Print thread ID in panic message if thread name is unknown

`panic!` does not print any identifying information for threads that are
unnamed. However, in many cases, the thread ID can be determined.

This changes the panic message from something like this:

    thread '<unnamed>' panicked at src/main.rs:3:5:
    explicit panic

To something like this:

    thread '<unnamed>' (1234) panicked at src/main.rs:3:5:
    explicit panic

This change applies to both named and unnamed threads. There is no
change for threads where an ID cannot be determined.

library/std/src/panicking.rs

@@ -250,10 +250,15 @@ fn default_hook(info: &PanicHookInfo<'_>) {
 
     let msg = payload_as_str(info.payload());
     let thread = thread::try_current();
-    let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
+    let thread_info = thread.as_ref().map(|t| (t.id().as_u64(), t.name().unwrap_or("<unnamed>")));
 
     let write = |err: &mut dyn crate::io::Write| {
-        let _ = writeln!(err, "thread '{name}' panicked at {location}:\n{msg}");
+        let _ = match thread_info {
+            Some((id, name)) => {
+                writeln!(err, "thread '{name}' ({id}) panicked at {location}:\n{msg}")
+            }
+            None => writeln!(err, "thread '<unnamed>' panicked at {location}:\n{msg}"),
+        };
 
         static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
 

tests/ui/proc-macro/load-panic-backtrace.rs

@@ -1,7 +1,7 @@
 //@ aux-build:test-macros.rs
 //@ compile-flags: -Z proc-macro-backtrace
 //@ rustc-env:RUST_BACKTRACE=0
-//@ normalize-stderr-test "thread '.*' panicked " -> ""
+//@ normalize-stderr-test "thread '.*' \(\d+\) panicked " -> ""
 //@ normalize-stderr-test "note:.*RUST_BACKTRACE=1.*\n" -> ""
 //@ needs-unwind proc macro panics to report errors
 

tests/ui/process/multi-panic.rs

@@ -8,11 +8,11 @@ fn check_for_no_backtrace(test: std::process::Output) {
     let err = String::from_utf8_lossy(&test.stderr);
     let mut it = err.lines();
 
-    assert_eq!(it.next().map(|l| l.starts_with("thread '<unnamed>' panicked")), Some(true));
+    assert_eq!(it.next().map(|l| l.starts_with("thread '<unnamed>' (")), Some(true));
     assert_eq!(it.next().is_some(), true);
     assert_eq!(it.next(), Some("note: run with `RUST_BACKTRACE=1` \
                                 environment variable to display a backtrace"));
-    assert_eq!(it.next().map(|l| l.starts_with("thread 'main' panicked at")), Some(true));
+    assert_eq!(it.next().map(|l| l.starts_with("thread 'main' (")), Some(true));
     assert_eq!(it.next().is_some(), true);
     assert_eq!(it.next(), None);
 }

tests/ui/test-attrs/terse.rs

@@ -4,6 +4,7 @@
 //@ check-run-results
 //@ exec-env:RUST_BACKTRACE=0
 //@ normalize-stdout-test "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ normalize-stdout-test "(thread '.*') \(\d+\)" -> "$1 (tid)"
 //@ ignore-emscripten no threads support
 //@ needs-unwind
 

tests/ui/test-attrs/terse.run.stdout

@@ -9,16 +9,16 @@ foo2 --- FAILED
 failures:
 
 ---- abc stdout ----
-thread 'abc' panicked at $DIR/terse.rs:12:5:
+thread 'abc' (tid) panicked at $DIR/terse.rs:13:5:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 
 ---- foo stdout ----
-thread 'foo' panicked at $DIR/terse.rs:17:5:
+thread 'foo' (tid) panicked at $DIR/terse.rs:18:5:
 explicit panic
 
 ---- foo2 stdout ----
-thread 'foo2' panicked at $DIR/terse.rs:22:5:
+thread 'foo2' (tid) panicked at $DIR/terse.rs:23:5:
 explicit panic
 
 

tests/ui/test-attrs/test-panic-abort.rs

@@ -5,6 +5,7 @@
 //@ check-run-results
 //@ exec-env:RUST_BACKTRACE=0
 //@ normalize-stdout-test "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ normalize-stdout-test "(thread '.*') \(\d+\)" -> "$1 (tid)"
 
 //@ ignore-android #120567
 //@ ignore-wasm no panic or subprocess support

tests/ui/test-attrs/test-panic-abort.run.stdout

@@ -17,7 +17,7 @@ hello, world
 testing123
 ---- it_fails stderr ----
 testing321
-thread 'main' panicked at $DIR/test-panic-abort.rs:39:5:
+thread 'main' (tid) panicked at $DIR/test-panic-abort.rs:40:5:
 assertion `left == right` failed
   left: 2
  right: 5