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subscriber: feature flags that require std enable it #1660

Merged
merged 2 commits into from
Oct 20, 2021
Merged

subscriber: feature flags that require std enable it #1660

merged 2 commits into from
Oct 20, 2021

Commits on Oct 20, 2021

  1. subscriber: feature flags that require std enable it 

    ## Motivation

Currently, some `tracing-subscriber` dependencies in other crates use
`default-features = false`, to ensure that unneeded default features of
`tracing-subscriber` are not inadvertently enabled. However, some of the
features those crates enable also require the `std` feature flag. The
`default-features = false` config _disables_ the `std` feature, so the
required features are not available.

## Solution

This branch changes `tracing-subscriber`'s `fmt`, `registry`, and
`env-filter` feature flags to also enable the `std` feature flag
automatically.

## Alternatives

As an alternative solution, we could change crates that depend on
`tracing-subscriber` with `default-features = false` to also explicitly
ensure that the `std` feature is enabled (which might be worth doing
regardless). This is what PR #1659 does. However, I think the approach
in this branch is more correct; the feature flags that require standard
library support should automatically enable it. This provides a better
experience for most users, who are simply adding `default-features = false`
in order to avoid enabling un-needed features, not to support
`no_std`, and would like enabling a feature flag to *actually* enable
that feature.

`no_std` users will know not to enable `registry`, `fmt`, and
`env-filter` because the documentation notes that those features require
the standard library.
    @hawkw
    hawkw committed Oct 20, 2021
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  2. Merge branch 'master' into eliza/features-require-std

    @hawkw
    hawkw authored Oct 20, 2021
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