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…e object The linker used `exports_foo` of a lifted CommonJS module as both its `module.exports` (what a default import binds) and its `import *` namespace. So `ns === d`, `ns.default` was the lifted `exports.default` instead of `module.exports`, and `Object.keys(ns)` had no `default`. `exports_foo` stays the `module.exports` object. `import * as ns` now binds to `var import_foo = __toESM(exports_foo, 1)`, declared in a part of its own that prints with the namespace export part and is dropped unless the namespace is used as a value. `ns.default` and `ns.x` still bind to `exports_foo` and the lifted bindings directly. A `require()` that `unwrap_commonjs_to_esm` turned into an import star keeps binding `module.exports`. A star import from an importer that is not an ES module by type keeps the CommonJS wrapper of a module that sets both `exports.__esModule` and `exports.default`, as a default import does.
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Updated 10:03 AM PT - Sep 9th, 2026
✅ @robobun, your commit ab35eebc5e55bd4968b2fadd039a7c3819c4a639 passed in 🧪 To try this PR locally: bunx bun-pr 41820That installs a local version of the PR into your bun-41820 --bun |
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…` resolves `default` to `module.exports` The chunk for a split `import()` of a lifted CommonJS module exported the lifted `exports.default` as `default` when the module also assigns `exports.__esModule`, for every importer. Node, esbuild and the build without `--splitting` give `module.exports` to an importer that is an ES module by type. The chunk now always exports `module.exports` as `default`, and an importer that is not an ES module by type unwraps `exports.default` from it through `__toESM(m.default)`, the same per importer rule the unsplit build applies. Also shortens the comments the previous commit added.
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Pushed 9546932:
Reproduced with the ledger repro ( |
…r shapes and flags; pin the user entry point shape (#12463)
robobun
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September 9, 2026 15:41
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Marked ready for review. Since the last comment (5cb06b7, d93da0b):
CI on 5cb06b7: every bundler lane is green; the red jobs are |
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Path: .coderabbit.yaml Review profile: ASSERTIVE Plan: Essentials Run ID: 📒 Files selected for processing (4)
Included review availability: Your plan provides up to 10 included reviews per hour; 6 remain after this review. WalkthroughThe bundler now tracks lifted CommonJS namespace objects separately from ChangesLifted CommonJS namespace interop
Possibly related PRs
Suggested reviewers: Priority: ➖ Normal Merge Risk: 🔵 Low · up to This updates lifted CommonJS namespace interop behavior and adds broad oracle coverage. The remaining risk is limited to potentially flaky or stalled bundler test execution from concurrent subprocesses without timeouts. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Inline comments:
In `@docs/bundler/index.mdx`:
- Line 1418: Correct the importer-type condition in the CommonJS interop
explanation so .mjs, .mts, and packages with "type": "module" are treated as ES
modules by type, preserving the documented exports.default exception for other
importers. Update the corresponding summary-table condition near the same
section to use the same corrected classification.
In `@test/bundler/bundler_cjs2esm.test.ts`:
- Around line 2678-2681: Replace the nested iteration in the parameterized test
matrix with describe.each(Object.entries(libs)) and test.each(cells), preserving
the existing libName, lib, dynamic, flags, lifted, and test-name behavior while
ensuring failing cases report their parameters.
- Line 2681: Update the oracle-cell test declaration using test.concurrent to
pass an explicit 30-second timeout after the test body, preserving the existing
concurrent execution and test logic.
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docs/bundler/index.mdxsrc/bundler/LinkerContext.rssrc/bundler/LinkerGraph.rssrc/bundler/linker_context/doStep5.rssrc/bundler/linker_context/findAllImportedPartsInJSOrder.rssrc/bundler/linker_context/generateCodeForFileInChunkJS.rssrc/bundler/linker_context/scanImportsAndExports.rstest/bundler/bundler_cjs.test.tstest/bundler/bundler_cjs2esm.test.tstest/bundler/esbuild/dce.test.tstest/bundler/esbuild/importstar.test.tstest/bundler/esbuild/importstar_ts.test.ts
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…ed-cjs-namespace-default
…atever exports.__esModule says; run the oracle cells with async spawns
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Pushed 2aeb756 (merge of main) and ab35eeb:
