Set has_loaded on every path that produces the entry point's source - #33371
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The entry point's has_loaded flag was only set on the path that reaches the printer. When the entry came from the runtime transpiler cache, the // @Bun pragma, or the async-module queue, the flag stayed false and every later module request silently took the "still loading main" branch: require.extensions was never consulted, and unknown-extension ESM imports were parsed as TSX instead of using the file loader. Because the transpiler cache only stores files >= 4 KiB, the same script behaved differently on a cold cache than on a warm one.
StatusReproduced on stock 1.4.0 and on Verification of the three new tests on the current tree (
The two cache tests were updated in fbc87c4 because Adjacent suites unchanged: Review threads are all addressed. CI for fbc87c4 is running. Sequencing note: #32177 carries a cache-hit-only version of this as an incidental hunk; whichever lands second should drop the overlap. |
WalkthroughMoves the Changeshas_loaded fix and loader regression coverage
Possibly related PRs
Suggested reviewers: 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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This PR may be a duplicate of:
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Re the duplicate-detector: #32177 does carry a narrow version of this, but only as an incidental hunk inside a 716-line implicit-strict-mode change, and it only patches the transpiler-cache-hit branch: // inside the `if let Some(entry_ptr) = cache.entry.take()` arm
if is_main {
unsafe { (*jsc_vm).has_loaded = true };
}That leaves the rest of the class unfixed. The cache hit is one of several returns that produce the entry point's source without reaching the printer, and each of the others loses the flag the same way:
This PR hoists the assignment to a single point after the entry's parse succeeds so every one of those paths is covered, and adds regression tests for the cache-hit and pre-bundled shapes. It is 12 lines in one file and does not depend on the strict-mode work. If #32177 lands first, its |
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The reasoning and tests look solid to me, but this moves a state transition inside the core module-loading path (Bun__transpileFile → transpile_source_code_inner) that every entry point flows through, so it's worth a human confirming the new placement and the added !disable_transpilying guard — plus deciding how to sequence with #32177's overlapping hunk.
Extended reasoning...
Overview
This PR moves the (*jsc_vm).has_loaded = true assignment in transpile_source_code_inner (src/runtime/jsc_hooks.rs) from after the printer to right after the entry's parse succeeds, so it fires on every path that produces the entry point's source — cache hit, // @bun pragma, JSON/TOML, empty .cjs, and the async-module queue — instead of only the printed path. It adds a !disable_transpilying guard to exclude source-print-only fetches. Three regression tests are added covering the transpiler-cache warm-hit case (both require.extensions and unknown-extension ESM imports) and the pre-bundled // @bun @bun-cjs entry case.
I traced the readers of has_loaded (jsc_hooks.rs:4182-4241) and confirmed they gate exactly what the PR description claims: concurrent transpiler dispatch, require.extensions consultation, and the unknown-extension → file-loader fallback. Nothing between the new and old assignment locations reads the flag, and the recursive re-entry at line ~2505 happens before the new location, so there's no premature observation. The !disable_transpilying guard is behavior-preserving relative to the old code, since the disable_transpilying branch returned before ever reaching the old assignment.
Security risks
None. This is a boolean state flag controlling loader selection within the same process; no auth, crypto, path traversal, or untrusted-input parsing is involved.
Level of scrutiny
High. The net native change is only ~9 lines, but it sits in Bun__transpileFile's inner path — every bun <entry> invocation flows through here, and has_loaded gates three separate downstream behaviors. Getting the placement subtly wrong (e.g., setting it before a path that shouldn't count as "entry loaded") would change module resolution for arbitrary user code. The fix looks correct to me, but blast-radius alone makes this worth a maintainer's eyes rather than a bot approval.
Other factors
- The tests are well-constructed: they assert cache write on run 1 and cache hit on run 2 via
newCacheCount(), and use distinguishable outputs ("custom-loader" vs "default-loader") so a bypass produces a wrong value rather than a silent pass. The author verified they fail onmainand pass with the fix. - There is an overlapping open PR (#32177) that patches only the cache-hit branch as a side-fix inside a larger change; the author has already commented on how to reconcile them, but a maintainer should decide the landing order.
- No CODEOWNERS file exists in this repo, and no human reviewer has commented yet.
