Fix YAML front matter not parsed when file ends without trailing newline - #4149

Bug

get_data() in mkdocs/utils/meta.py silently drops YAML front matter when the file ends without a trailing newline after the closing delimiter (--- or ...).

Reproducer

from mkdocs.utils.meta import get_data

# File content with no trailing newline after ---
get_data("---\ntitle: My Page\n---")
# Returns: ('---\ntitle: My Page\n---', {})   ← metadata lost
# Expected: ('', {'title': 'My Page'})

Root Cause

YAML_RE ends with a literal \n:

YAML_RE = re.compile(r'^-{3}[ \t]*\n(.*?\n)(?:\.{3}|-{3})[ \t]*\n', ...)

This requires a newline character after the closing ---/.... When the closing delimiter is the last byte in the file, there is no such newline and the regex does not match. The parser then falls through to the MultiMarkdown path, which also does not recognise --- and returns the entire front-matter block as document content with an empty metadata dict.

Fix

Replace the trailing \n with (?:\n|$) so the pattern matches both a newline and end-of-string. This is backward-compatible: existing files with trailing newlines continue to match as before.

-YAML_RE = re.compile(r'^-{3}[ \t]*\n(.*?\n)(?:\.{3}|-{3})[ \t]*\n', re.UNICODE | re.DOTALL)
+YAML_RE = re.compile(r'^-{3}[ \t]*\n(.*?\n)(?:\.{3}|-{3})[ \t]*(?:\n|$)', re.UNICODE | re.DOTALL)

Verification

pytest mkdocs/tests/utils/utils_tests.py -k meta -v
# 8 passed (6 existing + 2 new)

AI-assisted contribution: this fix was identified and implemented with AI assistance.