Do not implicitly expand ~ in pathnames

[Mario Domenech Goulart]

Some procedures available in Chicken implicitly expand ~ to the user home directory if it is the first character in pathnames. They also expand environment variables if pathnames start with $.

The expansions are performed by ##sys#expand-home-path (library.scm).

Florian Zumbiehl submited a ​patch to chicken-hackers proposing the removal of ##sys#expand-home-path. It received some modifications by other contributors. The most recent version of that patch at the time of this writing is ​here.

This change is controversial, since it may break code that rely on the implicit expansion of pathnames. On the other hand, implicit expansion of pathnames may lead to unexpected behaviors or even security vulnerabilities (​examples).

Another source of controversy is that some people consider the implicit expansion of pathnames as a ​convenience and other people consider it ​inconvenient.

Alternatives to minimize or work around the possible breakage caused by the removal of the implicit expansion of pathnames have been proposed along the chicken-hackers thread in question.

It seems that there is a consensus on the removal of the implicit expansion of environment variables in pathnames, so this change request is to eliminate the implicit expansion of ~ in pathnames, which is performed by some procedures provided by the Chicken core.

The discussion period is open and will end on 2013-04-11, when the official poll will be conducted.