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…default import as a value (#42569) ### Problem - Since #41162 (1.4.1), `import lib from "./lib.cjs"` of a lifted CommonJS module is a namespace object with a getter and a setter per export. `Object.defineProperty(lib, "x", ...)` and `delete lib.y` change that object, but `lib.x` reads the lifted `$x` binding. A write after `Object.freeze(lib)` still runs the setter. - Node, `bun run` and 1.4.0 print `defineProperty -> 65`, `delete -> true undefined false`, `write to frozen -> 3 true`. The bundle prints `1`, `true 2 false`, `66 true`. - Source: a fuzz ledger that compares bundles with `bun run`. No user issue reports this. ### Fix - The parser sets a new symbol flag, `import_used_as_value`, on an import that some use holds as a value. Exempt: a read, call or assignment of a property (`X.a`, `X[k]`, `X.a = 1`) and a destructuring declaration. `delete X.a` counts. - Step 1 of `scan_imports_and_exports` keeps the `__commonJS` wrapper of a lifted module when a default import of it has the flag or is re-exported. The importer gets the real `module.exports`, as in 1.4.0. - `React.useState()` and `React.x = y` stay lifted: react 18.3.1 `--production --minify` is 1423 bytes, same as main. With `Object.keys(React)` it is 7219 bytes (main 7794). - Verified: `test/bundler/bundler_cjs2esm.test.ts` (11 new cases fail on main), plus the suites in the Notes. ### Background - Lifting turns `exports.foo = x` into `var $foo = x` plus an ES module export. - The namespace object `exports_lib` stands in for `module.exports`. `__exportCjs` (#41182) gives it a getter and a setter per export. - `defineProperty` and `delete` only replace or remove the accessor. A frozen accessor still calls its setter. - Step 1 picks the CommonJS files before imports are matched, so it has parser facts only. A re-export counts as held. <details><summary>Notes</summary> Output for the report's repro is now byte-identical to what 1.4.0 emits (`var import_lib = __toESM(require_lib(), 1); Object.defineProperty(import_lib.default, "x", ...)`). How the flag is computed: `e_dot` and `e_index` visit their target with `ExprIn::is_property_access_target` (false for a delete target), `visit_decls` does the same for the initializer of an object pattern, and `handle_identifier` sets the flag when it turns an identifier into an `EImportIdentifier` without it. Two places build an import identifier outside the visitor and pass the bit themselves: the classic JSX factory (`React.createElement`) and `emitDecoratorMetadata` (`design:type` gets the import itself, so it sets the flag). Dead control flow does not set the flag. The flag is per file: a use in a part that tree shaking later removes still counts. Routes to `module.exports` of a module that stays lifted that this PR does not close. 1.4.0 kept the wrapper for every default import, so when the bundle also has a static default import of the module, these gave the real object in 1.4.0 and give the namespace object here: - `this` in a method call. `lib.self()` with `exports.self = function () { return this; }` still gets the namespace object (#41162 chose that for `this._helper()` style code). - `(await import(m)).default`, same chunk or split. - `ns.default` on `import * as ns` (new in 1.4.1, #41820 reworks it). `require()` of a lifted module outside the react family already keeps the wrapper. A react-family file of the shape `sideEffect(); module.exports = require("./impl")` (react-dom/index.js) is lifted to `export * from "./impl"`. When it keeps its wrapper it prints `module.exports = exports_impl`, the namespace object of `./impl`, as 1.4.0 did. Every read then goes through that object, so `defineProperty` and `delete` work (react-dom 18.3.1 `--production`: `Object.defineProperty(ReactDOM, "version", { value: "dp" })` prints `dp`, as 1.4.0 does, and main prints the old version). A write after `Object.freeze` still reaches the binding there. An earlier commit of this PR also wrapped `./impl`. That gave `module.exports = __toESM(require_impl())`, whose getters are not configurable, so `defineProperty` threw. It is reverted. The real fix for that shape is to print the raw `require_impl()` (handed off, #35722 had the approach). #41820 is open and edits the same step 1 lines, the same docs paragraph and the same tests. This PR is the smaller one and restores 1.4.0 output, so it is simpler to land it first and rebase #41820. Test expectations that changed, all toward Node: - `cjs/__toESM_mixed_import_styles` is back to its expectation from before #41162 (the namespace has a `default` key). - `ReExportDefaultAsNameFromLiftedCommonJS` and `ExportDefaultOfLiftedCommonJSDefaultImport` now keep the wrapper (a re-export can reach an importer that holds the object) and also check `Object.freeze` through the barrel. A third form, `export { React as R }`, is added. - `DefaultImportEscapingKeepsAssignmentOrder` became `DefaultImportPassedAsValueKeepsAssignmentOrder` and expects the wrapper. - Ten tests compared the default import by identity (`m.default === React`) or passed it to `Object.keys`. They now compare a property (`m.default.useState === React.useState`) so that they keep testing the lifted path. Suites run with the debug build: `bundler_cjs2esm`, `bundler_cjs`, `esbuild/importstar`, `esbuild/importstar_ts`, `esbuild/default`, `esbuild/dce`, `esbuild/splitting`, `esbuild/packagejson`, `esbuild/ts`, `bundler_splitting`, `bundler_edgecase`, `bundler_jsx`, `bundler_npm`, `bundler_barrel`, `bundler_minify`, `bundler_browser`, `bundler_bun`, `bundler_plugin`, `bundler_loader`, `bundler_string`, `bundler_promiseall_deadcode`, `transpiler/transpiler`, `regression/issue/03844`, `bun-build-api` (two bytecode stress tests time out at 5 s under the debug build, they bundle no imports). </details> <!