From de21ef26861db458b0dfb0212cf501f9f8ed459b Mon Sep 17 00:00:00 2001 From: Joey Hess Date: Mon, 1 Jul 2019 18:27:48 -0400 Subject: optionally use type-errors to detect stuckness Use the type-errors library to detect when the type checker gets stuck unable to reduce type-level operations on MetaTypes, and avoid displaying massive error messages in such a case. But, since type-errors is a new library not available in eg Debian yet, added a WithTypeErrors build flag. When the library is not available, cabal will automatically disable that build flag, and it will build without the type-errors library. This is most often used when combining properties of different types. If the MetaTypes don't have an OS in common, the error message used to be "Property " followed by pages of MetaTypes operations. Now it looks like this: • Cannot combine Properties: Property Property HasInfo + Debian + Buntish + ArchLinux + FreeBSD (Property is often due to a partially applied Property constructor, or due to passing the wrong type to a Property constructor.) Also it's used in ensureProperty to detect a case where the outer MetaTypes need to be inferred in order to check if the inner MetaTypes match, but the type checker is unable to infer it: • ensureProperty outer Property type is not able to be inferred here. Consider adding a type annotation. • When checking the inferred type writeConfig :: forall (outer :: [Propellor.Types.MetaTypes.MetaType]) t. And it's used in tightenTargets to detect when ghc is unable to infer the desired type of Property: • Unable to infer desired Property type in this use of tightenTargets. Consider adding a type annotation. • When checking the inferred type mk :: forall (tightened :: [Propellor.Types.MetaTypes.MetaType]). --- src/Propellor/Types.hs | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) (limited to 'src/Propellor/Types.hs') diff --git a/src/Propellor/Types.hs b/src/Propellor/Types.hs index e8e92332..026babf0 100644 --- a/src/Propellor/Types.hs +++ b/src/Propellor/Types.hs @@ -224,9 +224,16 @@ type family TightenTargetsAllowed untightened tightened where If (Targets tightened `IsSubset` Targets untightened && NonTargets untightened `IsSubset` NonTargets tightened) 'True - ( TypeError - ( 'Text "This use of tightenTargets would widen, not narrow, adding: " - ':$$: PrettyPrintMetaTypes (Difference (Targets tightened) (Targets untightened)) + (IfStuck (Targets tightened) + (TypeError + ('Text "Unable to infer desired Property type in this use of tightenTargets." + ':$$: ('Text "Consider adding a type annotation.") + ) + ) + (TypeError + ('Text "This use of tightenTargets would widen, not narrow, adding: " + ':$$: PrettyPrintMetaTypes (Difference (Targets tightened) (Targets untightened)) + ) ) ) -- cgit v1.2.3