[WIP Do not merge] Helpful stack overflow messages.

src/libstd/sys_common/util.rs

@@ -13,6 +13,9 @@ use io::prelude::*;
 use sys::stdio::{Stderr, stderr_prints_nothing};
 use thread;
 
+#[cfg(feature = "backtrace")]
+use sys_common::backtrace;
+
 pub fn dumb_print(args: fmt::Arguments) {
     if stderr_prints_nothing() {
         return
@@ -34,4 +37,21 @@ pub fn abort(args: fmt::Arguments) -> ! {
 pub unsafe fn report_overflow() {
     dumb_print(format_args!("\nthread '{}' has overflowed its stack\n",
                             thread::current().name().unwrap_or("<unknown>")));
+
+    #[cfg(feature = "backtrace")]
+    {
+        let log_backtrace = backtrace::log_enabled();
+
+        use sync::atomic::{AtomicBool, Ordering};
+
+        static FIRST_OVERFLOW: AtomicBool = AtomicBool::new(true);
+
+        if let Some(format) = log_backtrace {
+            if let Ok(mut stderr) = Stderr::new() {
+                let _ = backtrace::print(&mut stderr, format);
+            }
+        } else if FIRST_OVERFLOW.compare_and_swap(true, false, Ordering::SeqCst) {
+            dumb_print(format_args!("note: Run with `RUST_BACKTRACE=1` for a backtrace."));
+        }
+    }
 }

src/test/run-pass/stack-probes.rs

@@ -73,4 +73,5 @@ fn assert_overflow(cmd: &mut Command) {
     println!("stderr: {}", stderr);
     assert!(stdout.is_empty());
     assert!(stderr.contains("has overflowed its stack\n"));
+    assert!(stderr.contains("::"));
 }