-- robobun:evidence:begin --> --- **[human-review]** gate passed · iteration 0 · 10 files touched <details><summary>fails on main (without fix)</summary> ```console ASAN without fix: 12 FAILED $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/bundler/bundler_cjs.test.ts "test/bundler/bundler_cjs2esm.test.ts" bun test v1.4.3 (b993710) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [1254.52ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [548.64ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [554.77ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [472.17ms] (pass) bundler > cjs2esm/ExportsFunction [398.00ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [505.22ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [490.55ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [561.72ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [617.95ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [686.37ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [551.89ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [704.70ms] (pass) bundler > cjs2esm/ModuleExp ... (truncated) release without fix: 12 FAILED bun test v1.4.3-canary.1 (b993710) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [29.48ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [14.24ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [13.88ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [13.68ms] (pass) bundler > cjs2esm/ExportsFunction [14.09ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [13.74ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [13.08ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [16.07ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [17.11ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [15.81ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [15.04ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [17.65ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvDevelopment [15.90ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRuntimeCondition [16.27ms] (pass) bundler > cjs2esm/UnwrappedModuleRequireAssigned [15.69ms] (pass) bundler > cjs2esm/Unwrap ... (truncated) ``` </details> <details><summary>passes on PR (with fix)</summary> ```console ASAN with fix: all passed $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/bundler/bundler_cjs.test.ts "test/bundler/bundler_cjs2esm.test.ts" bun test v1.4.3 (b993710) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [1115.42ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [521.71ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [536.01ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [594.49ms] (pass) bundler > cjs2esm/ExportsFunction [501.50ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [632.29ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [418.24ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [456.28ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [591.53ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [603.73ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [546.68ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [667.62ms] (pass) bundler > cjs2esm/ModuleExp ... (truncated) release with fix: all passed $ bun scripts/build.ts --profile=release [configured] bun-profile → bun (stripped) target linux-x64-gnu build type Release build dir ./build/release revision b9ce20b features baseline 23 deps, 131 codegen, 1176 objects in 676ms ninja: Entering directory `/workspace/bun/build/release' [1/1248] install /workspace/bun bun install v1.4.3-canary.1 (b993710) Checked 22 installs across 61 packages (no changes) [14.00ms] [2/1248] gen ErrorCode+*.h [3/1248] gen bindgenv2 [4/1248] install /workspace/bun/packages/bun-error bun install v1.4.3-canary.1 (b993710) Checked 1 install across 2 packages (no changes) [2.00ms] [5/1248] install /workspace/bun/src/node-fallbacks bun install v1.4.3-canary.1 (b993710) Checked 111 installs across 104 packages (no changes) [5.00ms] [6/1248] fetch zlib [zlib] up to date [7/1248] gen node-fallbacks/react-refresh.js Bundled 1 module in 10ms react-refresh.js 4.81 KB (entry point) [8/1248] fetch libjpeg-turbo [libjpeg-turbo] up to date [9/1248] fetch tinycc [tinycc] up to date [10/1247] gen .bind.ts → GeneratedBindings.cpp [11/1247] gen bake.{client,server,error}.js -> bake.client.js, bake.serve ... (truncated) ``` </details> <details><summary>diff hotspot</summary> ``` docs/bundler/index.mdx | 2 +- src/ast/symbol.rs | 4 + .../linker_context/scanImportsAndExports.rs | 28 +- src/js_parser/fold.rs | 3 + src/js_parser/p.rs | 19 +- src/js_parser/parser.rs | 14 + src/js_parser/visit/mod.rs | 2 + src/js_parser/visit/visit_expr.rs | 18 +- test/bundler/bundler_cjs.test.ts | 8 +- test/bundler/bundler_cjs2esm.test.ts | 318 +++++++++++++++------ 10 files changed, 318 insertions(+), 98 deletions(-) ``` </details> **gate history** · 1 passed · 0 rejected · iteration 0 <details><summary>evidence per changed file</summary> ``` file reads edits tests docs/bundler/index.mdx 2 2 25 src/ast/symbol.rs 1 2 25 src/bundler/linker_context/scanImportsAndExports.rs 6 10 25 src/js_parser/fold.rs 1 1 25 src/js_parser/p.rs 7 6 25 src/js_parser/parser.rs 2 4 25 src/js_parser/visit/mod.rs 1 1 25 src/js_parser/visit/visit_expr.rs 5 3 25 test/bundler/bundler_cjs.test.ts 1 2 9 test/bundler/bundler_cjs2esm.test.ts 11 18 20 ``` </details> <!-- robobun:evidence:end -->
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Sep 15, 2026
