[MacPorts] #18602: Prevent MacPorts from being configured with --prefix=/usr/local

[Rainer Müller]

Ryan Schmidt wrote:
> There's an infinite number of other prefixes the user could choose  
> that would work fine. Why allow the user to use this prefix which  
> will quite probably cause them problems in the future? What benefit  
> can be obtained from using MacPorts with prefix /usr/local that  
> cannot be achieved with other prefixes?

Creating disk images/installers which install to /usr/local? ;-)

> For good measure, we should prevent installation with prefix / or / 
> usr as well, and, why not, /sw.

I think these are only invalid on Mac OS X, PureDarwin users (or users
of other OS) could use /usr, right? Not that this is common,
just for compatibility.

> [...]
> If we went with a warning instead of preventing the use of these  
> prefixes outright, when would it be printed? My concern is that there  
> is already so much output produced by configure, make and make  
> install that it's easy to overlook things.

We could add checks which abort with a big fat warning on such paths,
but can be avoided by additionally using --enable-unsafe-prefix. Would
this be a good consensus?

Rainer