Start work on detecting leaked handles in tests

For now, just track models. Tests fail because we don't
yet clear the app contexts at the right time.

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/gpui/src/util.rs

@@ -1,5 +1,6 @@
+use backtrace::{Backtrace, BacktraceFmt, BytesOrWideString};
 use smol::future::FutureExt;
-use std::{future::Future, time::Duration};
+use std::{fmt, future::Future, time::Duration};
 
 pub fn post_inc(value: &mut usize) -> usize {
     let prev = *value;
@@ -18,3 +19,27 @@ where
     let future = async move { Ok(f.await) };
     timer.race(future).await
 }
+
+pub struct CwdBacktrace<'a>(pub &'a Backtrace);
+
+impl<'a> std::fmt::Debug for CwdBacktrace<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> std::fmt::Result {
+        let cwd = std::env::current_dir().unwrap();
+        let cwd = cwd.parent().unwrap();
+        let mut print_path = |fmt: &mut fmt::Formatter<'_>, path: BytesOrWideString<'_>| {
+            fmt::Display::fmt(&path, fmt)
+        };
+        let mut fmt = BacktraceFmt::new(f, backtrace::PrintFmt::Full, &mut print_path);
+        for frame in self.0.frames() {
+            let mut formatted_frame = fmt.frame();
+            if frame
+                .symbols()
+                .iter()
+                .any(|s| s.filename().map_or(false, |f| f.starts_with(&cwd)))
+            {
+                formatted_frame.backtrace_frame(frame)?;
+            }
+        }
+        fmt.finish()
+    }
+}