Bug

Repeat#lastIndexOf returns this.size when the searched value matches, but the last valid index of a Repeat of n elements is n - 1.

const { Repeat, List, Seq } = require('immutable');

Repeat('x', 3).lastIndexOf('x');        // => 3  (should be 2)
List(['x','x','x']).lastIndexOf('x');   // => 2  ✅
Seq.Indexed(['x','x','x']).lastIndexOf('x'); // => 2  ✅
['x','x','x'].lastIndexOf('x');         // => 2  ✅ (native)

Every other indexed collection (List, Range, generic Seq) and the native Array return size - 1; only Repeat was off by one.

While fixing this I noticed a related issue on empty repeats — both indexOf and lastIndexOf reported the value as present even though the collection has no elements:

Repeat('x', 0).indexOf('x');      // => 0  (should be -1)
Repeat('x', 0).lastIndexOf('x');  // => 0  (should be -1)

lastIndexOf('missing') is documented to return -1 when the value isn't found, and an empty collection contains nothing, so both should return -1.

Fix

In src/Repeat.js:

• lastIndexOf returns this.size - 1 (instead of this.size) on a match.
• both indexOf and lastIndexOf guard on this.size !== 0 so an empty Repeat returns -1.

The infinite case is unchanged: Repeat(value) has size === Infinity, so size - 1 is still Infinity.

Tests

Added regression tests to __tests__/Repeat.ts covering the first/last index of a non-empty repeat and the empty-repeat case. They fail on main (lastIndexOf returns 3 instead of 2; empty repeat returns 0 instead of -1) and pass with the fix. Full suite (798 tests) green, eslint + prettier clean.