fix(interpreter): loop/return scoping, trap listings, [[ ]] operands and builtin parity from the BashBox corpus - #2629

Requested by Михайло · project thread

What changed

Interpreter-core behavior now matches bash 5.2 in the areas the BashBox corpus covers:

• Loops and return: break/continue never leave a caller's loop and warn outside one; a non-numeric count exits with 128. return with no argument returns $? and ends a sourced file.
• Expansion errors: ${x!} and ${} report "bad substitution", ${1:=x} reports "cannot assign in this way"; both abandon the line.
• Traps: ERR and DEBUG handlers keep $?. trap normalises signal names (0 is EXIT, int/SIGINT), rejects unknown names, and lists in bash order with re-readable quoting. alias and a bare set use the same quoting.
• [[ ]]: -eq/-lt operands are evaluated as arithmetic; an invalid =~ regex returns 2.
• unset: options only before the first name, bad options exit 2, -f with -v is an error, readonly elements are refused.
• Smaller builtins: getopts always writes OPTIND (starts at 1); builtin cat says "not a shell builtin"; hash and source error statuses; pushd/dirs show ~; read -d '' splits on NUL; set -k; a[-5]=x before the start is a bad subscript.

Why

BashBox corpus batch: 47 of the 48 skipped cases in bashbox-interpreter-core.test.sh now pass. The one left needs ENOTDIR for a path under a regular file in the VFS; its skip reason says so.

Before / After

$ trap "echo b" ERR; trap "echo a" EXIT; trap "" INT; trap "it's" SIGTERM; trap
before: ERR first, then EXIT, INT; 'it's' unquotable
after:  trap -- 'echo a' EXIT / trap -- '' SIGINT / trap -- 'it'\''s' SIGTERM / trap -- 'echo b' ERR   (= bash 5.2)

$ trap "echo caught \$?" ERR; false; echo next $?
before: caught 1 / next 0        after: caught 1 / next 1

$ re='('; [[ a =~ $re ]]; echo $?; x='1+1'; [[ $x -eq 2 ]]; echo $?
before: 1 / 1                    after: 2 / 0

Risk

• Medium: control-flow scoping (break/continue/return depth tracking) touches every loop and function call. Merged with fix(builtins): return, unset -v and read reject bad arguments #2613 (return outside a function) and feat(interpreter): deliver signals the shell sends itself #2608 (signal traps); both sets of tests pass. function_recursion_is_bounded_on_a_two_mib_stack still passes.
• type.test.sh and source.test.sh expectations now follow bash, with their bash_diff markers removed.

Checklist

• Tests added or updated
• Backward compatibility considered

Generated by Claude Code