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To make confirming the placement cheap, here is every Both reads sit at the top of
Between the new position and the old one, the only calls are On
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The '// @Bun' tests in runtime-transpiler.test.ts fail on a second release-build run when the entry module is served from the runtime transpiler cache (the has_loaded flag is not set on that path; #33371 tracks it). Keep that file untouched and put the class-hoist TDZ tests in a sibling file so they can be verified independently. Also document that the use_count_estimate guard counts textual mentions in already-visited statements (including function bodies), and extend the 'still hoisted' test to pin that a class mentioned by a preceding function body is left in source order while an unmentioned class is still moved ahead.
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Inline comments:
In `@test/cli/run/transpiler-cache.test.ts`:
- Around line 272-278: Update the affected test callbacks around the bunRun
calls to be async, await both bunRun(join(temp_dir, "entry.js"), env) results,
and perform stdout and newCacheCount() assertions only after each awaited
process completes; apply the same change to the additional occurrence near the
second referenced test block.
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📒 Files selected for processing (3)
src/runtime/jsc_hooks.rstest/cli/run/run-cjs.test.tstest/cli/run/transpiler-cache.test.ts
bunRun() became async on main after this branch was opened, so the two new transpiler-cache tests were reading .stdout off a promise. Use the file's current toSpawn() idiom, which also checks exit code and stderr.
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LGTM — the missing await on bunRun() is fixed in fbc87c4 and the tests now match the file's toSpawn() idiom.
What was reviewed:
- Hoisting
has_loaded = trueabove the cache-hit /// @bun/ async-queue early returns intranspile_source_code_inner; confirmed the two readers (concurrent-store dispatch and unknown-extension loader fallback intranspile_file) sit before this function is entered, so nothing between the new and old positions can observe the flag mid-call. - The
!disable_transpilyingguard is behavior-preserving — the old assignment sat after thedisable_transpilyingreturn, so print-only fetches never set the flag before either. - New tests:
bunRunis now awaited,newCacheCount()asserts a real write on run 1 and a hit on run 2, and therun-cjstest drains stdout/stderr concurrently withexited.
The sequencing note with #32177 is for whoever lands second; it doesn't affect this diff.
Extended reasoning...
Overview
Moves (*jsc_vm).has_loaded = true from after the printer in transpile_source_code_inner (src/runtime/jsc_hooks.rs) to immediately after the entry's parse succeeds, so every early return that produces the entry point's source — runtime-transpiler-cache hit, // @bun / // @bun @bun-cjs pragma, the async-module queue, and the raw-JSON/data-format paths — sets the flag. Adds three regression tests: two in test/cli/run/transpiler-cache.test.ts (cache cold vs. warm for require.extensions and for the unknown-extension file loader) and one in test/cli/run/run-cjs.test.ts (a pre-bundled CJS entry with the cache disabled).
Security risks
None. This is a boolean state flag governing loader selection for subsequent module fetches; no untrusted input parsing, no auth/crypto/permissions surface, no new unsafe blocks (the two unsafe { (*jsc_vm)... } derefs use the same per-fn-contract SAFETY justification as the surrounding code and as the removed block).
Level of scrutiny
Moderate. Module loading is a hot, critical path, but the change is a 7-add/5-remove relocation of one assignment inside one function. I traced every reader of has_loaded: the two reads in transpile_file (jsc_hooks.rs:4565–4575 for concurrent-store dispatch, :4625–4627 for the unknown-extension/require.extensions fallback) both execute before transpile_source_code_inner is entered, and the only two writers besides this one are the = false resets in VirtualMachine::reload_entry_point{,_for_test_runner}. Between the new position and the old one, the code path is: JSON return, disable_transpilying return, data-format exports, already_bundled, empty-CJS, cache hit, async enqueue, linker, printer — none of which re-enter transpile_file synchronously (the PR author separately noted that macro expansion, the one nested-transpile case, runs inside the parse call before the new assignment). The !disable_transpilying guard exactly preserves the old behavior for print-only fetches, which returned before the old assignment site.
Other factors
- My prior review flagged that the two new cache tests called
bunRun()withoutawaitafterbunRunbecame async onmain; fbc87c4 fixes this and adopts theexpect(await bunRun(...)).toSpawn(...)idiom the rest of the file uses (which also asserts exit 0 and empty stderr). I confirmedbunRunintest/harness.ts:503is async andtoSpawnat :711 checks exitCode/stderr/stdout. - The comment-cop bot's paragraph-comment complaint was addressed by trimming to two lines; the remaining comment states placement rationale, not a workaround.
