Replace a command line flag with an env var to allow tools to initialize the tracing loggers at their own discretion

compiler/rustc_driver_impl/src/lib.rs

@@ -229,10 +229,6 @@ fn run_compiler(
         registry: diagnostics_registry(),
     };
 
-    if !tracing::dispatcher::has_been_set() {
-        init_rustc_env_logger_with_backtrace_option(&config.opts.unstable_opts.log_backtrace);
-    }
-
     match make_input(config.opts.error_format, &matches.free) {
         Err(reported) => return Err(reported),
         Ok(Some(input)) => {
@@ -1253,16 +1249,7 @@ pub fn install_ice_hook() {
 /// This allows tools to enable rust logging without having to magically match rustc's
 /// tracing crate version.
 pub fn init_rustc_env_logger() {
-    init_rustc_env_logger_with_backtrace_option(&None);
-}
-
-/// This allows tools to enable rust logging without having to magically match rustc's
-/// tracing crate version. In contrast to `init_rustc_env_logger` it allows you to
-/// choose a target module you wish to show backtraces along with its logging.
-pub fn init_rustc_env_logger_with_backtrace_option(backtrace_target: &Option<String>) {
-    if let Err(error) = rustc_log::init_rustc_env_logger_with_backtrace_option(backtrace_target) {
-        early_error(ErrorOutputType::default(), &error.to_string());
-    }
+    init_env_logger("RUSTC_LOG");
 }
 
 /// This allows tools to enable rust logging without having to magically match rustc's
@@ -1326,6 +1313,7 @@ mod signal_handler {
 pub fn main() -> ! {
     let start_time = Instant::now();
     let start_rss = get_resident_set_size();
+    init_rustc_env_logger();
     signal_handler::install();
     let mut callbacks = TimePassesCallbacks::default();
     install_ice_hook();

compiler/rustc_interface/src/tests.rs

@@ -758,7 +758,6 @@ fn test_unstable_options_tracking_hash() {
     tracked!(link_only, true);
     tracked!(llvm_plugins, vec![String::from("plugin_name")]);
     tracked!(location_detail, LocationDetail { file: true, line: false, column: false });
-    tracked!(log_backtrace, Some("filter".to_string()));
     tracked!(maximal_hir_to_mir_coverage, true);
     tracked!(merge_functions, Some(MergeFunctions::Disabled));
     tracked!(mir_emit_retag, true);

compiler/rustc_log/src/lib.rs

@@ -54,25 +54,12 @@ use tracing_subscriber::fmt::{
 use tracing_subscriber::layer::SubscriberExt;
 
 pub fn init_rustc_env_logger() -> Result<(), Error> {
-    init_rustc_env_logger_with_backtrace_option(&None)
-}
-
-pub fn init_rustc_env_logger_with_backtrace_option(
-    backtrace_target: &Option<String>,
-) -> Result<(), Error> {
-    init_env_logger_with_backtrace_option("RUSTC_LOG", backtrace_target)
+    init_env_logger("RUSTC_LOG")
 }
 
 /// In contrast to `init_rustc_env_logger` this allows you to choose an env var
 /// other than `RUSTC_LOG`.
 pub fn init_env_logger(env: &str) -> Result<(), Error> {
-    init_env_logger_with_backtrace_option(env, &None)
-}
-
-pub fn init_env_logger_with_backtrace_option(
-    env: &str,
-    backtrace_target: &Option<String>,
-) -> Result<(), Error> {
     let filter = match env::var(env) {
         Ok(env) => EnvFilter::new(env),
         _ => EnvFilter::default().add_directive(Directive::from(LevelFilter::WARN)),
@@ -106,8 +93,8 @@ pub fn init_env_logger_with_backtrace_option(
     let layer = layer.with_thread_ids(true).with_thread_names(true);
 
     let subscriber = tracing_subscriber::Registry::default().with(filter).with(layer);
-    match backtrace_target {
-        Some(str) => {
+    match env::var(format!("{env}_BACKTRACE")) {
+        Ok(str) => {
             let fmt_layer = tracing_subscriber::fmt::layer()
                 .with_writer(io::stderr)
                 .without_time()
@@ -115,7 +102,7 @@ pub fn init_env_logger_with_backtrace_option(
             let subscriber = subscriber.with(fmt_layer);
             tracing::subscriber::set_global_default(subscriber).unwrap();
         }
-        None => {
+        Err(_) => {
             tracing::subscriber::set_global_default(subscriber).unwrap();
         }
     };

compiler/rustc_session/src/options.rs

@@ -1413,8 +1413,6 @@ options! {
         "what location details should be tracked when using caller_location, either \
         `none`, or a comma separated list of location details, for which \
         valid options are `file`, `line`, and `column` (default: `file,line,column`)"),
-    log_backtrace: Option<String> = (None, parse_opt_string, [TRACKED],
-        "add a backtrace along with logging"),
     ls: bool = (false, parse_bool, [UNTRACKED],
         "list the symbols defined by a library crate (default: no)"),
     macro_backtrace: bool = (false, parse_bool, [UNTRACKED],

tests/rustdoc-ui/z-help.stdout

@@ -77,7 +77,6 @@
     -Z                            llvm-plugins=val -- a list LLVM plugins to enable (space separated)
     -Z                         llvm-time-trace=val -- generate JSON tracing data file from LLVM data (default: no)
     -Z                         location-detail=val -- what location details should be tracked when using caller_location, either `none`, or a comma separated list of location details, for which valid options are `file`, `line`, and `column` (default: `file,line,column`)
-    -Z                           log-backtrace=val -- add a backtrace along with logging
     -Z                                      ls=val -- list the symbols defined by a library crate (default: no)
     -Z                         macro-backtrace=val -- show macro backtraces (default: no)
     -Z             maximal-hir-to-mir-coverage=val -- save as much information as possible about the correspondence between MIR and HIR as source scopes (default: no)

tests/ui/attributes/log-backtrace.rs

@@ -1,9 +1,9 @@
 // run-pass
 //
-// This test makes sure that log-backtrace option doesn't give a compilation error.
+// This test makes sure that log-backtrace option at least parses correctly
 //
 // dont-check-compiler-stdout
 // dont-check-compiler-stderr
 // rustc-env:RUSTC_LOG=info
-// compile-flags: -Zlog-backtrace=rustc_metadata::creader
+// rustc-env:RUSTC_LOG_BACKTRACE=rustc_metadata::creader
 fn main() {}