#Rust port: e2e parity TODO

Status snapshot (after the current stack lands):

Variant	Score	Failures
Babel	1792 / 1802	10
SWC	1786 / 1802	16
OXC	1704 / 1795	91

The corpus grew by the three ts-* module-interop fixtures (1799 → 1802 on this branch). The Babel/SWC rows are measured on this branch and their failure sets are byte-identical to the pre-stack baseline; the OXC row predates the fixtures and has not been re-measured.

cargo test --workspace: 84 passed, 0 failed.

#SWC

(Historical, pre-ts-interop-stack triage on the old staging base; current snapshot at top.)

The 15 remaining SWC e2e failures fall into three groups. Each line names the fixture and the failure mode; the group it sits in dictates the appropriate fix.

#Group A: Fixture maintenance, not Rust bugs

SWC compiles code that TS rejects, or vice versa, in ways where Rust's behavior is arguably correct. The fix is to rename the fixture (drop the error. prefix) and update the .expect.md snapshot so the suite stops asserting the TS-specific output.

• error.bug-invariant-local-or-context-references.js — TS fires CompilerError::invariant ("expected all references ... consistently local or context"). Rust handles the same code without tripping the invariant.
• error.todo-jsx-intrinsic-tag-matches-local-binding.js — SWC pipeline emits a Todo bailout ([hoisting] EnterSSA: Expected identifier to be defined before being used) that the Babel path does not.
• error.todo-repro-named-function-with-shadowed-local-same-name.js — Babel errors; SWC compiles.
• new-mutability/error.todo-repro-named-function-with-shadowed-local-same-name.js — same as above with the new mutation-aliasing model enabled.
• error.todo-rust-as-expression-assignment-target.tsx — Babel errors; SWC compiles.
• fbt/error.todo-locally-require-fbt.js — Babel emits the Invariant: <fbt> tags should be module-level imports shape; SWC emits Todo: Local variables named 'fbt' may conflict with the fbt plugin. Different categories, both reasonable.

#Group B: External dependency

• use-no-forget-multiple-with-eslint-suppression.js — spurious import { c as _c } in the TS reference output. Fixed on main by react#36500 (merged). Will pass automatically once pr-36173 rebases onto main; until then the TS dist built from pr-36173 still emits the unused import.

#Group C: Real SWC frontend bugs

Each line names the failure mode and a sketch of where to look.

• fbt/fbt-param-with-quotes.js — SWC codegen emits double quotes ("fbt") and reformats multi-line JSX into a single line; Babel uses single quotes and preserves the source layout. Semantically equivalent output; the fix is either an SWC codegen flag for quote style or a post-emit pass. Low impact, high effort.

• lone-surrogate-string-values.js — TS preserves lone surrogates (\uD83E); SWC emits \uFFFD because Wtf8Atom::to_string_lossy() in react_compiler_swc/src/convert_ast.rs::wtf8_to_string replaces invalid UTF-8 sequences. Real WTF-8 handling work that touches every call site using that helper. Probably needs to detect lone surrogates and emit \uXXXX escapes before they hit String.

• many-scopes-no-stack-overflow.js — TS memoizes the function (const $ = _c(401); with 401 memo slots); SWC pipeline bails out and returns the uncompiled source. The fixture exists to test that the compiler handles many sequential reactive scopes without stack overflow, so the SWC variant should compile. Root cause unclear — needs investigation in the SWC pipeline or the compiler core to see where the bail happens.

• pattern4_bare_type.js — Two unrelated bugs in one fixture:

  1. Operator-precedence stripping. Math.round((x - y) * 1000) becomes Math.round(x - y * 1000). SWC codegen drops the parentheses around the subtraction. Probably in convert_ast_reverse.rs's BinaryExpression handling.
  2. Method return type annotation. formatMetrics(): Metrics becomes formatMetrics(). The TS-type-on-binding-ident fix in commit cc1ba1e1 only covered binding identifiers; class method signatures are a separate code path. Same shape of fix; different convert_binding_ident-equivalent call site.

• reduce-reactive-deps/hoist-deps-diff-ssa-instance1.tsx — (x as HasA).a.value + 2 becomes (x as HasA.a.value) + 2. The member expression's property chain gets absorbed into the type annotation when convert_ast_reverse emits the cast. Likely a parenthesization / precedence bug in the reverse converter or the SWC printer's handling of TSAsExpression as the object of a MemberExpression.