…default import as a value (oven-sh#42569) ### Problem - Since oven-sh#41162 (1.4.1), `import lib from "./lib.cjs"` of a lifted CommonJS module is a namespace object with a getter and a setter per export. `Object.defineProperty(lib, "x", ...)` and `delete lib.y` change that object, but `lib.x` reads the lifted `$x` binding. A write after `Object.freeze(lib)` still runs the setter. - Node, `bun run` and 1.4.0 print `defineProperty -> 65`, `delete -> true undefined false`, `write to frozen -> 3 true`. The bundle prints `1`, `true 2 false`, `66 true`. - Source: a fuzz ledger that compares bundles with `bun run`. No user issue reports this. ### Fix - The parser sets a new symbol flag, `import_used_as_value`, on an import that some use holds as a value. Exempt: a read, call or assignment of a property (`X.a`, `X[k]`, `X.a = 1`) and a destructuring declaration. `delete X.a` counts. - Step 1 of `scan_imports_and_exports` keeps the `__commonJS` wrapper of a lifted module when a default import of it has the flag or is re-exported. The importer gets the real `module.exports`, as in 1.4.0. - `React.useState()` and `React.x = y` stay lifted: react 18.3.1 `--production --minify` is 1423 bytes, same as main. With `Object.keys(React)` it is 7219 bytes (main 7794). - Verified: `test/bundler/bundler_cjs2esm.test.ts` (11 new cases fail on main), plus the suites in the Notes. ### Background - Lifting turns `exports.foo = x` into `var $foo = x` plus an ES module export. - The namespace object `exports_lib` stands in for `module.exports`. `__exportCjs` (oven-sh#41182) gives it a getter and a setter per export. - `defineProperty` and `delete` only replace or remove the accessor. A frozen accessor still calls its setter. - Step 1 picks the CommonJS files before imports are matched, so it has parser facts only. A re-export counts as held. <details><summary>Notes</summary> Output for the report's repro is now byte-identical to what 1.4.0 emits (`var import_lib = __toESM(require_lib(), 1); Object.defineProperty(import_lib.default, "x", ...)`). How the flag is computed: `e_dot` and `e_index` visit their target with `ExprIn::is_property_access_target` (false for a delete target), `visit_decls` does the same for the initializer of an object pattern, and `handle_identifier` sets the flag when it turns an identifier into an `EImportIdentifier` without it. Two places build an import identifier outside the visitor and pass the bit themselves: the classic JSX factory (`React.createElement`) and `emitDecoratorMetadata` (`design:type` gets the import itself, so it sets the flag). Dead control flow does not set the flag. The flag is per file: a use in a part that tree shaking later removes still counts. Routes to `module.exports` of a module that stays lifted that this PR does not close. 1.4.0 kept the wrapper for every default import, so when the bundle also has a static default import of the module, these gave the real object in 1.4.0 and give the namespace object here: - `this` in a method call. `lib.self()` with `exports.self = function () { return this; }` still gets the namespace object (oven-sh#41162 chose that for `this._helper()` style code). - `(await import(m)).default`, same chunk or split. - `ns.default` on `import * as ns` (new in 1.4.1, oven-sh#41820 reworks it). `require()` of a lifted module outside the react family already keeps the wrapper. A react-family file of the shape `sideEffect(); module.exports = require("./impl")` (react-dom/index.js) is lifted to `export * from "./impl"`. When it keeps its wrapper it prints `module.exports = exports_impl`, the namespace object of `./impl`, as 1.4.0 did. Every read then goes through that object, so `defineProperty` and `delete` work (react-dom 18.3.1 `--production`: `Object.defineProperty(ReactDOM, "version", { value: "dp" })` prints `dp`, as 1.4.0 does, and main prints the old version). A write after `Object.freeze` still reaches the binding there. An earlier commit of this PR also wrapped `./impl`. That gave `module.exports = __toESM(require_impl())`, whose getters are not configurable, so `defineProperty` threw. It is reverted. The real fix for that shape is to print the raw `require_impl()` (handed off, oven-sh#35722 had the approach). oven-sh#41820 is open and edits the same step 1 lines, the same docs paragraph and the same tests. This PR is the smaller one and restores 1.4.0 output, so it is simpler to land it first and rebase oven-sh#41820. Test expectations that changed, all toward Node: - `cjs/__toESM_mixed_import_styles` is back to its expectation from before oven-sh#41162 (the namespace has a `default` key). - `ReExportDefaultAsNameFromLiftedCommonJS` and `ExportDefaultOfLiftedCommonJSDefaultImport` now keep the wrapper (a re-export can reach an importer that holds the object) and also check `Object.freeze` through the barrel. A third form, `export { React as R }`, is added. - `DefaultImportEscapingKeepsAssignmentOrder` became `DefaultImportPassedAsValueKeepsAssignmentOrder` and expects the wrapper. - Ten tests compared the default import by identity (`m.default === React`) or passed it to `Object.keys`. They now compare a property (`m.default.useState === React.useState`) so that they keep testing the lifted path. Suites run with the debug build: `bundler_cjs2esm`, `bundler_cjs`, `esbuild/importstar`, `esbuild/importstar_ts`, `esbuild/default`, `esbuild/dce`, `esbuild/splitting`, `esbuild/packagejson`, `esbuild/ts`, `bundler_splitting`, `bundler_edgecase`, `bundler_jsx`, `bundler_npm`, `bundler_barrel`, `bundler_minify`, `bundler_browser`, `bundler_bun`, `bundler_plugin`, `bundler_loader`, `bundler_string`, `bundler_promiseall_deadcode`, `transpiler/transpiler`, `regression/issue/03844`, `bun-build-api` (two bytecode stress tests time out at 5 s under the debug build, they bundle no imports). </details> <!