RUSTC_LOG shows output prefixed with `2:rustc`

[jyn514]

For example:

$ RUSTC_LOG=rustc_interface=info rustc +stage1 tcp.rs --crate-type lib
2:rustc INFO rustc_interface::passes 0 parse sess buffered_lints
2:rustc INFO rustc_interface::passes Pre-codegen
2:rustcTy interner             total           ty lt ct all
2:rustc    Adt               :   1078 81.3%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Array             :      1  0.1%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Slice             :      1  0.1%,  0.0%   0.0%  0.0%  0.0%
2:rustc    RawPtr            :      2  0.2%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Ref               :      4  0.3%,  0.1%   0.1%  0.0%  0.0%
2:rustc    FnDef             :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    FnPtr             :     76  5.7%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Placeholder       :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Generator         :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    GeneratorWitness  :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Dynamic           :      3  0.2%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Closure           :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Tuple             :     13  1.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Bound             :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Param             :    146 11.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Infer             :      2  0.2%,  0.1%   0.0%  0.0%  0.0%
2:rustc    Projection        :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Opaque            :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc    Foreign           :      0  0.0%,  0.0%   0.0%  0.0%  0.0%
2:rustc                  total   1326         0.2%   0.1%  0.0%  0.0%
2:rustcInternalSubsts interner: #437
2:rustcRegion interner: #355
2:rustcStability interner: #1
2:rustcConst Stability interner: #0
2:rustcAllocation interner: #0
2:rustcLayout interner: #0

There are two issues here:

1. Is 2:rustc actually helpful? All the code runs in the same thread with the same name, so it doesn't add any more info
2. There's no space between the output and the header, so it's hard to read the logs.

cc @hawkw, @oli-obk

[hawkw]

I believe the tracing-tree crate, which rustc is using, provides methods for disabling thread IDs and thread names when constructing its layer, so it should be possible to turn this off.

I believe the missing space is probably a bug in that crate, so I'd report it upstream. It's possible this was the intended formatting, you'd probably need to ask @davidbarsky to be sure.

[jyn514]

I believe the tracing-tree crate, which rustc is using, provides methods for disabling thread IDs and thread names when constructing its layer, so it should be possible to turn this off.

Thanks, I'll do that :)