Error on cabal sandbox-configure with "installed" constraint

[bmillwood]

I have the following in my .cabal/config:

constraint: template-haskell installed

When I do a cabal sandbox-init I get a cabal.sandbox.config containing the following lines:

-- inherit:
constraints: template-haskell installed

Then cabal sandbox-configure says:

cabal: Error parsing package environment file
/home/ben/haskell/fay/cabal.sandbox.config:15:
Ambiguous parse in field 'constraints'.

With a constraint other than installed (specifying the version, for example), it works fine.

[23Skidoo]

Thanks, will look into this.

[23Skidoo]

Interesting: parsing "template-haskell installed" with readUserConstraint returns UserConstraintInstalled (PackageName "template-haskell"), but parsing the same string with parse returns [UserConstraintInstalled (PackageName "template-haskell"),UserConstraintFlags (PackageName "template-haskell") [(FlagName "installed",True)]].

Looks like the ambiguity was always there, and I just triggered it by using parseCommaList parse.

[23Skidoo]

The bug was caused by missing parentheses in the UserConstraint parser: +++ and <++ are right-associative, so a +++ b +++ c <++ d is parsed as (a +++ (b +++ (c <++ d))).