bake: exit a successful bun build --app through the build VM

[robobun]

Problem

• A bun build --app that renders successfully exits without going through its build VM's exit sequence. Three things are skipped as a result:
  • process.on("exit") handlers registered by the app config or by the prerendered modules never run.
  • process.exitCode set during prerendering is ignored; the process always exits 0.
  • Under BUN_DESTRUCT_VM_ON_EXIT=1 (what the ASAN CI lane runs tests with), the JSC VM is never destroyed, so every native object still owned by a JS wrapper created during prerendering is never freed. For a react app with one page, LeakSanitizer reports 10 allocations: 2x ImmediateObject (bun_runtime::timer::All::set_immediate, react's scheduler), 2x Blob (bun_jsc::webcore_types::Blob::new) and 2x TextDecoder (TextDecoder::new), plus their indirect buffers.
• Cause: build_command in src/runtime/bake/production.rs only called vm.on_exit() and vm.global_exit() in the Err(JSError) arm of the build_with_vm match. The Ok arm returned, the scopeguard created at the top of the function ran release_queued_work() + destroy() (the Rust side of the VM only), and main then called Global::exit(0). A build whose page throws takes the other arm and is clean under LeakSanitizer with the same environment; only the two success returns (a rendered build, and the early return when there is nothing to bundle) were affected. bake's production build is the only main-thread VM in bun that exited this way.

Fix

• build_command runs vm.on_exit() + vm.global_exit() after the match, for both the Ok and the JSError arm. The JSError arm now only prints the exception and sets the exit code to 1 if nothing set one.
• The Err(e) return (a BuildFailed from the bundler or an I/O error) is deliberately left as it was: it still returns through the scopeguard, because Cli::start is what prints the accumulated bundler log for it before exiting. It is now the scopeguard's only user.
• Why this is the right exit: on_exit + global_exit is the exit sequence every other main thread VM in bun uses (bun run, bun test, the repl), and the one the failing arm of this very function already used. global_exit exits with exit_handler.exit_code, which is where process.exitCode is stored, and under BUN_DESTRUCT_VM_ON_EXIT runs VirtualMachine::teardown, the only sequence that destroys the JSC heap and so runs the wrapper finalizers that own these natives. Nothing in the build needs the VM after build_with_vm returns: its last step is wait_for_tasks(), so the event loop is already drained when the exit handlers run.
• Without BUN_DESTRUCT_VM_ON_EXIT the VM is now left allocated at exit instead of destroy()ed, exactly as bun run leaves its VM. It stays reachable from the thread local and the stack, so LeakSanitizer does not report it: after this change the no-pages build reports the same 2870 allocations with and without the variable, all of them the transpiler allocations that bake: drop the production build's transpilers and framework projection #38233 fixes.
• Cost on a normal build: the exit event dispatch and the sqlite close that global_exit does; from the done line to process exit takes about 50ms on a debug build, and that interval includes the process exit itself.
• Verified with test/bake/dev/production.test.ts, three new cases in one describe, all run with BUN_DESTRUCT_VM_ON_EXIT=1 so the exit codes also show that a build VM's teardown completes on every platform CI runs this file on:
  • a rendered build whose config registers an exit handler and whose page sets process.exitCode = 3 prints exit event: 3 and exits 3 (before: no event, exit 0);
  • a build with no pages directory (the early return) prints exit event: 0 and exits 0 (before: no event);
  • ASAN only: the page component creates a TextDecoder, a Blob, a setImmediate handle and a Bun.CryptoHasher while it renders and parks them on globalThis; the build runs with detect_leaks=1 and the LeakSanitizer output must not name any of the four types. Before the fix it names all four (CryptoHasher is there to show the planted objects are what is measured, since the framework never creates one; the other three are the kinds the framework itself leaked). They are created during render rather than at module scope because test/leaksan.supp suppresses anything allocated while a module is being evaluated. The test checks the report's contents rather than requiring an empty report because the build's transpilers still leak at this commit (bake: drop the production build's transpilers and framework projection #38233).
  • Verified in both directions on a debug ASAN build: with src/runtime/bake/production.rs at main's version all three fail as described; with it at this branch all three pass, and so does the rest of the file, including the throwing-component case that exercises the restructured JSError arm.
  • With bake: drop the production build's transpilers and framework projection #38233 merged in locally, the rendered build, the no-pages build and the throwing build are all completely clean under LeakSanitizer with BUN_DESTRUCT_VM_ON_EXIT=1. The only report left in this test file's scenarios is the ServerComponentParseTask allocation from builds with "use client" components, which bundler: free the ServerComponentParseTask after it generates its file #38004 fixes. test/no-validate-leaksan.txt now says so next to this file's entry; whichever of the three PRs lands last can remove the entry.
  • cargo clippy -p bun_runtime and cargo fmt --check are clean.
• Overlaps textually with bake: drop the production build's transpilers and framework projection #38233 only in production.test.ts (both append tests to the same file); the production.rs changes merge cleanly.

