fix: honour escape=False for a leading newline in multiline strings

[shivampwm2020]

Problem

tomlkit.string(..., escape=False) can no longer render a multiline string whose value starts with a newline. The value is correct in memory but the serialized document gains a spurious leading newline:

import tomlkit

s = tomlkit.string("\n  aligned\n  strings\n", multiline=True, literal=True, escape=False)
print(repr(tomlkit.dumps(s)))

Clean master:

"\'\'\'\n\n  aligned\n  strings\n\'\'\'"

The extra blank line after the opening \'\'\' means the intended output \'\'\'\n aligned\n strings\n\'\'\' cannot be produced at all - matching the report in #655.

Root cause

tomlkit/items.py, String.from_raw (~line 2314):

if type_.is_multiline() and string_value[:1] in ("\n", "\r"):
    string_value = "\n" + string_value

This re-adds the newline that the parser trims immediately after a multiline opening delimiter, so a leading newline survives a round-trip. It was introduced unconditionally by PR #551 ("fix: preserve leading newline of multiline string built with string()", commit 8cd44f5).

The compensation only makes sense when escape=True. With escape=False the caller explicitly owns the raw body (see tomlkit/api.py:137-153), so prepending a newline corrupts it. Before #551 the escape=False case rendered verbatim.

Fix

Gate the compensation on escape:

if escape and type_.is_multiline() and string_value[:1] in ("\n", "\r"):
    ...

escape=True keeps #551's round-trip preservation (the existing test_create_multiline_string_with_leading_newline_round_trips still passes); escape=False now emits the body exactly as given.

Testing

Regression tests added to tests/test_api.py:

• test_create_multiline_literal_string_with_leading_newline_no_escape
• test_create_multiline_basic_string_with_leading_newline_no_escape

RED (test only, fix reverted):

$ python -m pytest tests/test_api.py -k no_escape -q
assert "\'\'\'\n\n  ali... strings\n\'\'\'" == "\'\'\'\n  align... strings\n\'\'\'"
2 failed

GREEN (with fix):

$ python -m pytest tests/test_api.py -k "no_escape or leading_newline" -q
7 passed

Full suite on the fixed tree: 1204 passed in 6.00s. ruff check tomlkit/items.py tests/test_api.py -> All checks passed!

Fixes #655

[Wkhanex]

With escape=False, multiline basic and literal strings retain the exact supplied raw body, including LF and CRLF at the start. Default escaping still preserves the original parsed value, so the raw-body fix does not remove the protective newline on the ordinary path.

Checked 739d8bc8481d with standalone Python 3.12.14 checks (12 passing assertions). I haven't run the full upstream suite.