Malformed parameter expansion inside a closed legacy-backtick substitution is currently rejected while parsing the outer script, although Bash accepts the script and reports the failure when the child substitution evaluates that word.
Reproduction:
printf 'BEFORE\n'; value=`printf '%s' "${value!}"`; code=$?; printf 'STATUS:%s VALUE:<%s>\n' "$code" "$value"; printf 'AFTER\n'Current behavior: parseShell throws ShellSyntaxError: Unterminated or unsupported parameter expansion; Shell.exec exits 2 and the outer script does not continue.
GNU Bash 5.2.37 accepts the syntax. The malformed expansion fails inside the substitution with status 1, and the outer script continues:
BEFORE
STATUS:1 VALUE:<>
AFTER
The trace-shell compatibility RED reproduced the eager parser failure and outer exit-code mismatch on both MemoryFS and mock S3. The authenticated native fixture is 128 bytes with SHA-256 c01b8b24949870d3f5232ab547b0889f5386a1eea276e98c2e9d6fc52cecc084.
The fix should preserve the malformed expansion as a narrowly scoped runtime failure only within a closed ordinary backtick. Prior child output and effects should remain, later child work should stop, lazy branches/functions/default alternates should remain lazy, and the child status should flow through normal substitution capture. Keep top-level input, $(), process substitution, heredocs, unclosed backticks, array/special/numeric forms, depth limits, and cancellation behavior unchanged. Add paired MemoryFS/mock-S3 regression coverage.
A pending local candidate passes the focused compatibility checks but is not on origin/main or released.
Malformed parameter expansion inside a closed legacy-backtick substitution is currently rejected while parsing the outer script, although Bash accepts the script and reports the failure when the child substitution evaluates that word.
Reproduction:
Current behavior:
parseShellthrowsShellSyntaxError: Unterminated or unsupported parameter expansion;Shell.execexits 2 and the outer script does not continue.GNU Bash 5.2.37 accepts the syntax. The malformed expansion fails inside the substitution with status 1, and the outer script continues:
The trace-shell compatibility RED reproduced the eager parser failure and outer exit-code mismatch on both MemoryFS and mock S3. The authenticated native fixture is 128 bytes with SHA-256
c01b8b24949870d3f5232ab547b0889f5386a1eea276e98c2e9d6fc52cecc084.The fix should preserve the malformed expansion as a narrowly scoped runtime failure only within a closed ordinary backtick. Prior child output and effects should remain, later child work should stop, lazy branches/functions/default alternates should remain lazy, and the child status should flow through normal substitution capture. Keep top-level input,
$(), process substitution, heredocs, unclosed backticks, array/special/numeric forms, depth limits, and cancellation behavior unchanged. Add paired MemoryFS/mock-S3 regression coverage.A pending local candidate passes the focused compatibility checks but is not on
origin/mainor released.