tracing-subscriber: inconsistent behavior between `init` methods

[cgbur]

Bug Report

Version

tracing-subscriber v0.3.14 tracing v0.1.35

Platform

x86_64-unknown-linux-gnu

Crates

tracing-subscriber

Description

There appears to be a discrepancy in what the documentation believes is true and what the different format initializers actually do. tracing_subscriber::fmt::init() has documentation saying it is the same as tracing_subscriber::fmt().init(). I think there may be two bugs.

1. That code eventually calls builder.with_max_level(LevelFilter::TRACE) instead of using DEFAULT_MAX_LEVEL which is set to INFO.
2. tracing_subscriber::fmt().init() does NOT use env filters and tracing_subscriber::fmt::init() does. This leads to confusing behavior when switching between implementations that are supposed to be the same. NOTE, as far as I can tell this is fixed in main branch.

Example

To reproduce bug 2:

# cargo.toml

[package]
name = "tracing-test"
version = "0.1.0"
edition = "2021"

[dependencies]
tracing-subscriber = "0.3"
tracing = "0.1"

using fmt::init()

fn main() {
    tracing_subscriber::fmt::init();

    tracing::error!("error");
    tracing::warn!("warn");
    tracing::info!("info");
    tracing::debug!("debug");
    tracing::trace!("trace");
}

❯ RUST_LOG=TRACE cargo run --
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/tracing-test`
2022-07-12T17:37:31.613776Z ERROR tracing_test: error
2022-07-12T17:37:31.613807Z  WARN tracing_test: warn
2022-07-12T17:37:31.613820Z  INFO tracing_test: info
2022-07-12T17:37:31.613832Z DEBUG tracing_test: debug
2022-07-12T17:37:31.613843Z TRACE tracing_test: trace

using fmt().init()

fn main() {
    tracing_subscriber::fmt().init();

    tracing::error!("error");
    tracing::warn!("warn");
    tracing::info!("info");
    tracing::debug!("debug");
    tracing::trace!("trace");
}

❯ RUST_LOG=TRACE cargo run --
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/tracing-test`
2022-07-12T17:38:33.822023Z ERROR tracing_test: error
2022-07-12T17:38:33.822055Z  WARN tracing_test: warn
2022-07-12T17:38:33.822067Z  INFO tracing_test: info

[davidbarsky]

This issue is a duplicate of #1329, but you're right about the discrepancy. Would you be willing to submit a PR to the v0.1.0 branch fixing the incorrect documentation on tracing_subscriber::fmt().init()?

[cgbur]

Is the correct thing to do here to change the comment to reflect that they are not the same or to fix the code so that they are the same?

I can see the argument for changing just the documentation since somebody might already rely on this functionality and 0.2 does not have this problem.

[davidbarsky]

At the moment, we should just change the documentation to reflect reality. The right solution might require a bit more thought.