- Tests assert the cache was actually written (
newCacheCount() === 1) and then hit (=== 0), so they can't pass by accident with caching disabled. Therun-cjstest usesPromise.allto drain both pipes withexitedand asserts a combined{stdout, exitCode}object. - The overlap with #32177 (which patches only the cache-hit branch) is documented; whichever lands second drops the redundant hunk. That's a sequencing decision, not a correctness concern for this diff.
Entries are now always loaded as a string in the width they were written in, so the OutputCode enum's UTF-8 byte variant, the transcoding arms that consumed it and the unwritten UTF8 tag constant have no remaining uses. The debug source dump writes cached entries out as UTF-8 the same way it does freshly printed modules. Also drop the has_loaded assignments and tests that came in with the // @Bun UTF-8 change; main now sets the flag once before every early return (#33371).
Main now sets has_loaded before the cache-hit early return (with a comment naming that path), and its test suite already covers unknown-extension loading after a cached entry point, so both the write and the duplicate test are dead.
2 participants
Fixes #35553
Fixes #34437
Repro
entry.jsis 7.5 KiB (anything at or above the transpiler cache's 4 KiBMINIMUM_CACHE_SIZE) and registers arequire.extensionshook:with
asset.datacontainingmodule.exports = "default-loader";Same script, same contents, different behavior on the second run.
BUN_RUNTIME_TRANSPILER_CACHE_PATH=0makes it go away, as does dropping the file below 4 KiB.The ESM half is a hard error rather than a silent fallback:
The unknown extension should go through the file loader; on a cache hit it is parsed as TSX.
Cause
VirtualMachine.has_loadedmeans "the entry point's source has been produced", and three decisions inBun__transpileFileare gated on it:require.extensionsis consulted for a non-built-in extension,.ts(CJS) or is parsed as TSX.transpile_source_code_inneronly set the flag on the path that reaches the printer. Every earlierreturnfor the main module left itfalse:// @bun/// @bun @bun-cjsalready-bundled pragma (whatbun build --target=bun --format=cjsemits),resume_loading_modulelinks and prints directly, and never sets the flag).So a bundled CJS entry point reproduces the same bypass with no cache involved at all:
This is long-standing; it reproduces on 1.4.0 and on
main.Fix
Set
has_loadedonce, right after the entry's parse succeeds, before any of the branch-specific returns, and drop the late assignment after the printer.disable_transpilyingfetches are excluded because they are source-print requests (Bun.inspect(new Error)), not module loads.Verification
test/cli/run/transpiler-cache.test.ts: the entry point is run twice, cold then warm;require.extensionsmust fire both times, and an unknown-extension ESM import must use the file loader both times. Both assert the cache was written on run 1 and hit on run 2 via the existingnewCacheCount()helper. (Runtime transpiler cache causes unknown-extension ESM imports to use the TSX loader on a warm cache #34437 / #34437 remains reproducible: warm transpiler-cache hit uses the TSX loader for unknown-extension ESM imports #35553 are the second of these with an.svgin place of.someext.)test/cli/run/run-cjs.test.ts: a// @bun @bun-cjsentry point consultsrequire.extensions.With
src/runtime/jsc_hooks.rsreplaced by themaincopy, exactly those three tests fail (3 fail / 12 pass across the two files); with the fix, 15 / 15 pass. Re-checked aftermainwas merged in (0cf32a5).test/cli/run/,test/js/node/module/,test/cli/hot/hot.test.ts,test/cli/test/isolation.test.tsandtest/regression/issue/30887.test.tsare otherwise unchanged.Previous verification note (before the merge of main)
test/cli/run/transpiler-cache.test.ts: the entry point is run twice, cold then warm;require.extensionsmust fire both times, and an unknown-extension ESM import must use the file loader both times. Both assert the cache was actually written on run 1 and hit on run 2 via the existingnewCacheCount()helper.test/cli/run/run-cjs.test.ts: a// @bun @bun-cjsentry point consultsrequire.extensions.All three fail on
mainand pass with this change.test/cli/run/,test/js/node/module/,test/cli/hot/hot.test.ts,test/cli/test/isolation.test.tsandtest/regression/issue/30887.test.tsare otherwise unchanged.Fixes #34437
Fixes #35553
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