-- robobun:evidence:begin --> --- **[human-review]** gate passed · iteration 0 · 10 files touched <details><summary>fails on main (without fix)</summary> ```console ASAN without fix: 12 FAILED $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/bundler/bundler_cjs.test.ts "test/bundler/bundler_cjs2esm.test.ts" bun test v1.4.3 (b993710) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [1254.52ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [548.64ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [554.77ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [472.17ms] (pass) bundler > cjs2esm/ExportsFunction [398.00ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [505.22ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [490.55ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [561.72ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [617.95ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [686.37ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [551.89ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [704.70ms] (pass) bundler > cjs2esm/ModuleExp ... (truncated) release without fix: 12 FAILED bun test v1.4.3-canary.1 (b993710) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [29.48ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [14.24ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [13.88ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [13.68ms] (pass) bundler > cjs2esm/ExportsFunction [14.09ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [13.74ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [13.08ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [16.07ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [17.11ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [15.81ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [15.04ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [17.65ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvDevelopment [15.90ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRuntimeCondition [16.27ms] (pass) bundler > cjs2esm/UnwrappedModuleRequireAssigned [15.69ms] (pass) bundler > cjs2esm/Unwrap ... (truncated) ``` </details> <details><summary>passes on PR (with fix)</summary> ```console ASAN with fix: all passed $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/bundler/bundler_cjs.test.ts "test/bundler/bundler_cjs2esm.test.ts" bun test v1.4.3 (b993710) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [1115.42ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [521.71ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [536.01ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [594.49ms] (pass) bundler > cjs2esm/ExportsFunction [501.50ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [632.29ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [418.24ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [456.28ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [591.53ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [603.73ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [546.68ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [667.62ms] (pass) bundler > cjs2esm/ModuleExp ... (truncated) release with fix: all passed $ bun scripts/build.ts --profile=release [configured] bun-profile → bun (stripped) target linux-x64-gnu build type Release build dir ./build/release revision b9ce20b features baseline 23 deps, 131 codegen, 1176 objects in 676ms ninja: Entering directory `/workspace/bun/build/release' [1/1248] install /workspace/bun bun install v1.4.3-canary.1 (b993710) Checked 22 installs across 61 packages (no changes) [14.00ms] [2/1248] gen ErrorCode+*.h [3/1248] gen bindgenv2 [4/1248] install /workspace/bun/packages/bun-error bun install v1.4.3-canary.1 (b993710) Checked 1 install across 2 packages (no changes) [2.00ms] [5/1248] install /workspace/bun/src/node-fallbacks bun install v1.4.3-canary.1 (b993710) Checked 111 installs across 104 packages (no changes) [5.00ms] [6/1248] fetch zlib [zlib] up to date [7/1248] gen node-fallbacks/react-refresh.js Bundled 1 module in 10ms react-refresh.js 4.81 KB (entry point) [8/1248] fetch libjpeg-turbo [libjpeg-turbo] up to date [9/1248] fetch tinycc [tinycc] up to date [10/1247] gen .bind.ts → GeneratedBindings.cpp [11/1247] gen bake.{client,server,error}.js -> bake.client.js, bake.serve ... (truncated) ``` </details> <details><summary>diff hotspot</summary> ``` docs/bundler/index.mdx | 2 +- src/ast/symbol.rs | 4 + .../linker_context/scanImportsAndExports.rs | 28 +- src/js_parser/fold.rs | 3 + src/js_parser/p.rs | 19 +- src/js_parser/parser.rs | 14 + src/js_parser/visit/mod.rs | 2 + src/js_parser/visit/visit_expr.rs | 18 +- test/bundler/bundler_cjs.test.ts | 8 +- test/bundler/bundler_cjs2esm.test.ts | 318 +++++++++++++++------ 10 files changed, 318 insertions(+), 98 deletions(-) ``` </details> **gate history** · 1 passed · 0 rejected · iteration 0 <details><summary>evidence per changed file</summary> ``` file reads edits tests docs/bundler/index.mdx 2 2 25 src/ast/symbol.rs 1 2 25 src/bundler/linker_context/scanImportsAndExports.rs 6 10 25 src/js_parser/fold.rs 1 1 25 src/js_parser/p.rs 7 6 25 src/js_parser/parser.rs 2 4 25 src/js_parser/visit/mod.rs 1 1 25 src/js_parser/visit/visit_expr.rs 5 3 25 test/bundler/bundler_cjs.test.ts 1 2 9 test/bundler/bundler_cjs2esm.test.ts 11 18 20 ``` </details> <!-- robobun:evidence:end -->
Jarred-Sumner
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Sep 26, 2026
