Rollup merge of rust-lang#116586 - SparrowLii:parallel_log, r=oli-obk

use env variable to control thread ids in rustc_log

Currently, when parallel rustc is enabled, even if the number of threads is 1, the thread ID will be included before all the logs.
E.g.
`WARN rustc_mir_build::thir::pattern::const_to_pat ...`
=>
`2:rustcWARN rustc_mir_build::thir::pattern::const_to_pat ...`
This makes the logs confusing and results in inconsistent UI test results for serial and parallel rustc. Therefore I think we should let users decide whether thread id information is needed through explicit control.

Author: matthiaskrgr

compiler/rustc_log/src/lib.rs

@@ -74,16 +74,21 @@ pub fn init_env_logger(env: &str) -> Result<(), Error> {
         Some(v) => &v != "0",
     };
 
+    let verbose_thread_ids = match env::var_os(String::from(env) + "_THREAD_IDS") {
+        None => false,
+        Some(v) => &v == "1",
+    };
+
     let layer = tracing_tree::HierarchicalLayer::default()
         .with_writer(io::stderr)
         .with_indent_lines(true)
         .with_ansi(color_logs)
         .with_targets(true)
         .with_verbose_exit(verbose_entry_exit)
         .with_verbose_entry(verbose_entry_exit)
-        .with_indent_amount(2);
-    #[cfg(all(parallel_compiler, debug_assertions))]
-    let layer = layer.with_thread_ids(true).with_thread_names(true);
+        .with_indent_amount(2)
+        .with_thread_ids(verbose_thread_ids)
+        .with_thread_names(verbose_thread_ids);
 
     let subscriber = tracing_subscriber::Registry::default().with(filter).with(layer);
     match env::var(format!("{env}_BACKTRACE")) {