Fix slow memory leak in console.trace()

src/bun.js/ConsoleObject.zig

@@ -633,8 +633,8 @@ pub fn writeTrace(comptime Writer: type, writer: Writer, global: *JSGlobalObject
     var source_code_slice: ?ZigString.Slice = null;
     defer if (source_code_slice) |slice| slice.deinit();
 
-    var err = ZigString.init("trace output").toErrorInstance(global);
-    err.toZigException(global, exception);
+    const err = ZigString.init("trace output").toErrorInstance(global);
+    // remapZigException will call .toZigException() on the ErrorInstance.
     vm.remapZigException(
         exception,
         err,

src/logger.zig

@@ -383,6 +383,7 @@ pub const Msg = struct {
 
     pub fn fromJS(allocator: std.mem.Allocator, globalObject: *bun.JSC.JSGlobalObject, file: string, err: bun.JSC.JSValue) !Msg {
         var zig_exception_holder: bun.JSC.ZigException.Holder = bun.JSC.ZigException.Holder.init();
+        defer zig_exception_holder.deinit(globalObject.bunVM());
         if (err.toError()) |value| {
             value.toZigException(globalObject, zig_exception_holder.zigException());
         } else {

test/js/web/console/console-trace-leak-fixture.js

@@ -0,0 +1,19 @@
+for (let i = 0; i < 1024; i++) {
+  eval(`console.trace();`);
+}
+Bun.gc(true);
+const baseline = process.memoryUsage.rss();
+
+for (let j = 0; j < 1024; j++) {
+  for (let i = 0; i < 1024; i++) {
+    eval(`console.trace();`);
+  }
+}
+Bun.gc(true);
+const delta = ((process.memoryUsage.rss() - baseline) / 1024 / 1024) | 0;
+console.error(delta, "MB", "delta");
+// on macOS in a debug build, this was 124 MB after fixing the leak.
+// on macOS in a leaking release build, this was 239 MB.
+if (delta > 200) {
+  throw new Error("Memory leak detected");
+}

test/js/web/console/console-trace-leak.test.ts

@@ -0,0 +1,9 @@
+import { test, expect, describe, it } from "bun:test";
+import "harness";
+import path from "node:path";
+describe("console.trace leak", () => {
+  test("should not leak", async () => {
+    expect(["--smol", path.join(import.meta.dir, "console-trace-leak-fixture.js")]).toRun();
+    // This is a lot slower in a debug build.
+  }, 60_000);
+});