…#42549) ### Problem - With `bun build --minify-syntax`, ``ns["tag"]`z` `` prints as ``$tag`z` `` when `tag` is a lifted CommonJS export. The tag then runs with `this === undefined`: `TypeError: undefined is not an object (evaluating 'this._helper')`. ``st["tag"]`z` `` on a default import and ``exports["tag"]`z` `` inside the CommonJS file break too. - The cause is the `a["b"]` to `a.b` rewrite in `e_index` (`src/js_parser/visit/visit_expr.rs:858`). It moves `p.call_target` and `p.delete_target` to the new `E::Dot`, then visits it. It does not move `p.template_tag` (added in #41251). So `e_dot` sees no tag, and the linker binds the export directly. ### Fix - The rewrite also points `p.template_tag` at the new `E::Dot`. esbuild does the same (`p.templateTag = dot`). - The second rewrite in `e_index` (`a["x" + "y"]`) is unchanged. It returns the new `E::Dot` without a visit, so nothing reads the marker. That form already works. - Verified: `test/bundler/bundler_cjs2esm.test.ts` (3 new tests, all fail on main). Also 11 other bundler suites (see the notes). - Self-reviewed: 2 concerns raised, 2 addressed. ### Background - Lifting turns `exports.foo = x` in a CommonJS file into `var $foo = x` plus an ES export. The namespace object (`exports_lib`) stands in for `module.exports`. - ``X.name`z` `` passes `X` as `this`, like a method call. ``$name`z` `` passes `undefined`. #41251 makes the linker keep `X.name` as written when the file calls it or tags a template with it. - `e_template` stores the tag node in `p.template_tag`. `e_dot` and `e_index` compare their own node with it by address. A rewrite that replaces the node must move the marker. <details><summary>Notes</summary> Repro (fails on 1.4.3-canary.1+6a92015fc and on main b993710). `git tag --contains f31440d` lists bun-v1.4.1 and bun-v1.4.2, so both releases have the same code: ```sh cat > lib.cjs <<'EOF' exports._helper = function (s) { return "helped:" + s[0]; }; exports.tag = function (s) { return this._helper(s); }; EOF cat > entry.mjs <<'EOF' import * as ns from "./lib.cjs"; console.log(ns["tag"]`z`); EOF bun build entry.mjs --minify-syntax --outfile out/min.js --target bun && bun out/min.js # TypeError: undefined is not an object (evaluating 'this._helper') at $tag ``` `out/min.js` on main holds ``console.log($tag`z`)``. With this change it holds ``console.log(exports_lib.tag`z`)`` and prints `helped:z`. The marker reaches three consumers, all through `IdentifierOpts::is_template_tag` set in `e_dot`: - `maybe_rewrite_property_access` (`src/js_parser/fold.rs:271`) for `import * as ns`. - `record_import_property_use` (`src/js_parser/p.rs:6712`) for a default import. - `note_commonjs_export_use` (`src/js_parser/p.rs:5955`) for `exports.name` in the lifted file itself. Each new test covers one consumer. Each test also has the computed method call (`X["parse"]("y")`), which already worked, so both markers are covered under `minifySyntax`. The name `tag` appears only in computed form in each entry, because one marked use of a name keeps every `X.name` of that file as written and would hide the fault. The second rewrite (`ns["ta" + "g"]`, or an inlined TypeScript enum key) does not go through `maybe_rewrite_property_access` at all. It prints ``exports_lib.tag`z` `` on main and with this change. In esbuild that rewrite happens after `maybeRewritePropertyAccess` and carries no marker. Checked by hand with `--minify-syntax` and `--minify`, all print `helped:z`: `const ns = await import("./lib.cjs")`, `require("./lib.cjs")["tag"]`, `const ns = require("./lib.cjs")`, `import * as ns` through an `export *` barrel, and `import { default as st }`. Sites this change leaves alone: - Other folds check only for a call target, not for a template tag: the comma fold in `e_binary`, the ternary fold in `e_if`, and the `[x][0]` fold in `e_index`. They turn ``(0, o.f)`x` `` into ``o.f`x` ``. That is the opposite fault (the tag gains a receiver). It also reaches plain `bun run`: ``(0, o.f)`x` `` sees `this === o` there, and `undefined` in node. #42452 (section 4) tracks them. - #40829 (open, conflicts with main) is the candidate fix for those folds. Its diff has the same three lines as this change, as one hunk of 26 files. It predates #41251. If this change lands first, #40829 drops that hunk on its rebase. - #42402 (open) changes `has_value_for_this_in_call` at the fold sites. It does not touch this rewrite or `p.template_tag`. The star import test matches the receiver with `\w+` and does not pin `exports_lib`, because #41820 (open) gives `import *` of a lifted module a namespace object of its own, with another name. The default import test and the self test pin the exact output. Suites run on the debug build: `bundler_cjs2esm`, `bundler_minify`, `bundler_cjs`, `bundler_edgecase`, `bundler_dynamic_import_dce`, `esbuild/default`, `esbuild/dce`, `esbuild/importstar`, `esbuild/importstar_ts`, `esbuild/ts`, `transpiler/transpiler`, `transpiler/macro-test`. </details> <!-- robobun:evidence:begin --> --- **[human-review]** gate passed · iteration 0 · 2 files touched <details><summary>fails on main (without fix)</summary> ```console ASAN without fix: BUILD FAILED (no junit output) $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" "test/bundler/bundler_cjs2esm.test.ts" ninja: Entering directory `/workspace/bun/build/debug' [1/66] cc obj/src/jsc/bindings/sqlite/sqlite3.c.o [2/66] gen ZigGeneratedClasses.