Index 0 of an empty array returns parse-error status instead of missing-index status

[memotype]

Severity: Medium
Expected real-world likelihood: Medium to high

Problem

Querying index 0 of an empty array returns status 2, while other out-of-range indexes return the documented missing-index status 1.

Empty lists are common in API and provisioning data. Iteration still stops because both statuses are nonzero, but callers that distinguish missing data from malformed/unsupported input receive the wrong result.

Reproduction

./bj.sh '[]' 0
printf 'status=%s\n' "$?"

./bj.sh '[]' 1
printf 'status=%s\n' "$?"

Actual:

index 0: status=2
index 1: status=1

Nested form:

./bj.sh '{"items":[]}' items 0
# Actual: empty output, status 2
# Expected: empty output, status 1

Suspected cause

Index 0 uses a shortcut:

[) [[ $q = 0 ]] || co 1 ;;

For an empty array, this bypasses container scanning. The following final-output iteration then encounters ] as an unexpected token and returns status 2.

Possible fixes (suggestions only)

These are possible approaches, not prescribed implementations:

• Have the index-zero path detect an immediate closing bracket and return missing-index status 1.
• Route index zero through list scanning while preserving the fast path for nonempty arrays.
• Refactor list selection so every index, including zero, shares one exhaustion-status path.

Suggested regression coverage

Against the readable source and generated forms:

• root and nested empty arrays queried at index 0;
• indexes 1 and larger on empty arrays;
• index 0 on single-element arrays;
• iteration over an empty array terminates immediately with exact status 1;
• whitespace inside the empty array, such as [ ].