[cramforce]

Two shapes that keep common npm packages and service code from compiling.

JSON tables whose rows mix strings and numbers

// a character-set table: [["8140", 12288, 65292], ...]
const table = require("./table.json");
// a code-point range map: [[[0, 44], "disallowed"], [[65, 65], "mapped", [97]], ...]
const ranges = require("./ranges.json");

JSON documents a CommonJS package requires, and JSON modules a TypeScript file imports, bake into the binary as literals. The baker accepted numbers, strings, booleans, arrays and records, but not unions, so rows typed (string | number)[] or (string | number[])[] were refused, with a misleading "elements have no array representation" message. iconv-lite's encoding tables and tr46's mapping table have exactly this shape.

Literals now bake union-typed elements: each JSON value takes the first arm of the union it fits, by its JSON kind and, for arrays and records, its contents (records are exact, as before). null values and null-valued fields bake as null.

Array destructuring of unions of arrays and tuples

const [match, head, word] = /(\w*)-(\w+)/.exec(text) || ["", "", ""];
function pick(flag: boolean): [string, number] | string[] { ... }
const [p, q = 0] = pick(true);

re.exec(s) || ["", "", ""] has the type RegExpExecArray | [string, string, string], a union of an array and a tuple, which array destructuring refused (only unions of arrays compiled). Each position now reads the arm the value holds: a tuple arm answers its field, or undefined past its end; an array arm its element, or undefined past its end. A string arm (re.exec(s) || "") answers its code point at the position, as the string iterator does. Defaults fire exactly where JavaScript's do. Rest elements over such unions stay refused.

Tuple unions and discriminants

A union of tuple types ([string, boolean] | [string, boolean, number]) picked the checker's length literal as its discriminant, but tuple shapes keep only their positions, so the validator rejected the union with an internal error once a program materialized it (which the destructuring above now does). Tuple unions no longer get a discriminant.

Evidence

• Corpus: 6410-json-mixed-scalar-tables (two packages modeled on a character-set table and a code-point range map, required at load and inside a function, plus an ES module JSON import) and 6411-union-array-tuple-destructuring.ts. Both match Node byte for byte in the plain and sanitized lanes.
• Diagnostics: the json-shape fixture's document compiled once its null field baked, so it now uses a value no literal can spell (1e400, which parses to Infinity) and still reports at the import. diagnostics.test.ts: 199/199.
• Zero-cost gate against main bf2afee on the compiler tip: PASS, with all 2501 bench, self and corpus programs identical (IR, LLVM and release executables). The bench geomean changes by -0.06% and self-compile time by +0.01%, both within tolerance. An earlier run on the first commit also passed. The self-hosted compiler IR build exits 0 with no diagnostics.
• pnpm lint and pnpm format:check are clean, and pnpm test:ts7 --baselines-only passes, with 2 new baselines and no existing ones changed.
• No compatibility rows change.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
scriptc	Ready	Preview, v0	Oct 20, 2026 4:40pm UTC