scriptc/tests/corpus/union-nested-layout-discriminant.ts

// Mapping a recursive variant before the whole union preserves separate
// layout ids for bin and logical. Later inferred literals can share either.
type Expr =
  | { kind: "number"; value: number }
  | { kind: "bin"; op: "+" | "==="; left: Expr; right: Expr }
  | { kind: "logical"; op: "&&" | "||"; left: Expr; right: Expr }
  | { kind: "nullish"; left: Expr; right: Expr }
  | { kind: "ternary"; cond: Expr; then: Expr; else_: Expr };

function binary(value: Expr & { kind: "bin" }): Expr { return value; }

function inferred(left: Expr, right: Expr): Expr {
  const value = { kind: "bin" as const, op: "+" as const, left, right };
  return value;
}

function callback(left: Expr, right: Expr): () => Expr {
  return () => ({ kind: "bin" as const, op: "+" as const, left, right });
}

function build(left: Expr, right: Expr, conditional: boolean): Expr {
  const missing = conditional ? {
    kind: "ternary" as const,
    cond: { kind: "bin" as const, op: "===" as const, left, right },
    then: left,
    else_: right,
  } : left;
  return missing;
}

function inspect(root: Expr): void {
  const pending = [root];
  while (pending.length !== 0) {
    const e = pending.pop()!;
    if (e.kind === "logical" || e.kind === "nullish") {
      console.log(e.kind);
      pending.push(e.right, e.left);
    } else if (e.kind === "ternary") {
      pending.push(e.else_, e.then, e.cond);
    } else {
      console.log(e.kind);
    }
  }
}
const left: Expr = { kind: "number", value: 1 };
const right: Expr = { kind: "number", value: 2 };
console.log(binary({ kind: "bin", op: "+", left, right }).kind);
inspect(build(left, right, true));
inspect(build(left, right, false));
inspect(inferred(left, right));
inspect(callback(left, right)());
inspect({ kind: "logical", op: "&&", left, right });
inspect({ kind: "nullish", left, right });

// Native compilation of array search synthesizes a branching expression
// with a nested binary comparison, exercising this conversion in the compiler.
function packageSegment(path: string): number {
  return path.split("/").lastIndexOf("node_modules");
}
console.log(packageSegment("/workspace/node_modules/package"));
console.log(packageSegment("/workspace/src"));