Variable operators ${@-val}, ${arr[@]+val} on $@ and arrays broken

[chaliy]

Description

The variable test operators (-, +, :-, :+, =, ?) do not work correctly when applied to $@ or array subscripts ${arr[@]}.

Scope

• ${@-minus} — outputs literal ${@-minus} or minus} instead of testing $@
• ${@+plus} — same parsing issue
• ${@:-minus}, ${@:+plus} — same
• ${arr[@]-minus} — broken for empty arrays
• ${arr[@]+plus} — broken for non-empty arrays
• ${var-value} (without colon) — doesn't distinguish unset from empty
• ${var=value} (without colon) — assign-if-unset not working
• Lazy evaluation: ${x:-$((i++))} always evaluates the alternative
• Backslash escapes in default values: ${undef-\$} should produce $

Repro

set --
echo "argv=${@-minus}"
# bashkit outputs: argv=minus} (wrong — trailing brace)
# expected: argv=minus

arr=()
echo ${arr[@]-minus}
# bashkit outputs: -minus} (wrong — literal output)
# expected: minus

echo "${undef-\$}"
# bashkit outputs: (empty) (wrong)
# expected: $

Test coverage

14 skipped tests in crates/bashkit/tests/spec_cases/bash/var-op-test.test.sh (PR #351).

Oils reference: https://github.com/oilshell/oil/blob/master/spec/var-op-test.test.sh

Related

• IFS-based word splitting not implemented #352 (word splitting — $@ handling is interconnected)