perry-codegen: String.slice() 0-arg form unsupported #316

What happened

Perry's codegen rejects the standard String.prototype.slice() 0-arg form (a common idiom for "clone this string") with:

perry-codegen: String.slice expects 1 or 2 args, got 0

Surfaced compiling effect/src/internal/redBlackTree/iterator.ts::RedBlackTreeIterator::clone during the #309 compat sweep.

What you expected

MDN spec for String.prototype.slice: all of slice(), slice(start), and slice(start, end) are valid. The 0-arg form returns the whole string.

Minimal reproduction

const s = "hello";
const copy = s.slice();
console.log(copy);   // expected: "hello"

perry compile repro.ts -o /tmp/out
# fails with: perry-codegen: String.slice expects 1 or 2 args, got 0

Likely fix site

crates/perry-codegen/src/lower_string_method.rs — search for the slice arm. Treat 0 args as slice(0, length) (i.e. clone). Same fix shape that Array.prototype.slice() (without args) already supports.

Environment

• Perry version: 0.5.405
• Host OS: macOS 26.4 (arm64)
• Target: native
• Effect version: 3.21.2 (where this surfaced)

Discovered as part of the #309 long tail.