fix(hir): export default F exports the declared function's own binding - #10548
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`function F(){}; export default F;` lowered to a synthetic `default`
export row, so importers materialized a second function object: no
prototype methods or statics assigned on F, `F === imported` false, and
missing arguments unpadded when called through a value. Export the
binding itself, as `export { F as default }` does, and mark a function
named by an export row as exported after the whole module is lowered so
an export clause ahead of its hoisted declaration resolves the same way.
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: defaults Review profile: CHILL Plan: Advanced Run ID: 📒 Files selected for processing (1)
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Included review availability: Your plan provides up to 8 included reviews per hour; 3 remain after this review. 📝 WalkthroughWalkthroughThe lowering pipeline preserves the declared function object for ChangesDefault function export identity
Priority: ⬆️ High Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix · Severity of issue fixed: Medium Sequence Diagram(s)sequenceDiagram
participant ModuleLowering
participant FunctionBinding
participant ExportTable
participant Importer
ModuleLowering->>FunctionBinding: resolve export default F
FunctionBinding->>ExportTable: record local F as exported default
ModuleLowering->>FunctionBinding: mark hoisted exported body
Importer->>ExportTable: read default binding
ExportTable-->>Importer: return the existing function object
Merge Risk: ⚪ Minimal · up to The default-export lowering change has no identified merge-blocking risk in the available evidence. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 55.17% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 18 files. (1 skipped: 1 unsupported.)
✨ Finishing Touches🧪 Generate unit tests (beta)
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Inline comments:
In `@changelog.d/10548-export-default-fn-identity.md`:
- Around line 24-27: Update the changelog sentence near the hoisted-export
examples to clarify that the alias form loses identity only when its export
clause precedes the hoisted declaration, because the function body was not
marked as exported; preserve the earlier statement that alias exports otherwise
already work.
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changelog.d/10548-export-default-fn-identity.md
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Follow-up on the review comment and CI. Changelog wording (CodeRabbit, CI on 3b535d2: green except
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Landed via merge train #10578 (v0.5.1593). All source commits preserve authorship; merged main matches the validated train exactly. |
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Summary
function F(){}; F.prototype.m = …; export default F;(andfunction f(){}; export default f;in general) gave importers a different function object from the module's ownF:Fwere missing in the importer (new F().mwas undefined,F.tagwas undefined),F === importedFwas false,const g = f; g(),.call,.apply,new) passed garbage for missing arguments and skipped default and rest parameter handling.This blocked axios 1.19.0 (
AxiosURLSearchParams.prototype.append), uuid 14.0.1 (v5.DNS) and lodash-es 4.18.1 (MapCache.prototype.clear). With this changeexport default FexportsFitself.Root cause
crates/perry-hir/src/lower/module_decl.rs:1876(theExportDefaultExprarm): whenexport default <expr>lowered toExpr::FuncRef, the export row wasExport::Named { local: "default", exported: "default" }.The CLI driver maps a renamed declared-function export back to its local name only when the row names that local and the function is
is_exported(crates/perry/src/commands/compile/run_pipeline.rs:1832-1840). Withlocal: "default"that mapping never happened. Importers therefore took the__perry_wrap_perry_fn_<src>__defaultclosure wrapper, which is emitted by the #967 branch incrates/perry-codegen/src/codegen/artifacts.rs:1129. That wrapper forwards calls toF's body, but it is a separate closure singleton:F's expandos orprototype,js_register_closure_arityregistration, which is where the garbage arguments came from.export { F as default }already wrote{ local: "F", exported: "default" }and worked.A second, smaller defect had the same symptoms.