{cpp,h,rs} Found 2 classes from /workspace/bun/src/jsc/resolve_message.classes.ts - ResolveMessage (15 fields) - BuildMessage (10 fields) Found 1 classes from /workspace/bun/src/runtime/api/Archive.classes.ts - Archive (4 fields, 1 class fields) Found 2 classes from /workspace/bun/src/runtime/api/BunObject.classes.ts - ResourceUsage (8 fields) - Subprocess (20 fields) Found 1 classes from /workspace/bun/src/runtime/api/cron.classes.ts - CronJob (5 fields) Found 3 classes from /workspace/bun/src/runtime/api/filesystem_router.classes.ts - FileSystemRouter (5 fields) - FrameworkFileSystemRouter (2 fields) - MatchedRoute (8 fields) Found 1 classes from /workspace/bun/src/runtime/api/Glob.classes.ts - Glob (5 fields) Found 1 classes from /workspace/bun/src/runtime/api/h2.classes.ts - H2FrameParser (32 fields) Found 9 classes from /workspace/bun/src ... (truncated) release without fix: 3 FAILED bun test v1.4.3-canary.1 (6a92015) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [29.67ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [13.37ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [14.05ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [12.90ms] (pass) bundler > cjs2esm/ExportsFunction [12.86ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [14.55ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [14.10ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [14.87ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [12.71ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [11.37ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [12.24ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [14.95ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvDevelopment [15.54ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRuntimeCondition [11.08ms] (pass) bundler > cjs2esm/UnwrappedModuleRequireAssigned [14.33ms] (pass) bundler > cjs2esm/Unwrap ... (truncated) ``` </details> <details><summary>passes on PR (with fix)</summary> ```console ASAN with fix: all passed $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" "test/bundler/bundler_cjs2esm.test.ts" bun test v1.4.3 (6a92015) test/bundler/bundler_cjs2esm.test.ts: (pass) bundler > cjs2esm/ModuleExportsFunction [956.60ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJSModuleRef [435.19ms] (pass) bundler > cjs2esm/ImportNamedFromExportStarCJS [376.00ms] (pass) bundler > cjs2esm/BadNamedImportNamedReExportedFromCommonJS [410.55ms] (pass) bundler > cjs2esm/ExportsFunction [350.96ms] (pass) bundler > cjs2esm/ModuleExportsFunctionTreeShaking [570.76ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequire [366.45ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPoint [483.54ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPoint [421.50ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireEntryPointImportedByEntryPointSplitting [435.10ms] (pass) bundler > cjs2esm/ModuleExportsEqualsRequireTwoEntryPoints [423.59ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvProduction [613.50ms] (pass) bundler > cjs2esm/ModuleExportsBasedOnNodeEnvDevelopment [603 ... (truncated) release with fix: all passed $ bun scripts/build.ts --profile=release [configured] bun-profile → bun (stripped) in 739ms (unchanged) ninja: Entering directory `/workspace/bun/build/release' [1/61] cc obj/src/jsc/bindings/sqlite/sqlite3.c.o [2/61] gen generated_host_exports.rs generated_host_exports.rs: 122 exports (host=5, lazy=10, generic=107, rust=0); 243 extern-C blocks audited [3/61] gen ZigGeneratedClasses.{cpp,h,rs} Found 2 classes from /workspace/bun/src/jsc/resolve_message.classes.ts - ResolveMessage (15 fields) - BuildMessage (10 fields) Found 1 classes from /workspace/bun/src/runtime/api/Archive.classes.ts - Archive (4 fields, 1 class fields) Found 2 classes from /workspace/bun/src/runtime/api/BunObject.classes.ts - ResourceUsage (8 fields) - Subprocess (20 fields) Found 1 classes from /workspace/bun/src/runtime/api/cron.classes.ts - CronJob (5 fields) Found 3 classes from /workspace/bun/src/runtime/api/filesystem_router.classes.ts - FileSystemRouter (5 fields) - FrameworkFileSystemRouter (2 fields) - MatchedRoute (8 fields) Found 1 classes from /workspace/bun/src/runtime/api/Glob.classes.ts - Glob (5 fields) Found 1 classes from /workspace/bun/src/runtime/api/h2 ... (truncated) ``` </details> <details><summary>diff hotspot</summary> ``` src/js_parser/visit/visit_expr.rs | 3 ++ test/bundler/bundler_cjs2esm.test.ts | 62 ++++++++++++++++++++++++++++++++++++ 2 files changed, 65 insertions(+) ``` </details> **gate history** · 1 passed · 0 rejected · iteration 0 <details><summary>evidence per changed file</summary> ``` file reads edits tests src/js_parser/visit/visit_expr.rs 3 1 12 test/bundler/bundler_cjs2esm.test.ts 3 4 12 ``` </details> <!-- robobun:evidence:end -->
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Problem
exports.x = ...only) that assignsexports.default,import dandimport * as nsin one bundle gaved !== ns.default:ns.defaultwas the liftedexports.default,dwasmodule.exports. Node,bun runand esbuild gived === ns.default. Alsons === d,Object.keys(ns)lackeddefault, and with--splitting(await import(m)).defaultwasexports.defaulttoo once the module assignsexports.__esModule.advance_import_tracker(src/bundler/LinkerContext.rs) bound both the default import andimport *to one object,exports_dep. One object cannot bemodule.exportsand also a namespace whosedefaultismodule.exports.Fix
