Haskell IDE INLINABLE error help

Question

Have you encountered this error? IDE complains that the validator is not INLINABLE, while it actually is:

Program error: GHC Core to PLC plugin: E043:Error: Reference to a name which is not a local, a builtin, or an external INLINABLE function: Variable GHC.Base..
            No unfolding
Context: Compiling expr: GHC.Base..
Context: Compiling expr: GHC.Base..
                           @ (Plutus.V1.Ledger.Contexts.ScriptContext -> GHC.Types.Bool)
Context: Compiling expr: GHC.Base..
                           @ (Plutus.V1.Ledger.Contexts.ScriptContext -> GHC.Types.Bool)
                           @ Ledger.Typed.Scripts.Validators.WrappedMonetaryPolicyType
Context: Compiling expr: GHC.Base..
                           @ (Plutus.V1.Ledger.Contexts.ScriptContext -> GHC.Types.Bool)
                           @ Ledger.Typed.Scripts.Validators.WrappedMonetaryPolicyType
                           @ Plutus.V1.Ledger.Value.TokenName
Context: Compiling expr: GHC.Base..
                           @ (Plutus.V1.Ledger.Contexts.ScriptContext -> GHC.Types.Bool)
                           @ Ledger.Typed.Scripts.Validators.WrappedMonetaryPolicyType
                           @ Plutus.V1.Ledger.Value.TokenName
                           Ledger.Typed.Scripts.Validators.wrapMonetaryPolicy
Context: Compiling expr: GHC.Base..
                           @ (Plutus.V1.Ledger.Contexts.ScriptContext -> GHC.Types.Bool)
                           @ Ledger.Typed.Scripts.Validators.WrappedMonetaryPolicyType
                           @ Plutus.V1.Ledger.Value.TokenName
                           Ledger.Typed.Scripts.Validators.wrapMonetaryPolicy
                           Plutus.Contracts.FungibleToken.validator
Context: Compiling expr at "main:Plutus.Contracts.FungibleToken:(19,6)-(19,69)"

Module I'm trying to use IDE in:

{-# LANGUAGE DataKinds       #-}
{-# LANGUAGE TemplateHaskell #-}

module Plutus.Contracts.FungibleToken where

import           Ledger.Typed.Scripts      (MonetaryPolicy)
import qualified Ledger.Typed.Scripts      as Scripts
import           Plutus.V1.Ledger.Contexts (ScriptContext)
import qualified Plutus.V1.Ledger.Scripts  as Scripts
import           Plutus.V1.Ledger.Value    (TokenName, Value)
import qualified PlutusTx

{-# INLINABLE validator #-}
validator :: TokenName -> ScriptContext -> Bool
validator _ _ = True

makeLiquidityPolicy :: TokenName -> MonetaryPolicy
makeLiquidityPolicy tokenName = Scripts.mkMonetaryPolicyScript $
  $$(PlutusTx.compile [|| Scripts.wrapMonetaryPolicy . validator ||])
    `PlutusTx.applyCode`
        PlutusTx.liftCode tokenName

Answer 1

The pragma {-# LANGUAGE NoImplicitPrelude #-} and import PlutusTx.Prelude might help.

It replaces the implicitly defined functions in Haskell by inlinable alternatives. Here is an example for Boolean operators.

Answer 2

The way HLS is enabled without plugin errors is discussed here:

• https://github.com/input-output-hk/plutus-starter/pull/23
• https://github.com/input-output-hk/plutus-starter/pull/29
• https://github.com/input-output-hk/plutus/issues/3454

Basically, you need to enable defer-plugin-errors flag. You can do this with following command:

cabal configure -f defer-plugin-errors

Remember to turn it off when you actually need to check if validators are compiled properly. This resets configuration:

cabal configure