4dff740ebd
There's currently no way to get the registered directives from a
`Targets` instance, which is a barrier to some use-cases such as
combining user-supplied directives with application-supplied defaults.
This commit adds a `Targets::targets` method, which returns an iterator
of `(&str, LevelFilter)` pairs, one for each directive (excluding the
default level, whose `target` is `None`).
Items are yielded as per the underlying `DirectiveSet::directives`,
which would yield itms in specifity order (as constructed by
`DirectiveSet::add`). However, the order has been left explicitly
undefined in the documentation for `Targets::targets` on the basis that
this is an implementation detail that may change.
## Motivation
As hinted in the commit message, my use-case is to have an
application-supplied 'base' `Targets` filter, which can then be
extended/overridden by a user-supplied filter parsed from `RUST_LOG`
(e.g.).
Sadly, there's currently no way of getting the directives out of a
`Targets` instance, nor to re-serialize to the string representation.
Thus, the only way to implement the above would be to manually parse the
user-supplied filters in the application, which is shame since it
duplicates the implementation here and would be prone to drift/subtle
incompatibilities.
## Solution
The proposed solution is to add methods to `Targets` to retrieve the
underlying directives.
```rust
// application-defined defaults, for a useful level of information
let mut filter = Targets::new()
.with_target("my_crate", LevelFilter::INFO)
.with_target("important_dependency", LevelFilter::INFO);
if let Ok(overrides) = std::env::var("RUST_LOG") {
let overrides: Targets = overrides.parse().unwrap();
// merge user-supplied overrides, which can enable additional tracing
// or disable default tracing
filter.extend(overrides.iter());
// ^^^^^^^^^ this is new
}
```
For this PR, I've gone for `fn iter(&self) -> Iter`, e.g. a method
`targets` that returns an iterator over the pairs of `(&str,
LevelFilter)` in the underlying directives. The iterator excludes any
default level(s) where `target` would be `None`. This matches nicely
with the `FromIterator` and `Extend` impls, which use `(impl
Into<String>, impl Into<LevelFilter>)`.
In addition, I've added `IntoIterator` implementations for `&Targets`
and for `Targets`. The by-value `IntoIterator` implementation returns an
`IntoIter` type that moves the targets as `String`s, rather than as
borrowed `&str`s. This makes `extend` more efficient when moving a
second `Targets` by value.
tracing-subscriber
Utilities for implementing and composing tracing subscribers.
Compiler support: requires rustc 1.42+
Supported Rust Versions
Tracing is built against the latest stable release. The minimum supported version is 1.42. The current Tracing version is not guaranteed to build on Rust versions earlier than the minimum supported version.
Tracing follows the same compiler support policies as the rest of the Tokio project. The current stable Rust compiler and the three most recent minor versions before it will always be supported. For example, if the current stable compiler version is 1.45, the minimum supported version will not be increased past 1.42, three minor versions prior. Increasing the minimum supported compiler version is not considered a semver breaking change as long as doing so complies with this policy.
License
This project is licensed under the MIT license.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tracing by you, shall be licensed as MIT, without any additional terms or conditions.