cabal project override semantics proposal (#179)

Author: gbaz

content/ideas/cabal-project-semantics.md

@@ -0,0 +1,25 @@
+---
+title: improved override semantics for cabal.project files
+---
+
+The files which cabal uses to configure multipackage projects (cabal.project files) have been extended in recent years to allow includes and conditionals.
+
+This makes more common and useful situations where certain stanzas (build constraints, flags, index-state, etc) may be used to override other stanzas, rather than simply augment them. (But also, we may at times want augmenting semantics -- there's a delicate balance).
+
+The contents of different stanzas in cabal project files are monoidally accumulated. However, the monoid chosen for different stanzas has been done without much thought -- typically either with purely accumulating or purely replacement semantics.
+
+This project is for an audit of the monoidal semantics of the various setting which can be controlled by cabal.project, as well as proposal of and implementation of _more useful_ ones.
+
+Related tickets are 
+
+[https://github.com/haskell/cabal/issues/8568]
+[https://github.com/haskell/cabal/pull/9510]
+[https://github.com/haskell/cabal/issues/7556#issuecomment-1120433903]
+
+## Mentorship
+
+Gershom is willing to mentor
+
+## Difficulty and size
+
+The difficulty of implementation is medium at most, but this will require somebody who is able to thoughtfully inventory, think through, and propose the specifics of a solution, ideally with prior experience with cabal project files as a user, and also with a sense of existing user workflows. The size of the project is likely **medium**.