Background

• bun build --app (bake's static production build, src/runtime/bake/production.rs) creates a dedicated VirtualMachine (init_bake) to evaluate the app config and to prerender the routes in; build_command owns that VM and build_with_vm does the work.
• VirtualMachine::on_exit emits process's exit event and runs the VM's cleanup hooks; global_exit then terminates the process with exit_handler.exit_code (the field behind process.exitCode). When BUN_DESTRUCT_VM_ON_EXIT=1 is set, global_exit first runs VirtualMachine::teardown, the ordered shutdown that cancels timers, destroys the JSC VM (running every remaining wrapper finalizer) and finally calls destroy(). Without the variable the main thread skips the teardown and lets the OS reclaim memory; CI's ASAN lane sets it so that LeakSanitizer can tell real leaks from objects that were simply alive at exit.
• VirtualMachine::destroy() frees only the Rust-owned parts of a VM (event loops, RareData, runtime state). Natives created through JS constructors (new Blob(), new TextDecoder(), setImmediate(), new Bun.CryptoHasher()) are owned by their JSC wrapper cells and are released by the cells' finalizers, so they are freed only when the JSC heap is destroyed.
• LeakSanitizer reports allocations that are unreachable at process exit. Memory still referenced from a live stack frame or a thread local is not reported; memory referenced only from JSC heap cells is, because the JSC heap is not malloc memory that LeakSanitizer scans. test/leaksan.supp additionally hides any leak whose stack contains one of the listed frames, which is why the test's objects have to be created during render and not during module evaluation.

[coderabbitai]

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Walkthrough

Changes

Production build VM exit handling

Layer / File(s)	Summary
Build result and VM exit flow src/runtime/bake/production.rs	build_command reacquires the VM after build_with_vm, reports JavaScript exceptions through it, preserves exit-code updates, and runs on_exit and global_exit for successful builds and JavaScript failures.
Exit sequencing and teardown tests test/bake/dev/production.test.ts	Concurrent tests cover rendered builds, empty builds, exit-code preservation, and ASAN-only VM destruction with leak checks.

Suggested reviewers: jarred-sumner, alii, dylan-conway

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly states that successful bun build --app executions now exit through the build VM.
Description check	✅ Passed	The description explains the problem, fix, impact, verification steps, and retained error behavior in detail.

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[robobun]

^{Updated 6:37 AM PT - Aug 14th, 2026}

✅ @robobun, your commit 4df233892cb8c67b9c37b09b0f2680bb98fc39a8 passed in Build #95732! 🎉

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🧪   To try this PR locally:

bunx bun-pr 38241

That installs a local version of the PR into your bun-38241 executable, so you can run:

bun-38241 --bun

[claude]

LGTM — moves the on_exit() + global_exit() sequence from the JSError arm to run for both success and JS-error paths, matching the exit pattern already used by bun run, the repl, and process.exit().

What was reviewed:

• Confirmed global_exit() -> ! so _vm_guard never fires on the new path (no double-destroy); the Err(e) return still uses the guard as before.
• Checked that on_exit() sets is_shutting_down before global_exit()'s debug assert, and that this exact sequence is the established pattern in run_command.rs / repl_command.rs / node_process.rs.
• The JSError arm's raw (*vm_ptr) derefs are replaced with the safe vm.global() accessor and a single reborrow — strictly less unsafe than before.
• Three new tests cover both success paths (rendered + no-routes) and an ASAN-gated LSan check for the wrapper natives that motivated the fix.