• todo-round2_unicode_string.js (prefixed todo-) — Hex escape format (\xC5) vs unicode escape (\u00C5) for bytes 0x80-0xFF. Both valid JS literals; codegen format choice in SWC's string printer.

• todo-round3_promote_used_temps.js (prefixed todo-) — Class body codegen. TS emits the class with fields and constructor; SWC emits an empty class body and pulls fields/methods out into separate assignments. Likely an interaction between SWC codegen and the compiler's promote_used_temps pass.

• ts-non-null-expression-default-value.tsx — Generic type parameter support. const x: ReadonlyMap<string, string> = ... becomes const x = ... (annotation dropped entirely). Our convert_ts_type_to_json helper in cc1ba1e1 explicitly guards against TsTypeRef with type_params to avoid silently emitting ReadonlyMap without the params. The proper fix needs serialization of TSTypeParameterInstantiation in convert_ast.rs AND deserialization in convert_ast_reverse.rs::convert_ts_type_from_json.

#Cross-frontend: TypeScript module interop statements

Three ts-* fixtures pin how TS module-interop statements (import x = require(...), export = x, export as namespace X) must behave: the statement is preserved in output and the file's functions still compile.

• Babel/NAPI and SWC now preserve these end to end. Both flow the statements through Statement::Unknown (the raw Babel-shaped carrier in react_compiler_ast); the SWC frontend rebuilds the swc module declarations in convert_ast_reverse.rs and works around an upstream swc_ecma_codegen bug that prints TsNamespaceExportDecl as export = X (react_compiler_swc/src/ts_namespace_export_fixup.rs, which also carries the guard test that flags when the upstream fix lands). Fixtures renamed from todo-ts-* to ts-*; the SproutTodoFilter entry for the namespace fixture remains (sprout's evaluator cannot evaluate export as namespace).

• OXC remains deferred: todo!() panics in react_compiler_oxc/src/convert_ast.rs (arms TSImportEqualsDeclaration / TSExportAssignment / TSNamespaceExportDeclaration; the sibling TSGlobalDeclaration arm is also unmodeled but unreachable from Babel-parsed fixtures, which represent declare global as TSModuleDeclaration).

• ts-import-equals-declaration.ts

• ts-export-assignment.ts

• ts-namespace-export-declaration.ts

#Babel

(Historical, pre-ts-interop-stack numbers; current snapshot at top.)

TODO: scope this out. Babel is at 1788 / 1795 (7 failures). These have been the baseline throughout the SWC parity stack and were not touched, so the failure list is whatever was on pr-36173 before this work landed.

Next step is to enumerate the failures by fixture and bucket them the same way as SWC (fixture maintenance / external dependency / real bugs). Run:

bash compiler/scripts/test-e2e.sh --no-color --variant babel

…and triage the resulting failures into A/B/C groups under this section.

#OXC

(Historical, pre-ts-interop-stack numbers; current snapshot at top.)

TODO: scope this out. OXC is at 1704 / 1795 (91 failures). The CLI filename fix in commit c30f0d6f bumped this by +2 from the 1702 baseline, but everything else is unaddressed.

Next step is to enumerate failures and identify OXC-specific clusters (likely AST conversion gaps in react_compiler_oxc analogous to the SWC work in this stack). Run:

bash compiler/scripts/test-e2e.sh --no-color --variant oxc

…and bucket the resulting failures into A/B/C groups under this section. Expect significant overlap with the SWC Group C bugs (cast wrappers, type annotations, UTF-16/WTF-8 handling) since both frontends share the post-conversion pipeline.

#How this stack got here

(Historical, pre-ts-interop-stack numbers; current snapshot at top.)

• compiler/scripts/test-e2e.sh --variant swc baseline was 1742 / 1795 (53 failures) before this stack.
• 9 commits in the current stack reduce that to 1780 / 1795 (15 failures, -38 fixtures, 72% reduction).
• Babel variant: 1788 / 1795 throughout (no regressions).
• OXC variant: 1702 → 1704 (the CLI filename commit also benefited OXC).
• cargo test --workspace: 56 passed, 0 failed throughout.