Highlights

This release is a milestone: it fixes Black's first CVE security vulnerability. If you
run Black on untrusted input, or if you habitually put thousands of leading tab
characters in your docstrings, you are strongly encouraged to upgrade immediately to fix
CVE-2024-21503.

This release also fixes a bug in Black's AST safety check that allowed Black to make
incorrect changes to certain f-strings that are valid in Python 3.12 and higher.

Stable style

• Don't move comments along with delimiters, which could cause crashes (#4248)
• Strengthen AST safety check to catch more unsafe changes to strings. Previous versions
  of Black would incorrectly format the contents of certain unusual f-strings containing
  nested strings with the same quote type. Now, Black will crash on such strings until
  support for the new f-string syntax is implemented. (#4270)
• Fix a bug where line-ranges exceeding the last code line would not work as expected
  (#4273)

Performance

• Fix catastrophic performance on docstrings that contain large numbers of leading tab
  characters. This fixes
  CVE-2024-21503.
  (#4278)

Documentation

• Note what happens when --check is used with --quiet (#4236)