Extended reasoning...

Overview

The PR changes build_command in src/runtime/bake/production.rs so that a successful bun build --app exits through vm.on_exit() + vm.global_exit() instead of returning Ok(()) and letting the scopeguard call only destroy(). The JSError arm already did this; the change hoists the two calls to run after the match for both Ok and JSError. The Err(e) early return (bundler/I/O failure handled by the CLI root) is unchanged. Three tests are added to test/bake/dev/production.test.ts.

Security risks

None. This is process-exit sequencing for a build command; no untrusted input parsing, auth, or crypto is touched.

Level of scrutiny

Medium. VM lifecycle is memory-safety-adjacent, but the change is a small hoist of two calls that were already present in this function's JSError arm and are the standard exit sequence at every other main-thread VM site (run_command.rs:1568/1584, repl_command.rs:220/246, node_process.rs:88). I verified global_exit() returns !, so _vm_guard, _api_lock, and pt never drop on the new path — identical to how the JSError arm already behaved, so no new drop-ordering or double-destroy concern is introduced. The reworked JSError arm reduces the number of unsafe blocks by using the safe vm.global() accessor.

Other factors

Test coverage is strong: the two functional tests assert exact stdout (done\nexit event: N\n) and exit codes for both the rendered path and the no-routes early return, and the ASAN-only test spawns with detect_leaks=1 + BUN_DESTRUCT_VM_ON_EXIT=1 and asserts none of the three leaked types appear in the LSan report (with a comment explaining why it doesn't require an empty report yet). Tests use test.concurrent, spread bunEnv, and reference the shared WAIT_MULTIPLIER — matching harness conventions in the file. The PR description documents that the full file (12/12) passes on a debug ASAN build including the pre-existing throwing-component test that exercises the restructured JSError arm.

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@test/bake/dev/production.test.ts`:
- Around line 683-685: Update the LSAN_OPTIONS assignment in the environment
configuration to preserve and extend bunEnv.LSAN_OPTIONS, appending the existing
suppression settings rather than replacing inherited values. Keep the current
resolved leaksan.supp path and print_suppressions setting unchanged.

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• src/runtime/bake/production.rs
• test/bake/dev/production.test.ts

[claude]

LGTM — extends the existing on_exit + global_exit sequence (already used by the JSError arm and by bun run/bun test) to the success path.

Checked that on_exit() sets is_shutting_down before global_exit()'s debug_assert, and that global_exit() -> ! typechecks as the tail expression. The _api_lock/pt still being live at global_exit() matches the pre-existing JSError-arm behavior, so no new drop-ordering concern. The Err(e) return path is unchanged and remains the only user of _vm_guard. Tests cover both fixed early-return sites (rendered and no-pages) plus the ASAN teardown; the LSan test asserts on report contents rather than exit code, avoiding the flakiness pattern noted in the thread.

Extended reasoning...

Overview

Two files: src/runtime/bake/production.rs restructures the tail of build_command so that both the Ok(()) and Err(JSError) arms of the build_with_vm match fall through to vm.on_exit(); vm.global_exit(), instead of only the JSError arm doing so. The JSError arm now only prints the exception and defaults exit_code to 1. The Err(e) (bundler/I/O failure) arm is unchanged. test/bake/dev/production.test.ts gains three concurrent tests covering the rendered-build path, the no-pages early return, and (ASAN-only) VM teardown under BUN_DESTRUCT_VM_ON_EXIT.

Security risks

None. This is process-exit sequencing for a build tool's dedicated VM; no untrusted-input parsing, auth, or crypto is touched.

