Heredoc Fix is a parser regression fix for Claude Code 2.1.10 that eliminates crashes when bash heredocs contain JavaScript template literal syntax.

What Was Fixed

The runtime crashed when parsing bash commands containing heredocs with template literal expressions like ${index + 1} or ${a + b + c}. The parser incorrectly interpreted these as shell variable interpolations instead of literal string content, causing execution to fail.

How the Test Worked

The test executed two concrete heredoc patterns in Claude Code:

cat << 'EOF'
const result = items.map((item, index) => ${index + 1});
EOF

cat << 'EOF'
let sum = ${a + b + c};
EOF

Both commands ran without crashing. The single-quoted 'EOF' delimiter correctly prevented shell interpolation, and the fix allowed the parser to handle the template literal syntax properly.

What It Solves

This addresses a regression, not a new feature. It restores the expected behavior where heredoc delimiters suppress shell variable expansion and preserve literal text. The fix maintains the semantic boundary: content between quoted delimiters is treated as a string, not as a parsing context for interpolation logic.

Verification

Tested 2026-01-16 via echo 'heredoc command' | claude -p with no crashes observed across both test cases. Status: PASS.