Re: Strange `file-name-sans-extension' behavior

[Richard Stallman]

    > The directory it uses is the one that was in the argument file name.
    > If it was valid there, it should be equally valid in the result.
    > If it is not valid in the result, I guess it was not valid in
    > the argument.

    The problem is the slash you append to the directory if it doesn't
    end in a slash.

I don't see any code in file-name-sans-extension to append a slash to
the directory name.  It gets the directory name with
file-name-directory and uses it without further change.

Where is the slash appended?