fix(2.x): quote path variables in write_source_file

[jfjonsson]

Summary

Backport of #1239 to 2.x. Fix write_source_file failing with shell syntax errors when paths contain metacharacters like parentheses.

Problem

The generated shell script assigned paths to variables without quoting:

in=$runfiles_dir/path/to/(folder)/file.txt
out=path/to/(folder)/file.txt

Bash interprets ( as the start of a subshell, causing:

syntax error near unexpected token `('

This breaks builds using Next.js App Router route groups (e.g., app/(dashboard)/page.tsx) or any path with parentheses, spaces, or other shell metacharacters.

Fix

Quote the variable assignments:

in="$runfiles_dir/path/to/(folder)/file.txt"
out="path/to/(folder)/file.txt"

Changes

• lib/private/write_source_file.bzl: Quote path variable assignments in both bash and batch scripts
• lib/tests/write_source_files/write_source_file_test.bzl: Quote paths in test script generator
• Added regression test with parentheses in path ((route-group)/test.js)

Test plan

• New test special_chars_in_path_test passes
• All existing write_source_files tests pass