[quinnj]

Indexing a ChainedVector with an index vector never checked bounds, so a bad index read arbitrary memory instead of throwing:

julia> x = ChainedVector([[1, 2], [3]]);

julia> x[[1, 4]]
2-element Vector{Int64}:
     1
 38662          # garbage

julia> x[[0]]   # or x[[-1]]
signal 11: Segmentation fault

This happens without @inbounds. The UnitRange method also read before the first chunk for ranges starting below 1, though it then threw a BoundsError from a later checked access.

Both methods now start with @boundscheck checkbounds(x, inds), like the scalar method and Base's own getindex. Under @inbounds the check is skipped as before.

Verification: new tests cover [0], [4], [1, 4], [-1], 0:1, 3:4 and -1:0; full suite passes locally on Julia 1.3.1 and 1.12.6. Gathering 500,000 sorted indices from a 1M-element, 64-chunk vector takes the same time before and after (about 1.6 ms, within noise on a loaded machine). Merges cleanly before or after the other open ChainedVector PRs.

🤖 Generated with Claude Code