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runMain() with no argument coerced `undefined` to the string "undefined" and tried to resolve it as a module, throwing `Cannot find package 'undefined' from ''`. Node defaults the argument to the main entry point (`function executeUserEntryPoint(main = process.argv[1])`), so a bare `runMain()` re-runs the already-loaded main module, which is a no-op. Default the argument to `process.argv[1]` when none is passed. Closes #31773
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Updated 8:21 PM PT - Sep 1st, 2026
✅ @robobun, your commit acb221ef2a6c54c8b3a10dbb924b1ad11f1bfb67 passed in 🧪 To try this PR locally: bunx bun-pr 41147That installs a local version of the PR into your bun-41147 --bun |
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Module.runMain default entry resolution
Suggested reviewers: Merge Risk: ⚪ Minimal · up to This change defaults no-argument runMain() calls to process.argv[1] and validates explicit arguments consistently with Node; no actionable merge-blocking risk remains beyond normal checks and review. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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…ment Node's default parameter only substitutes undefined. Any other non-string value reaches path.resolve(main), which throws ERR_INVALID_ARG_TYPE for "paths[0]". Match that instead of coercing null or a number to a module specifier string.
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Inline comments:
In `@src/jsc/modules/NodeModuleModule.cpp`:
- Around line 793-796: Update jsFunctionRunMain to always perform the JSC
JSValue property access for process.argv via get(globalObject, 1u), removing the
argv.isObject() guard so strings are boxed and nullish values preserve
property-access TypeErrors; add subprocess coverage for replaced string and null
argv values.
In `@test/js/node/module/node-module-module.test.js`:
- Around line 924-928: Update the runMain() invalid-argument parameter matrix
from test.each() to describe.each(), and place a single test() inside each
generated suite while preserving the existing cases and assertions.
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LGTM — thanks for addressing both earlier notes: the non-string check now covers null/numbers/objects (with matching test.each cases and the rewritten no-coercion test), and the -e test now drains stdout alongside stderr.
What was reviewed:
jsFunctionRunMain:getArgv/indexedgetboth guarded byRETURN_IF_EXCEPTION;!isString()gate placed after the argv default so a missing/non-stringprocess.argv[1]and explicit non-string args both hitERR_INVALID_ARG_TYPEwithout ever reachingtoWTFStringcoercion.- Tests: ESM/CJS re-entry,
-ewith no argv[1], null/number args, and a non-arrayprocess.argvreplacement — all spawn withbunEnv/tempDir, drain stdout+stderr+exited concurrently, and assert output before exit code.
Extended reasoning...
Overview
This PR changes jsFunctionRunMain in src/jsc/modules/NodeModuleModule.cpp so that Module.runMain() with no argument defaults to process.argv[1] (matching Node's executeUserEntryPoint(main = process.argv[1])) instead of coercing undefined to the literal string "undefined" and failing resolution. The latest commit (bc05c93) additionally rejects any non-string argument with ERR_INVALID_ARG_TYPE("paths[0]", "string", ...), mirroring Node's path.resolve(main) validation inside resolveMainPath. Tests in test/js/node/module/node-module-module.test.js were extended to cover ESM and CJS re-entry, -e with no argv[1], null/number arguments, and a plain-object replacement of process.argv. The pre-existing "propagates an error from stringifying" test was rewritten to assert the new type-check-before-coercion semantics.
Security risks
None. This is a Node compatibility fix to argument defaulting/validation in node:module's runMain. It reads process.argv via the process object's own accessor and an indexed get; both calls are followed by RETURN_IF_EXCEPTION. No new I/O, no untrusted parsing, no auth/crypto surface.
Level of scrutiny
Low-to-moderate. The C++ change is ~15 lines with straightforward control flow and correct exception-scope handling per REVIEW.md's "Exception checks after every call that can enter JS" rule. The !arg1.isString() gate makes the subsequent toWTFString a no-throw string unwrap (still guarded). Bun's own startup passes an explicit specifier to runMain, so only user-initiated no-arg/non-string calls change behavior.
Other factors
Both inline comments from the prior review round were fully addressed by bc05c93: (1) the undrained stdout: "pipe" in the -e test is now read in Promise.all and asserted empty; (2) the undefined-only guard was widened to !isString() with new tests for null and numbers. There are no outstanding CHANGES_REQUESTED reviews or unresolved third-party objections in the timeline. Test conventions (tempDir with using, bunExe/bunEnv, concurrent pipe draining, output-before-exit-code assertions, test.each for the variant matrix) match harness guidance.
Node reads the default through process.argv[1], a JS property access on whatever process.argv is. Remove the isObject guard: a replaced string indexes, and null or undefined throw a TypeError at the access, like Node. Tests cover an array-like object, a string, and null.
