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.

[felix winkelmann]

Attached is a patch that provides ep, a procedure performing explicit tilde-expansion in pathnames, a suggestion by sjamaan.

[sjamaan]

This patch is very complete! Thanks, Felix.

[felix winkelmann]

Uh, not complete enough. This one adds types.db and import-lib entries.

[Mario Domenech Goulart]

Poll(Should ~ be implicitly expanded in pathnames?; Yes; No)?

[felix winkelmann]

Replying to mario:

Poll(Should ~ be implicitly expanded in pathnames?; Yes; No)?

[Mario Domenech Goulart]

This poll has been closed. Since all voters opted for "no", CHICKEN procedures won't implicitly expand ~ in pathnames.

Now, back to polishing patches to implement that.

[felix winkelmann]

Note that the current behaviour can only be deprecated or too much old code would break.

[Mario Domenech Goulart]

Felix's patch modified to be cleanly applied to master as of 2013-07-09

[Mario Domenech Goulart]

We have decided to remove the implicit expansions from the core and implement the expansions in an egg. See ​http://lists.gnu.org/archive/html/chicken-hackers/2013-11/msg00077.html for the discussion and decisions.

The current situation at the time of this writing is: 4.9.0 will deprecate implicit expansions and 4.10.0 will remove them.