Stan 0206 should not fire for type data

[noughtmare]

I have this code:

{-# LANGUAGE TypeData #-}

infixr :->
type data PCFType = PCFType :-> PCFType | Nat

And Stan reports:

 ✲ Name:        Data types with non-strict fields
 ✲ Description: Defining lazy fields in data types can lead to unexpected space leaks
 ✲ Severity:    Performance
 ✲ Category:    #SpaceLeak #Syntax
Possible solutions:
  - Add '!' before the type, e.g. !Int or !(Maybe Bool)
  - Enable the 'StrictData' extension: {-# LANGUAGE StrictData #-}
stan(STAN-0206)

But strictness fields are not allowed in type data declarations.

[tomjaguarpaw]

Thanks, I agree this is a bug. I suspect it will only be fixed if there's a volunteer contribution.

[noughtmare]

I've looked into it a bit and I think the change should be somewhere here:

stan/src/Stan/Analysis/Analyser.hs

Lines 167 to 180 in ddcd461

	matchLazyField node = memptyIfFalse
	-- return empty list if it's not a data type
	(hieMatchPatternAst hie node dataDecl)
	-- get list of all constructors
	$ let constructors = filter
	(\n -> hieMatchPatternAst hie n constructor)
	(nodeChildren node)
	in case constructors of
	-- no constructors = not observations
	[] -> mempty
	-- single constructor
	[c] -> S.concatMap matchField $ extractFields False c
	-- multiple constructors = analyse everything
	cs -> S.concatMap (S.concatMap matchField . extractFields True) cs

But I don't quite know what to change yet.