Guard AggregateError .errors printing against self-reference

src/jsc/VirtualMachine.rs

@@ -4469,6 +4469,7 @@ impl VirtualMachine {
         allow_side_effects: bool,
     ) {
         let mut formatter = crate::console_object::Formatter::new(self.global());
+        formatter.stack_check = bun_core::StackCheck::init();
         let colors = bun_core::Output::enable_ansi_colors_stderr();
         self.print_errorlike_object(
             exception.value(),
@@ -4785,6 +4786,41 @@ impl VirtualMachine {
         let global_ref = self.global();
 
         if value.is_aggregate_error(global_ref) {
+            // Same stack + cycle guard the `cause` chain gets in `print_error_instance_body`.
+            if !formatter.stack_check.is_safe_to_recurse() {
+                formatter.failed = true;
+                if formatter.can_throw_stack_overflow {
+                    let _ = global_ref.throw_stack_overflow();
+                }
+                return;
+            }
+            if formatter.map_node.is_none() {
+                let mut node =
+                    NonNull::new(crate::console_object::formatter::visited::Pool::get_node())
+                        .expect("ObjectPool::get_node always returns a valid heap node");
+                let data = crate::console_object::formatter::visited::node_data_mut(&mut node);
+                data.clear();
+                formatter.map = core::mem::take(data);
+                formatter.map_node = Some(node);
+            }
+            if formatter
+                .map
+                .get_or_put(value)
+                .expect("unreachable")
+                .found_existing
+            {
+                let _ = if allow_ansi_color {
+                    writer.write_all(
+                        bun_core::pretty_fmt!("<r><cyan>[Circular]<r>\n", true).as_bytes(),
+                    )
+                } else {
+                    writer.write_all(
+                        bun_core::pretty_fmt!("<r><cyan>[Circular]<r>\n", false).as_bytes(),
+                    )
+                };
+                return;
+            }
+
             // Note: `JSValue::for_each` takes a C-ABI fn
             // pointer + erased ctx, so thread the captures through a struct.
             // The C trampoline erases lifetimes via `*mut c_void`; round-trip
@@ -4817,6 +4853,9 @@ impl VirtualMachine {
                 // SAFETY: `ctx.formatter` borrows the caller's stack local,
                 // live across the synchronous `for_each` call.
                 let formatter = unsafe { &mut *ctx.formatter };
+                if formatter.failed {
+                    return;
+                }
                 // SAFETY: `ctx.writer` borrows the caller's stack local,
                 // live across the synchronous `for_each` call.
                 let writer = unsafe { &mut *ctx.writer };
@@ -4844,6 +4883,7 @@ impl VirtualMachine {
             // which case the error is swallowed.
             let errors = value.get_errors_property(global_ref);
             let _ = errors.for_each(global_ref, (&raw mut ctx).cast(), agg_iter);
+            let _ = formatter.map.remove(&value);
             return;
         }
 

src/runtime/jsc_hooks.rs

@@ -1194,6 +1194,7 @@ fn print_exception(
         vm_ref.print_exception(exception, exception_list, writer, true);
     } else {
         let mut formatter = bun_jsc::console_object::Formatter::new(global);
+        formatter.stack_check = bun_core::StackCheck::init();
         // `Formatter::new` already
         // defaults `error_display_level` to `Full` (ConsoleObject.rs:1176).
         let colors = bun_core::Output::enable_ansi_colors_stderr();

test/js/node/util/bun-inspect.test.ts

@@ -1,4 +1,5 @@
 import { describe, expect, it } from "bun:test";
+import { bunEnv, bunExe } from "harness";
 import stripAnsi from "strip-ansi";
 
 describe("Bun.inspect", () => {
@@ -87,6 +88,60 @@ describe("Bun.inspect", () => {
     );
   });
 
+  it("self-referential AggregateError prints [Circular]", () => {
+    const ae: any = new AggregateError([], "circ");
+    ae.errors.push(ae);
+    const out = Bun.inspect(ae);
+    expect(out).toContain("[Circular]");
+  });
+
+  it("deeply nested AggregateError throws a stack overflow instead of crashing", () => {
+    let e: unknown = new Error("leaf");
+    for (let i = 0; i < 16 * 1024; i++) {
+      e = new AggregateError([e], "agg");
+    }
+    expect(() => Bun.inspect(e)).toThrowErrorMatchingInlineSnapshot(`"Maximum call stack size exceeded."`);
+  });
+
+  it.concurrent.each([
+    ["console.log", `console.log(ae);`, 0],
+    ["Bun.inspect", `process.stdout.write(Bun.inspect(ae));`, 0],
+    ["throw", `throw ae;`, 1],
+    ["Promise.reject", `Promise.reject(ae); await 0;`, 1],
+  ])("self-referential AggregateError via %s does not crash", async (name, emit, expectedExit) => {
+    const src = `const ae = new AggregateError([], "circ"); ae.errors.push(ae); ${emit}`;
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "-e", src],
+      env: bunEnv,
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    const output = stdout + stderr;
+    expect(output).toContain("[Circular]");
+    expect(proc.signalCode).toBeNull();
+    expect(exitCode).toBe(expectedExit);
+  });
+
+  it.concurrent.each([
+    ["throw", `throw e;`],
+    ["Promise.reject", `Promise.reject(e); await 0;`],
+  ])("deeply nested AggregateError via %s does not crash", async (name, emit) => {
+    // Fan-out of 2 so the test also covers the `formatter.failed` short-circuit
+    // in `agg_iter`; without it the throw path re-descends per sibling and hangs.
+    const src = `let e = new Error("leaf"); for (let i = 0; i < 16 * 1024; i++) e = new AggregateError([e, e], "agg"); process.stderr.write("built\\n"); ${emit}`;
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "-e", src],
+      env: bunEnv,
+      stdout: "ignore",
+      stderr: "pipe",
+    });
+    const [stderr, exitCode] = await Promise.all([proc.stderr.text(), proc.exited]);
+    expect(stderr.slice(0, 6)).toBe("built\n");
+    expect(proc.signalCode).toBeNull();
+    expect(exitCode).toBe(1);
+  });
+
   it("depth = 0", () => {
     expect(Bun.inspect({ a: { b: { c: { d: 1 } } } }, { depth: 0 })).toEqual("{\n  a: [Object ...],\n}");
   });