graphviz +rsvg depends on graphviz; circular dependency; prevents installation

[rhstanton]

On a fresh installation of MacPorts under OS X High Sierra, installation fails if I try the +rsvg variant of graphviz. Note that it seems to think it requires itself as a dependency, which seems odd:

$ sudo port install graphviz +rsvg
--->  Computing dependencies for graphviz
The following dependencies will be installed: 
 graphviz
 librsvg
 vala
Continue? [Y/n]: y
Error: Follow https://guide.macports.org/#project.tickets to report a bug.
Error: Processing of port graphviz failed

[ryandesign (Ryan Carsten Schmidt)]

Replying to rhstanton:

Note that it seems to think it requires itself as a dependency, which seems odd:

You're right. librsvg depends on vala, which depends on graphviz. So that won't work. If you want to install graphviz with the +rsvg variant, I guess you'll have to install it once without the +rsvg variant first, to satisfy vala's need.

[ryandesign (Ryan Carsten Schmidt)]

Has duplicate #56687.

[wyuenho (Jimmy Yuen Ho Wong)]

From MacPort's perspective, before installation, can't it check for cycles first, and if there's one detected, break the cycles into DAGs, and then process the DAGS successively?

[ryandesign (Ryan Carsten Schmidt)]

I have absolutely no idea. All I can tell you is that MacPorts behavior is undefined when a circular dependency exists. Please bring up the topic on the macports-dev mailing list if you have a suggestion about how we can better handle circular dependencies. Bear in mind that we have a ​rewritten MacPorts dependency engine based on libsolv implemented a couple years ago during GSoC which has not yet been merged to master; that might already change the situation.

[ryandesign (Ryan Carsten Schmidt)]

Has duplicate #58102.

[ryandesign (Ryan Carsten Schmidt)]

Has duplicate #63103.

[ballapete (Peter "Pete" Dyballa)]

Replying to ryandesign:

I have absolutely no idea. All I can tell you is that MacPorts behavior is undefined when a circular dependency exists.

In my case, #66461, it would work when port would understand that graphviz and graphviz-devel are equivalent and when there is a need to install either this or that, then install what the user wants – otherwise port would not have been invoked and could continue to sleep. If the user does not request a particular (set of) variant(s) install the default one.