v0.1.20 causes issues with Tonic

[jtescher]

Bug Report

Version

• tracing v0.1.20

Crates

• tracing

Description

Upgrading from tracing 0.1.19 to 0.1.20 causes tonic to no longer build with the following error:

Reproduction steps:

$ cargo new example && cd example
$ cargo add tonic
$ cargo add tracing
$ cargo build

Build output:

~/.cargo/registry/src/github.com-1ecc6299db9ec823/tower-balance-0.3.0/src/pool/mod.rs:407:21
    |
399 |         let discover = self.balance.discover_mut().as_mut().project();
    |                        ------------ mutable borrow occurs here
...
407 |                     tracing::trace!({ ewma = %self.ewma }, "pool is under-provisioned");
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |                     |                         |
    |                     |                         second borrow occurs due to use of `self` in closure
    |                     immutable borrow occurs here
408 |                 }
409 |                 *discover.load = Level::High;
    |                 ---------------------------- mutable borrow later used here
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

[hawkw]

Thanks. I think this is not specific to tonic but potentially an issue with the way closures are now used to capture values in #943. This might be an interaction with the code generated by pin-project, or just something we missed with the tests for various kinds of macro invocations.

I went ahead and yanked 0.1.20 so we don't break any more builds until this is fixed.