Strings should remain on separate lines if they end with “\n”

[15r10nk]

Describe the style change

Strings should remain on separate lines if they end with “\n”. The newline has already the meaning of a line-break in a string. I think it would improve the readability if black uses this information to format strings.

Examples in the current Black style

a = "a=1\n" "b=2\n" "c=3\n"

Desired style

a = (
    "a=1\n"
    "b=2\n"
    "c=3\n"
)

Additional context

I'm the author of inline-snapshot and I use currently multi-line strings to generate strings with newlines, but it is not possible for black to indent theses strings.

from inline_snapshot import snapshot


def gen_code():
    return "\n".join(f"{name}={num}" for num, name in enumerate(("a", "b", "c")))


def test():
    assert gen_code() == snapshot(
        """\
a=0
b=1
c=2\
"""
    )

I would like to generate code like the following, but black merges the strings, which makes them hard to read.

from inline_snapshot import snapshot


def gen_code():
    return "\n".join(f"{name}={num}" for num, name in enumerate(("a", "b", "c")))


def test():
    assert gen_code() == snapshot(
        "a=0\n"
        "b=1\n"
        "c=2"
    )

> black

from inline_snapshot import snapshot


def gen_code():
    return "\n".join(f"{name}={num}" for num, name in enumerate(("a", "b", "c")))


def test():
    assert gen_code() == snapshot("a=0\n" "b=1\n" "c=2")

It would be nice if the strings can stay on separate lines if they end with newlines, or to have another way to generate multi-line strings which can be indented.