v0.5.1

What's Changed

Fixes

• Metadata lines split only at real line endings: fmf_write and
  fmf_insert_frontmatter split the YAML text with str.splitlines(), which also breaks
  at LS, PS, NEL, VT, FF and the FS, GS and RS separators. A value holding one of them got
  a real line break in the file and read back changed, with no error. The writers now
  split only at LF, CRLF and CR, the line endings the readers recognize.
• Strings with line-break and control characters read back exactly: ruamel wrote NEL,
  LS, PS and CR raw outside double quotes, where a reader takes them as line breaks: a NEL
  read back as a space, and a CRLF in a multi-line string came back as LF. A multi-line
  string holding a NEL or a character outside YAML 1.2’s c-printable set (the C0 and C1
  controls but tab, LF, CR and NEL; DEL; U+FFFE and U+FFFF) was written as YAML that did
  not parse. Such strings are now written double-quoted with escapes (see below).
• A # preamble is kept: fmf_insert_frontmatter and fmf_strip_frontmatter
  dropped a shebang or PEP 723 block that came before hash-style frontmatter. Both now
  keep those lines.
• Atomic writes keep the file mode: fmf_write, fmf_insert_frontmatter,
  fmf_strip_frontmatter and write_yaml_file used one fixed temp name per target, so
  concurrent writes to one file could collide and fail, and they reset a replaced file’s
  mode, so a 0755 script came back as 0644. Every write now goes through its own
  exclusively created temp file beside the target, removed on any error, and keeps the
  replaced file’s mode. On a filesystem that refuses chmod, such as some FUSE mounts, the
  write still happens with the default mode, as does a new file (0o666 less the umask).
• The C-first gate admits only ruamel.yaml.clib: The gate checked the libyaml
  version string, which ruamel.yaml.clibz also reports, though it is a different build
  (compiled with Zig, with a free-threading flag) that the search behind the guards never
  covered. No ruamel release hands clibz’s parser to YAML() yet, but one that did would
  have put the readers on it. They now use libyaml only through clib’s own parser and
  read pure otherwise. Results are unchanged; only speed is affected.
• ruamel.yaml 0.19.0 is excluded: It was the one release that depended on clibz by
  default, which builds from source with Zig at install time. The dependency is now
  ruamel-yaml>=0.18.10,!=0.19.0.

Behavior Changes

• Escaped output for those strings: A string holding NEL, LS, PS, CR or any
  character outside c-printable is now always written double-quoted, as \N, \L,
  \P, \r, \0, \x1F and so on, whatever style was asked for. This applies to keys
  and values in every writer and every new_yaml instance. For the control characters
  it changes only output that could not be read back. Every other string’s output bytes
  are unchanged.
• Blank, comment-only and null frontmatter read as None: ---\n\n---,
  ---\n# note\n--- and ---\n~\n--- (or null) raised FmFormatError, while empty
  frontmatter (---\n---) returned None metadata. All of them now return None. Any
  other value that is not a mapping still raises.
• fmf_has_frontmatter returns False for an unclosed delimiter: A file that starts
  with a Markdown --- thematic break and has no closing delimiter made it raise. It now
  returns False. fmf_read still raises on such a file.
• Inserting a non-hash style after # lines raises: On a file that begins with a
  shebang or PEP 723 block, fmf_insert_frontmatter with any style but hash now raises
  FmFormatError and leaves the file unchanged, since only hash-style frontmatter can
  follow those lines. Before, it dropped them.

Performance

• Cheaper routing checks: The check that decides whether a text may go to libyaml
  settles typical frontmatter from character counts, in about 1 µs instead of 27 µs. It
  routes every text as before.
• fmf_read_raw opens the file once: It reads the body from the same stream as the
  frontmatter instead of opening the file again.

Full commit history: v0.5.0...v0.5.1