is_exportedis flipped by the export arms only on functions already lowered. An export clause that comes before its hoisted declaration (export { F as default }; function F(){}orexport default F; function F(){}) left the flag unset, so the alias form lost identity the same way.Fix
In the new file
crates/perry-hir/src/lower/module_decl/default_export_binding.rs(the parentmodule_decl.rsis at 1,944 lines, so the logic can't go there):default_export_function_binding: when the exported expression is an identifier naming that function, looking through parentheses and erased TypeScript wrappers (as,!,satisfies,<T>,as const, instantiation), the row becomes{ local: "F", exported: "default" }. That is exactly theexport { F as default }shape. OtherFuncRefexpressions, such as a function expression, have no local binding and keep the old row.mark_exported_function_bodies: runs once after the whole module is lowered. It marks a function exported when anExport::Namedrow names it as its local binding andexported_functionslists its id. A value alias (export const g = F) namesg, so it does not markF. A unit test pins that.Diff: +11/−1 in
module_decl.rs, +1 inlower_module_fn.rs, plus the new file, most of which is unit tests.Tests
test-files/test_gap_10434_export_default_fn_identity.ts, with helpers intest-files/_helpers/export_default_fn_10434/. It covers:instanceofboth ways; a static factory,.call/.apply, a loop over two function values,export default Fand theexport { F as default }forms, andexport default (F as unknown as typeof F),export { F as default },export default function F(){}, a class, an arrow in a const and a function expression in a const.TypeError: describe is not a functionon the fourth line. With each line guarded, every target line differs from Node and every control matches. On this branch the output is byte-identical to Node. Harness runs:--filter test_gap_10434gives PARITY_FAIL on the baseline binary and PASS on this branch.default_export_binding.rs): the export row andis_exportedforexport default F, for export-before-declaration in both forms, and through parentheses and type assertions; plus the value-alias non-change. With both helpers stubbed to their pre-fix behaviour, the four fix tests fail (4/4).Validation
cargo test --release -p perry-hir --testscargo test --release -p perry --testsexport defaultorexport {}. I reran the 15 integration failures in the same tree at this branch and at 7661bc0 (same-pbuild set): the same 15 fail on both, and the baseline fails one more (allow_eval_env_overrides_strict_config). The remaining one,geisterhand::warm_archives_are_rebuilt_as_one_runtime_graph(Failed to run cargo … No such file or directory), is a host-environment failure and was not rerun../scripts/run_lint_gates.sh(full, compile tier included)Public benchmark evidence freshness(benchmarks/ci_public_baseline_check.py), same failure on a 7661bc0 checkoutPERRY_SKIP_BUILD=1 ./scripts/run_gap_tests.sh)GAP_EXIT=0(snapshot OK). The 6 non-passing tests are the same 6 as the baseline run on 7661bc0. The only status differences: the newtest_gap_10434_export_default_fn_identitypasses, andtest_gap_9536_fetch_url_errorwasnode_failin the baseline run (Node-side) and passes here. No new failures.python3 scripts/check_test_registration.pyPerformance
perf stat -e instructions, Linux x64, 3 runs each,PERRY_NO_AUTO_OPTIMIZE=1, same commit for both arms. Node 26.5.1 wall time is for context only; the host was at load 100–300.step(acc, i)to a default-importedfunction stepexport { step as default }(control)fns[0](acc, i))export { step as default }(control)new V(i, 2)+a.dot(new V(3, i)), default-imported constructor functiondot is not a function)export { Vec as default }(control)benchmarks/bench_fibonacci.ts(unrelated control)The default export now behaves exactly like the existing
export { F as default }path on every row. The +0.68% on the through-a-value row is not new work. The importer IR is byte-identical apart from the wrapper symbol, and the producer IR is identical. The new target,__perry_wrap_…__step, is the closure that carriesjs_register_closure_arity, so the runtime's closure call does its normal arity-aware dispatch. The baseline's unregistered__defaultwrapper skipped that dispatch, and that is why it passed garbage for missing arguments.Pre-existing and not changed here: on these rows Perry is well behind Node, and the alias controls show the gap is identical before and after. Task-clock was about 2.0 s against Node's 0.56 s for the 100M direct default-import calls, and about 1.0 s against 0.23 s through a value. This change neither adds to that gap nor closes it. Part of it: a default-imported function in a hot loop costs about 4.5× the instructions of the same function imported by name (16.5B vs 3.7B above).
localize_cross_module_functions(crates/perry-transform/src/inline/cross_module.rs:562-583) only localizesImportSpecifier::Named, so default imports are never cross-module inlined. This is a follow-up, see below.Package check (informational)
import axios from "axios"withcompilePackages: ["axios"]):TypeError: append is not a function.new AxiosURLSearchParams(...)hasappend/toString, andbuildURL,getUri, a GET with params and a JSON POST against a local Node server all match Node.response.headers["x-custom"]reads undefined,err instanceof AxiosErroris false for a 404,timeout: 50never fires,URLSearchParamsrequest body is JSON-serialized as{"_entries":[…]}becauseObject.prototype.toString.call(new URLSearchParams())is[object Object].v5.DNSundefined andTypeError: Namespace must be array-like; this branch matches Node (v5.DNS,v3.URL,v5(),v3(), andv1/v4/v7called through values).TypeError: clear is not a function; this branch matches Node forget,memoizeandset.import Long from "long"probe (fromInt,fromString,multiply) already matched Node on the baseline. The mysql2packet.jspath from the issue was not re-run.Not verified
longpath the issue names).Follow-ups noticed (not fixed here)
gather_cross_module_functionscopies a small exported function together with the helpers it references byFuncRef, including value-position references. Sofunction f(){}; export function isSame(x){ return x === f; }; export { f };returnsfalseforisSame(importedF): the inlinedisSamecompares against the importer's private clone off. Expandos read inside a cloned body read the clone too. The bug is independent of this PR and also affects plain named exports.newon anany-typed function constructor is slow: ~17k instructions pernew V(i, 2)and ~5.5k pera.dot(b)prototype call, on the baseline as well, same module.Fixes #10434
Summary by CodeRabbit
Bug Fixes
instanceofchecks, and default or rest parameters.Tests