Allow set notation in `allow-newer`

[andreasabel]

$ cabal build --allow-newer='aeson:{base,ghc-prim}'
Error: cabal: invalid argument to option `--allow-newer': Cannot parse the
list of packages: aeson:{base,ghc-prim}

Would be nice if this would be expanded in the obvious way.

In general, in --allow-newer=P:D, P:D could mean the cartesian product of sets P and D.

Related: #7740

[josephcsible]

If you omit the single quotes, won't this already do what you want due to the shell's expansion of curly braces?

[andreasabel]

Indeed, at least in bash: https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Brace-Expansion
Learned something new!
But this wouldn't work then if I call cabal directly, or via powershell, or...

[philderbeast]

This set notation could also be used in project files.

[ulysses4ever]

For a future volunteer taking up this ticket: does anyone have a place in cabal syntax in mind that already supports set syntax?