Level of scrutiny

Moderate — native runtime code touching VM lifecycle, but the change is essentially "apply the exit sequence the error arm already used to the success arm too". No new mechanism is introduced; on_exit + global_exit is the established main-thread-VM exit used by bun run, bun test, and the repl, and was already the behavior of this function's own error path. I verified global_exit() -> ! (so it typechecks as the tail of a Result<()> function and the scopeguard is correctly unreachable on that path), and that on_exit() sets is_shutting_down to satisfy global_exit's debug assertion. The unsafe { &mut *vm_ptr } reborrow after build_with_vm returns is the same reborrow the old JSError arm did, just hoisted before the match; pt's BackRef isn't dereferenced while it's live.

Other factors

The PR description is unusually thorough — it names the exact leaked types, explains why destroy() alone doesn't free them (JSC-cell-owned natives need heap teardown), documents the interaction with #38233/#38004, and confirms the whole test file (including the pre-existing throwing-component case that exercises the restructured JSError arm) passes on a debug ASAN build. All three comment-cop nags and the CodeRabbit LSAN_OPTIONS-inheritance nit have been addressed and resolved. The tests use WAIT_MULTIPLIER from the bake harness for their timeout budget, matching how the harness scales production-build waits, and the LSan test filters stderr for specific type names rather than requiring exitCode === 0 on a detect_leaks=1 run, which avoids the known flakiness pattern for JSC-cell-owned natives.

[claude]

I reviewed this PR and didn't find any bugs. Because it changes the VM exit/teardown sequence for bun build --app (unsafe reborrows, scopeguard interaction, and a user-visible behavior change where successful builds now honor process.exitCode and run exit handlers), a human look would still be worthwhile.

What was reviewed:

• global_exit() returns !, so _vm_guard/_api_lock/pt never drop on the Ok/JSError paths — matches what the pre-existing JSError arm already did, and the Err(e) return path is unchanged.
• The post-build_with_vm reborrow is the same pattern as before, consolidated; vm is unused in the Err(e) arm so NLL ends its borrow before drops run.
• All three affected paths (rendered success, no-pages early return, restructured JSError arm) have coverage; the ASAN test checks stderr for the specific leaked type names rather than requiring exit 0, avoiding the LSan-in-JSC-heap flakiness pattern.

Extended reasoning...

Overview

This PR moves vm.on_exit() + vm.global_exit() in src/runtime/bake/production.rs::build_command from inside the Err(JSError) match arm to after the match, so successful builds and the no-pages early return also exit through the build VM. The JSError arm is simplified to use vm.global() / vm.print_error_like_object_to_console() through a single reborrow instead of three separate raw-pointer derefs. Three new tests in test/bake/dev/production.test.ts cover the rendered-success path (exit handler + process.exitCode), the no-pages path, and an ASAN-only leak check for wrapper-owned natives. test/no-validate-leaksan.txt gains a comment explaining why the file stays listed.

Security risks

None. No parsing of untrusted input, no network/auth/crypto, no new allocations or ownership transfers.

Level of scrutiny

Medium-high. The Rust change is small (~20 lines) and mechanically hoists code that one match arm already ran, but it sits in VM lifecycle code with unsafe reborrows and a scopeguard whose reachability changes. It also changes user-visible behavior: a successful bun build --app now runs process.on('exit') handlers and exits with process.exitCode instead of unconditionally 0. Bake is experimental, which lowers the blast radius, but VM exit/teardown is exactly the kind of path REVIEW.md flags for careful lifecycle audit.

Other factors

Verified global_exit() is -> ! (src/jsc/VirtualMachine.rs:1679), so the _vm_guard scopeguard is only reached by the unchanged Err(e) => return Err(e) arm, matching the updated comment. The API lock and attached PerThread (with its Strong) are still live when global_exit runs teardown under BUN_DESTRUCT_VM_ON_EXIT — but that was already true for the pre-existing JSError arm and is exercised by the existing throwing-component test in the same file, so it is not a new interaction. The new LSan test asserts on specific type names in stderr rather than exitCode === 0, which sidesteps the known JSC-heap/LSan flakiness. All prior bot comments (comment-cop verbosity, LSAN_OPTIONS inheritance) are resolved. No prior claude[bot] review on this PR. Given the memory-safety-adjacent surface and the user-visible semantic change, deferring for a maintainer glance rather than auto-approving.