exports_depstaysmodule.exports. A lifted module also getsvar import_dep = __toESM(exports_dep, 1)in its own part, andimport *binds to it. The part prints after__exportCjs(exports_dep, ...). Tree shaking drops it unless the namespace is used as a value.ns.defaultbinds toexports_dep,ns.xto the lifted$x.d.defaultwith noexports.defaultis nowundefined.exports.__esModuleandexports.default, an importer that is not an ES module by type keeps the CommonJS wrapper for a star import (as for a default import) and unwraps a splitimport()through__toESM(m.default). The chunk itself always exportsmodule.exportsasdefault.test/bundler/bundler_cjs2esm.test.tsgains a 15-cell matrix that compares each bundle withbun runon the same sources (12 cells fail on canary), plus 8 new and 12 updated cases. The Notes list the other suites.bun runmatrix, the user entry point guard documented and pinned by a test, the docs qualified and given a table of whatdefaultmeans per import form).Background
exports.foo = xintovar $foo = xplus an ES module export.exports_depholds a getter and setter per export.{ default: module.exports, ...named }. The default import ismodule.exports.__toESM(mod, 1)(src/runtime.js) returns a new object withdefault: modand a live getter per key, cached permod. esbuild emits it for every CommonJS import.Notes
Output for the report's repro now:
which prints
{"nsDefault":{"default":{"m":"exports.default"},"zz":1},"d":{...same...},"same":true,"keys":["default","zz"]}, the same asnode main.mjsapart from Node's extra"module.exports"key.Where the pieces live:
LinkerGraph.rs: newJSMeta.lifted_namespacecolumn (LiftedNamespace { ref_, part_index }).LinkerContext.rs:create_lifted_namespace_part,lifted_namespace_ref,import_star_was_require_call,split_import_of_lifted_module_needs_to_esm;advance_import_trackerbinds default imports, generatedns.defaultitems and unwrappedrequire()stars toexports_ref;is_esm_namespace_refaccepts the new symbol so member binding and namespace destructuring keep working throughexport * as/export default nsindirections;bind_import_property_accessesresolves.defaulton the new symbol toexports_refand no longer mapsd.defaultto the namespace.scanImportsAndExports.rs: creates the part at the end of step 3 (wrap decisions are final, import matching has not started) and pointsresolved_export_starat it; step 1 extends the__esModulewrapper rule to star imports and makes the splitimport()chunk of a lifted module exportmodule.exportsasdefaultunconditionally; step 6 marks a splitimport()from an importer that is not an ES module by type for__toESM(m.default)when the module sets bothexports.__esModuleandexports.default.generateCodeForFileInChunkJS.rs/findAllImportedPartsInJSOrder.rs: the part prints with the namespace export part and gets no range of its own.Covered shapes (each has a test): plain esm,
--minify,--splitting(the namespace symbol crosses chunks likeexports_depdoes), the lifted module inside a lazy__esmwrapper (the declaration sits next toexports_dep, ahead of the module's dependencies, so a cyclicrequire()back into an importer still sees it),export * as x from/import *; export {}/export default nsindirections,exports.__esModule = trueby assignment from.mjsand.jsimporters (static and split dynamic), and the react-stylemodule.exports = require("./impl")re-export with default import, star import andrequire()in one file.Other suites run:
esbuild/default,esbuild/splitting,bundler_splitting,esbuild/packagejson,esbuild/ts,bundler_edgecase,bundler_npm,bundler_barrel,bundler_minify,bundler_browser,bundler_jsx,bundler_bun,bundler_loader,bundler_string,bundler_plugin,bun-build-api,bundler_cjs,esbuild/importstar,esbuild/importstar_ts,esbuild/dce.Size:
import React from "react"; React.createElement(...)with--productionis byte-identical to main (1443 bytes with react 18.3.1). The extra object and the__toESMhelper appear only when a star import's namespace escapes (Object.keys(ns), passingnsaround). With real react 18.3.1,import * as React+import Rnow prints the same asbun runforR === React.default, React === R, Object.keys(React).length(true false 37).Behavior changes visible to users, all toward Node/esbuild/
bun run:ns !== d(was the same object),Object.keys(ns)starts withdefault.ns.defaultismodule.exports(wasexports.defaultwhen assigned).d.defaultisexports.default, soundefinedwhen not assigned (was the namespace object)..js(not ESM-by-type) file that doesimport * as nsfrom a module withexports.__esModule = true; exports.default = ...(assignment form) now goes through__commonJS+__toESM(…, 0), like a default import from that file already did. Named imports alone still keep such a module lifted.--splitting:(await import("./flag.cjs")).defaultfrom a.mjsimporter ismodule.exports(wasexports.defaultwhen the module assignsexports.__esModule). From a.jsimporter it is stillexports.default, now via__toESM(m.default)at the import site instead of the chunk's export list.Not changed: a lifted CommonJS file used as an entry point itself still exports
defaultas itsexports.default, for its output file and for a splitimport()of it (cjs2esm/SplitDynamicImportOfLiftedCommonJSUserEntryPointpins this; #12463 tracks that shape). TheUserSpecifiedguards inscanImportsAndExports.rsandsplit_import_of_lifted_module_needs_to_esmexist for this reason.The multi-line comments a lint flagged were cut to one line each.
[human-review] gate passed · iteration 0 · 12 files touched
fails on main (without fix)
passes on PR (with fix)
diff hotspot
gate history · 2 passed · 0 rejected · iteration 0
evidence per changed file