Style concern about continued-line strings

[afreiberger]

Operating system: Ubuntu Bionic 18.04
Python version: Python 3.6.8
Black version: 19.3b0-80-g3dc461a (packaged as a snap by Canonical IS team - snap install black-canonical-is --edge)
Does also happen on master: yes

I recently converted some code from 80 character to 120 character line lengths using black and found that a string continuation in the form of:

    print("string with {} vars "
    "issue".format(len(vars)))

will reduce to:
print("string with {} vars " "issue".format(len(vars)))

I expect that the two strings would be concattenated together with the interstitial space taken out such that the resulting line would be:

print("string with {} vars issue".format(len(vars)))

It may be that the current assumption is that the multi-line breaks are tuple/function arg passing with comma separation, rather than also considering the string appending use case I have above.

The resulting code is still valid and executes with replacing the proper variables, but I feel that reducing the close/open quotes around the joined lines would be preferable for style and character reduction on the resulting line.

[zsol]

This is tracked in #26