Subshell isolation incomplete: functions, cd, traps, positional params leak

[chaliy]

Description

Subshells ( ... ) should provide full isolation — changes to functions, working directory, traps, and positional parameters should not leak to the parent shell. Currently, several of these leak.

Scope

• Function definitions leak: Functions defined in ( f() {...}; f ) are visible after the subshell
• cd leaks: ( cd /tmp ) changes the parent's working directory (VFS model issue)
• Traps leak: ( trap 'echo child' EXIT ) affects the parent
• Positional params leak: ( set -- x y ) modifies parent's $@

Repro

# Function isolation
( f() { echo inside; }; f )
f 2>/dev/null; echo $?
# bashkit outputs: inside\ninside\n0 (f leaks to parent)
# expected: inside\n127 (f not found in parent)

# Positional params
set -- a b c
( set -- x y; echo "$@" )
echo "$@"
# bashkit outputs: (empty)\n(empty) (params broken)
# expected: x y\na b c

Test coverage

4 skipped tests in crates/bashkit/tests/spec_cases/bash/subshell.test.sh (PR #351).

Oils reference: https://github.com/oilshell/oil/blob/master/spec/subshell.test.sh

Related

• This is expected behavior in bashkit's stateless interpreter model — subshells are not true forks