[cramforce]

The typescript-go panic behind s.match(re) ?? []

In s.match(re) ?? [] (and || []), the empty literal is contextually typed by the tuple-like match result. typescript-go clones an empty tuple as an array literal, and the clone keeps the tuple flag without tuple data. The API then panics whenever it serializes the union's members (interface conversion: checker.TypeData is *checker.TypeReference, not *checker.TupleType, in internal/api/proto.go). An earlier fix kept the panic from failing the whole program, but every statement that needed the members still reported SC0004.

When getTypesOfType panics, the constituent read now asks for the union's widened type instead. Its members are readable and describe the same values, so they become the union's members. If widening does not help, the existing behavior stays. The empty tuple beside a RegExpMatchArray/RegExpExecArray is one of the match array's own values, as it already was beside a plain array. With both changes, const matches = text.match(re) ?? [] is a plain match array, and checker-panic-tuple.ts now compiles and moves to the corpus.

Smaller gaps

• Tuple spreads: [...TUPLE, ...rest], where TUPLE: [string, string, string, string, string], copies the tuple's positions into the literal's element type.
• fs.Stats arrays: fs.Stats is now an array element kind. Stats are refcounted handles, so arrays use their retain/release adapters and need no tracing. await Promise.all(files.map((f) => stat(f))) and stats.reduce(...) compile.
• Primitive constructors as then handlers: .then(String), .then(Number) and .then(Boolean) over a number or boolean settled value convert it through an interned closure. A string settled value already fit the constructors' value form and keeps its old path.
• Error subclasses with fields: util.format(err), %s and util.inspect of an Error-typed value were refused when any error subclass in the program declares fields. Now, for each fielded subclass (most-derived first), an instanceof arm prints the stackless error base, then the own properties, using the same single-line/multi-line rule as any object, counting the base: [Bailable [Error]: m] { bail: true }.
  • The header applies Node's constructor-name rule (Bailable [Error] vs FetchFailedError).
  • Beyond the depth budget, an instance prints [Name].
  • A subclass whose own fields cannot render (functions, or a field that Node's error inspector treats specially) throws a named refusal on its own instances only.
  • This is stacked on Inspect program-declared Error subclasses with Node's constructor-name header #1520, which renders field-less subclasses with the same header. Field-less classes in a hierarchy that also has fielded subclasses get header-only arms here, so class Plain extends Error {} prints [Plain [Error]: m] and not [Error: m]. 6525 covers this.

Evidence

• New corpus programs, each refused on main and matching Node byte for byte in the plain and sanitized lanes:
  • 6520 match-or-empty-widened
  • 6521 tuple-spread-into-array
  • 6522 stats-arrays
  • 6523 then-primitive-constructors
  • 6525 error-subclass-fields
  • 6524 match-or-empty-tuple (the former checker-panic-tuple.ts)
• Zero-cost gate against origin/main e1c2717: PASS. 2550 programs are identical. 4642-acyclic-contract.ts fails on both sides, as it already does on main. Self-hosted compile time -0.01%. The bench timing interval came out inconclusive, but every program is byte-identical, so the difference is noise.
• After the rebase onto Inspect program-declared Error subclasses with Node's constructor-name header #1520 (256b7cd), the zero-cost gate against that base also passes: 2550 programs are identical, plus the same both-fail. 6520 to 6525 and 6530 pass in both lanes.
• pnpm lint and pnpm format:check are clean. pnpm test:ts7 --baselines-only passes, with the new baselines recorded and the moved fixture's baseline moved. diagnostics.test.ts: 203/203.
• The self-hosted compiler's IR build reports no diagnostics, and tests/harness/self-hosting-native-driver.test.ts passes.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
scriptc	Ready	Preview, v0	Oct 20, 2026 4:37pm UTC