Add log-backtrace option to show backtraces along with logging

Cargo.lock

@@ -4273,6 +4273,7 @@ version = "0.0.0"
 dependencies = [
  "rustc_span",
  "tracing",
+ "tracing-core",
  "tracing-subscriber",
  "tracing-tree",
 ]

compiler/rustc_driver/src/lib.rs

@@ -231,6 +231,10 @@ 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, input_file_path))) => {
@@ -1299,7 +1303,14 @@ 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() {
-    if let Err(error) = rustc_log::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());
     }
 }
@@ -1365,7 +1376,6 @@ 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

@@ -748,6 +748,7 @@ 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/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 tracing = "0.1.28"
 tracing-subscriber = { version = "0.3.3", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"] }
 tracing-tree = "0.2.0"
+tracing-core = "0.1.28"
 
 [dev-dependencies]
 rustc_span = { path = "../rustc_span" }

compiler/rustc_log/src/lib.rs

@@ -45,16 +45,34 @@
 use std::env::{self, VarError};
 use std::fmt::{self, Display};
 use std::io::{self, IsTerminal};
+use tracing_core::{Event, Subscriber};
 use tracing_subscriber::filter::{Directive, EnvFilter, LevelFilter};
+use tracing_subscriber::fmt::{
+    format::{self, FormatEvent, FormatFields},
+    FmtContext,
+};
 use tracing_subscriber::layer::SubscriberExt;
 
 pub fn init_rustc_env_logger() -> Result<(), Error> {
-    init_env_logger("RUSTC_LOG")
+    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)
 }
 
 /// 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)),
@@ -88,11 +106,47 @@ pub fn init_env_logger(env: &str) -> Result<(), Error> {
     let layer = layer.with_thread_ids(true).with_thread_names(true);
 
     let subscriber = tracing_subscriber::Registry::default().with(filter).with(layer);
-    tracing::subscriber::set_global_default(subscriber).unwrap();
+    match backtrace_target {
+        Some(str) => {
+            let fmt_layer = tracing_subscriber::fmt::layer()
+                .with_writer(io::stderr)
+                .without_time()
+                .event_format(BacktraceFormatter { backtrace_target: str.to_string() });
+            let subscriber = subscriber.with(fmt_layer);
+            tracing::subscriber::set_global_default(subscriber).unwrap();
+        }
+        None => {
+            tracing::subscriber::set_global_default(subscriber).unwrap();
+        }
+    };
 
     Ok(())
 }
 
+struct BacktraceFormatter {
+    backtrace_target: String,
+}
+
+impl<S, N> FormatEvent<S, N> for BacktraceFormatter
+where
+    S: Subscriber + for<'a> tracing_subscriber::registry::LookupSpan<'a>,
+    N: for<'a> FormatFields<'a> + 'static,
+{
+    fn format_event(
+        &self,
+        _ctx: &FmtContext<'_, S, N>,
+        mut writer: format::Writer<'_>,
+        event: &Event<'_>,
+    ) -> fmt::Result {
+        let target = event.metadata().target();
+        if !target.contains(&self.backtrace_target) {
+            return Ok(());
+        }
+        let backtrace = std::backtrace::Backtrace::capture();
+        writeln!(writer, "stack backtrace: \n{:?}", backtrace)
+    }
+}
+
 pub fn stdout_isatty() -> bool {
     io::stdout().is_terminal()
 }

compiler/rustc_session/src/options.rs

@@ -1411,6 +1411,8 @@ 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

@@ -76,6 +76,7 @@
     -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

@@ -0,0 +1,9 @@
+// run-pass
+//
+// This test makes sure that log-backtrace option doesn't give a compilation error.
+//
+// dont-check-compiler-stdout
+// dont-check-compiler-stderr
+// rustc-env:RUSTC_LOG=info
+// compile-flags: -Zlog-backtrace=rustc_metadata::creader
+fn main() {}