tracing-subscriber: filtering not working for spans with dashes in their names

[rwestphal]

Description

Filtering log events using the target[span{field=value}]=level syntax doesn't work when the span name contains a dash.

Example log events from my program:

Apr 22 17:24:50.315 DEBUG ldp-instance{name="main"}:targeted-nbr{address=4.4.4.4}:discovery: received hello message source=4.4.4.4 lsr_id=4.4.4.4
Apr 22 17:24:50.316 DEBUG ldp-instance{name="main"}:interface{name=eth-rt2}:discovery: received hello message source=10.0.1.2 lsr_id=2.2.2.2
Apr 22 17:24:50.316 DEBUG ldp-instance{name="main"}:targeted-nbr{address=4.4.4.4}:discovery: sending hello message
Apr 22 17:24:50.316 DEBUG ldp-instance{name="main"}:targeted-nbr{address=4.4.4.4}:discovery: received hello message source=4.4.4.4 lsr_id=4.4.4.4
Apr 22 17:24:50.758 DEBUG ldp-instance{name="main"}:interface{name=eth-rt2}:discovery: sending hello message

While I can use RUST_LOG=holo[interface]=debug cargo run to filter interface events only, I can't do the same for targeted-nbr or ldp-instance. Renaming those spans to targeted_nbr and ldp_instance, respectively, allows the filtering to work normally.

I didn't check if the same problem happens for span field names.

Version

# cargo tree | grep tracing
│   │   ├── tracing v0.1.25
│   │   │   ├── tracing-attributes v0.1.15 (proc-macro)
│   │   │   └── tracing-core v0.1.17
│   ├── tracing v0.1.25 (*)
│   │   └── tracing v0.1.25 (*)
│   │   ├── tracing v0.1.25 (*)
│   │   └── tracing v0.1.25 (*)
│   ├── tracing v0.1.25 (*)
│   └── tracing-futures v0.2.5
│       └── tracing v0.1.25 (*)
├── tracing v0.1.25 (*)
├── tracing-subscriber v0.2.17
│   ├── tracing v0.1.25 (*)
│   ├── tracing-core v0.1.17 (*)
│   ├── tracing-log v0.1.2
│   │   └── tracing-core v0.1.17 (*)
│   └── tracing-serde v0.1.2
│       └── tracing-core v0.1.17 (*)

Platform

Linux debian 4.19.0-16-amd64 #1 SMP Debian 4.19.181-1 (2021-03-19) x86_64 GNU/Linux