Regression in happy 2.0: generated code uses PatternGuards without declaring it

[andreasabel]

With happy-2.0.1, I am getting this warning when building haskell-src:

[6 of 6] Compiling Language.Haskell.Parser
dist-newstyle/build/x86_64-osx/ghc-9.10.1/haskell-src-1.0.5/build/Language/Haskell/Parser.hs:4367:3: 
warning: [GHC-59119]
    accepting non-standard pattern guards
        ((Happy_GHC_Exts.tagToEnum# (off Happy_GHC_Exts.>=# 0#)) :: Bool),
        ((Happy_GHC_Exts.tagToEnum#
            (happyIndexOffAddr happyCheck off Happy_GHC_Exts.==# i)) ::
           Bool)
    Suggested fix: Perhaps you intended to use PatternGuards
     |
4367 |   | GTE(off, 0#), EQ(happyIndexOffAddr happyCheck off, i)
     |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...

The generated code is:

{-# INLINE happyIndexActionTable #-}
happyIndexActionTable i st
  | GTE(off, 0#), EQ(happyIndexOffAddr happyCheck off, i)
  = Prelude.Just (Happy_GHC_Exts.I# (happyIndexOffAddr happyTable off))
  | otherwise
  = Prelude.Nothing
  where
    off = PLUS(happyIndexOffAddr happyActOffsets st, i)

It seems to stem from the template at:

happy/lib/data/HappyTemplate.hs

Lines 90 to 97 in 17d3c93

	{-# INLINE happyIndexActionTable #-}
	happyIndexActionTable i st
	| GTE(off, 0#), EQ(happyIndexOffAddr happyCheck off, i)
	= Prelude.Just (Happy_GHC_Exts.I# (happyIndexOffAddr happyTable off))
	| otherwise
	= Prelude.Nothing
	where
	off = PLUS(happyIndexOffAddr happyActOffsets st, i)

So it is not the user's responsibility to declare LANGUAGE PatternGuards, but the one of the template.

Note that haskell-src is written in the Haskell98 language.
It could be that the happy testsuite lacks explicit Haskell98 entries, so this problem stayed under the radar.

[sgraf812]

Thanks. Indeed I could reproduce in #309 after adding -XHaskell98 to the testsuite (seems like the better default compared to implicit -XGHC20xx) and easily fixed as well. I'm preparing a release at branch release-2.0 and unless you have something to object, I will merge #309 this evening and prepare publish the new release afterwards.