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LGTM — both earlier points (draining stdout in the -e test, and rejecting non-string args with ERR_INVALID_ARG_TYPE before coercion) are addressed, and the switch to a plain argv.get(globalObject, 1u) now matches Node's property-access semantics for replaced process.argv.
What was reviewed:
- Exception-scope handling in
jsFunctionRunMain:RETURN_IF_EXCEPTIONfollows bothgetArgv()andargv.get(), and the!isString()guard runs beforetoWTFString, so a throwingtoStringis never reached. Process::getArgvreturns the user-setm_argv(via theprocess.argvcustom setter), so the array-like / string / null replacement tests exercise the real path;JSValue::getonjsNull()throws the property-access TypeError the test expects.- Tests: all three
describe.eachsuites drain stdout/stderr/exited concurrently, assert content before exit code, usetempDir/bunExe/bunEnv/await using, and the"x/"[1]case picks an absolute path to stay offline.
Extended reasoning...
Overview
This PR changes jsFunctionRunMain in src/jsc/modules/NodeModuleModule.cpp to default the main argument to process.argv[1] when called with undefined, and to throw ERR_INVALID_ARG_TYPE for "paths[0]" when the resulting value is not a string — matching Node's executeUserEntryPoint(main = process.argv[1]) → path.resolve(main) path. The test file gains three describe.each suites covering ESM/CJS no-arg re-entry, -e/null/number invalid-arg cases, and replaced process.argv (array-like, string, null). One pre-existing test that asserted toString() throw propagation was updated to expect the type-check error instead, since Node validates before coercion.
Security risks
None. This is argument-defaulting and validation for a Node-compat entry point that was already callable with an arbitrary string. No new data flows, no auth/crypto/permissions surface, no untrusted parsing added.
Level of scrutiny
Low-to-moderate. The native change is ~16 lines and follows the file's existing exception-scope pattern: RETURN_IF_EXCEPTION after getArgv(globalObject) and after argv.get(globalObject, 1u), then a type guard before toWTFString. I verified Process::getArgv (BunProcess.cpp:3177) returns the stored m_argv value — which is what the process.argv custom setter writes — so the plain JSValue::get correctly reproduces JS property-access semantics (string indexing, TypeError on null) that the new tests assert. The Bun::ERR::INVALID_ARG_TYPE helper is the repo's standard coded-error path.
Other factors
Both inline comments from my earlier review are addressed: every spawned test now drains stdout/stderr/exited via Promise.all, and non-string arguments (null, 42, throwing-toString object) uniformly hit the !arg1.isString() guard with matching test coverage. The latest two commits (75531db, acb221e) tightened the argv read from an isObject()-gated getObject()->get() to a plain JSValue::get, which is both simpler and more Node-accurate, and added the string/null replaced-argv cases. Tests follow test/CLAUDE.md conventions (harness helpers, tempDir, await using, content-before-exit-code assertions, no network). The change is small, self-contained, and well-covered.
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Closes #31773. Supersedes #31774 (same change; that PR was stale-closed and its head branch was renamed, which closed it for good).
Problem
import { runMain } from "node:module"; runMain();throwsCannot find package 'undefined' from ''. Still reproduces on 1.4.1-canary (a6c4cc2).jsFunctionRunMain(src/jsc/modules/NodeModuleModule.cpp) passescallFrame->argument(0)straight totoWTFString(). With no argument that coercesundefinedto the string"undefined", and module resolution fails.Fix
process.argv[1], matching Node'sexecuteUserEntryPoint(main = process.argv[1]). The default is a plain property get, so a replaced array-likeprocess.argvworks like in Node.ERR_INVALID_ARG_TYPEfor"paths[0]", exactly like Node'sresolveMainPath->path.resolve(main). This coversbun -e(noargv[1]),runMain(null), andrunMain(42). Node validatestypeofbefore any coercion, so a throwingtoStringis never called. Verified against node v24.process.argv[1]is the same string as the entry path the module registry already holds, soloadAndEvaluateModulefinds the evaluated main module and the call is a cached no-op.test/js/node/module/node-module-module.test.js(5 new tests plus 1 updated). The no-arg tests fail on the released build with the exact reported error and pass with this change. All 55 runnable tests in the file pass.Background
Module.runMain()is Node's entry-point runner. Calling it with no argument from an already-running script is a documented pattern and a no-op in Node.runMainis also overridable (tools patch it). The override path is unchanged. Bun's own startup always passes an explicit specifier.toStringon the argument propagates. Node throwsERR_INVALID_ARG_TYPEwithout callingtoString, so the test now expects that error. The no-crash intent of that test (Add missing exception checks on module-loading paths #40069) still holds.no test proof · iteration 10 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/module/node-module-module.test.js