fix(log): enable ansi color only in terminal

[weihanglo]

What does this PR try to resolve?

In #12458 we introduced tracing but forgot to consult if it is in tty to enable color logs.

How should we test and review this PR?

cargo tree &> log and check if log file contains any ansi color code.

Additional information

I'll hold off CARGO_LOG respecting --color=always for now.

#9012 is something can be resolved as a whole. tracing_subscriber::reload is also a thing to consider, so that we can configure logging color and output file after loading config.toml

[rustbot]

r? @epage

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[weihanglo]

IIUC, this is aligned with how env_logger handles ASNI color codes: https://github.com/rust-cli/env_logger/blob/bdc25caee0c27fbb1c9c66d6492a5910aaf3ac1d/src/fmt/writer/atty.rs

[weihanglo]

Currently blocked on rust-lang/rust#114804.

While we can switch from main.rs to an empty lib.rs to bypass that, I do think this is a good test to catch this kind of subtle change.

diff --git a/tests/testsuite/future_incompat_report.rs b/tests/testsuite/future_incompat_report.rs
index 9f451a64c..4d2c66d17 100644
--- a/tests/testsuite/future_incompat_report.rs
+++ b/tests/testsuite/future_incompat_report.rs
@@ -164,7 +164,7 @@ fn test_multi_crate() {
                 second-dep = "*"
               "#,
         )
-        .file("src/main.rs", "fn main() {}")
+        .file("src/lib.rs", "")
         .build();
 
     for command in &["build", "check", "rustc", "test"] {

[epage]

r= me when this is able to go through

[weihanglo]

Thank you for the review!

@bors r+

[bors]

📌 Commit c07043b has been approved by weihanglo

It is now in the queue for this repository.

[weihanglo]

@bors r-

[bors]

⌛ Testing commit c07043b with merge c3136a8...

[weihanglo]

@bors r=epage

[bors]

📌 Commit c07043b has been approved by epage

It is now in the queue for this repository.

[bors]

⌛ Testing commit c07043b with merge f137594...

[bors]

☀️ Test successful - checks-actions
Approved by: epage
Pushing f137594 to master...