Troubleshooting

Compilation Errors

"No unfolding"

This means the plugin cannot access to the definition of a Haskell identifier, which it needs to be able to compile that identifier to Plutus Core.

If the identifier in question is defined in the source code, try adding the INLINABLE pragma to it (not the INLINE pragma, which should generally be avoided). If it already has the INLINABLE pragma, try adding the GHC flags -fno-ignore-interface-pragmas and -fno-omit-interface-pragmas.

If this doesn't resolve the issue, or if the identifier in question isn't directly defined in the code but is produced by GHC optimizations, ensure that you apply all GHC flags listed in Compiling Plutus Tx. These flags disable GHC optimizations that can interfere with the plugin, and ensure that unfoldings are neither omitted nor ignored.

If the identifier with missing unfolding is from base or invoked by a function from base, you should use instead the corresponding function from the plutus-tx package. Note that the plugin lacks support for certain functions and methods from base.

This error can also occur if the identifier simply doesn't have an unfolding, e.g., f x = $$(compile [|| x + 1 ||]). Clearly there is no unfolding for x, so it is impossible for it to work.

Alternatively, this error may happen when using GHCi, which is not fully supported by the plugin. Not only does GHCi often hide unfoldings from the plugin, but it may also introduce debugging information like breakpoints in GHC Core, causing the plugin to fail.

"Unsupported feature: Cannot case on a value on type: {type}"

If {type} is a builtin type like BuiltinBool: to convert a builtin type to the corresponding Haskell type (such as BuiltinBool to Bool or BuiltinList to a Haskell list) in Plutus Tx, you should use fromOpaque. Pattern matching on the builtin type or using fromBuiltin is not permitted, and will lead to the above error.

If {type} is a GHC type like GHC.Num.Integer.Integer: you may be using operations from base (such as GHC.Classes.==) on that type, or using a literal of that type in a pattern. An example of the latter:

case (x :: Maybe Integer) of Just 42 -> ...

This is not supported, and you should instead write

case (x :: Maybe Integer) of Just y | y PlutusTx.== 42 -> ...

"Unsupported feature: Cannot construct a value of type"

Conversely, to convert a Haskell type to the correspoding builtin type in Plutus Tx, you should use toOpaque, rather than directly using the data constructor or toBuiltin.

Runtime Issues

Missing Trace Messages

If your expected trace messages are missing, check the following plugin flags:

• If the remove-trace flag (default off) is on, all trace messages will be removed.
• If the preserve-logging flag (default off) is off, the compiler may remove some trace messages during optimization.

Unexpected Evaluation Failure

It is usually advisable to use the Strict extension when writing Plutus Tx, which improves performance. However, be cautious, as this can result in unexpected evaluation failures. Consider the following script:

{-# LANGUAGE Strict #-}

data MyRedeemer = A | B

myScript :: MyRedeemer -> ScriptContext -> Bool
myScript redeemer ctx = case redeemer of
  A -> condition1
  B -> condition2
  where
    condition1, condition2 :: Bool
    condition1 = ...
    condition2 = if ... then True else traceError "condition 2 not met"

The Strict extension makes all bindings strict, which means even if redeemer matches A, condition2 will still be evaluated. This can be inefficient at best and, at worst, cause unexpected failures if condition2 is not met when the redeemer matches A.

There are multiple ways to fix this:

1. You can make condition1 and condition2 non-strict by adding tildes:

~condition1 = ...
~condition2 = ...

2. Alternatively, you can define condition1 and condition2 within the case branches:

case redeemer of
  A -> let condition1 = ... in condition1
  B -> let condition2 = ... in condition2

3. Another option is to turn condition1 and condition2 into functions that take some arguments and return a Bool, as functions are not evaluated until all their arguments are provided.

Haddock

The plugin will typically fail when producing Haddock documentation. However, in this instance, you can simply tell it to defer any errors to runtime, using the defer-errors plugin flag. Since you are only building documentation, runtime errors won't occur.

Error codes

Some Plutus Tx library functions produce error messages when failing. To reduce code size, error codes are used instead of full error messages. The mapping from error codes to error messages can be found in PlutusTx.ErrorCodes.