pull/773#issuecomment-652052525 and following comments. This means that the other new features added in #672 cannot be released until we release `tracing-subscriber` 0.2. ## Solution This branch avoids the breaking change by downgrading these errors to warnings. However, it isn't currently possible to emit a warning from a proc-macro on stable --- the `proc_macro::Diagnostic` API which would allow this requires a nightly feature. This branch hacks around this by generating a fake deprecated item with for each unrecognized token in the input, emitting the skipped item's parse error as the deprecation's `note`, and "using" the deprecated item. The deprecated warning is used here rather than other code that will emit compiler warnings, because it gives us a way to customize the warning output (via the `note` field). I've tried to make it fairly obvious that this is not a "real" deprecation. Sample output looks like this:  Fixes #727 Fixes #772 Signed-off-by: Eliza Weisman <eliza@elizas.website>
tracing-attributes
Macro attributes for application-level tracing.
Overview
tracing is a framework for instrumenting Rust programs to collect
structured, event-based diagnostic information. This crate provides the
#[instrument] attribute for automatically instrumenting functions using
tracing.
Note that this macro is also re-exported by the main tracing crate.
Usage
First, add this to your Cargo.toml:
[dependencies]
tracing-attributes = "0.1.8"
Compiler support: requires rustc 1.39+
This crate provides the #[instrument] attribute for instrumenting a function
with a tracing span. For example:
use tracing_attributes::instrument;
#[instrument]
pub fn my_function(my_arg: usize) {
// ...
}
License
This project is licensed under the MIT license.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tokio by you, shall be licensed as MIT, without any additional terms or conditions.