Feature request: Ineffective .with_regex(false) when parsing in EnvFilter::builder in build

[SajjadPourali]

tracing/tracing-subscriber/src/filter/env/directive.rs

Line 122 in bf05c61

pub(super) fn parse(from: &str, regex: bool) -> Result<Self, ParseError> {

The parse method internally calls all the methods of EnvFilter::builder, and since it checks the regex during runtime, its dependency will remain in the code.

    let cmd = EnvFilter::builder()
        .with_regex(false)
        .with_default_directive(LevelFilter::INFO.into())
        .parse(var)
        .unwrap();

 File  .text     Size Crate
 7.5%  25.1% 326.6KiB std
 4.1%  13.7% 177.5KiB regex_automata
 2.9%   9.7% 125.4KiB [Unknown]
 2.3%   7.7%  99.9KiB regex_syntax
 1.6%   5.3%  68.3KiB ...
....

tracing-subscriber = "0.3.17"

It would be really nice to have a feature to disable it during code compilation to reduce the binary size.

[hawkw]

with_regex(false) simply disables the support for matching regular expressions in the filter. However, env_filter also uses regular expressions to parse the filter from an input string, so EnvFilter would not be available at all without a regex dependency.

If you're concerned about the binary size impact of regex, and you're not relying on EnvFilter features like matching on field values, you may want to consider using the Targets filter instead. Targets implements a subset of the filtering syntax supported by EnvFilter: it can match on events and spans based on their target/module path.

Essentially, the Targets filter implements the parts of EnvFilter that can easily be implemented without a dependency on regex. So, in a sense, the feature flag for disabling regex already exists: just disable the env_filter feature and use the Targets filter, instead.

Hope that's helpful!

[SajjadPourali]

Perfect, that's exactly what I was looking for.