Fix zero-arg builtins invokations.

There are currently two zero-arg builtins:

  - mkNilData
  - mkNilPairData

  And while they have strictly speaking no arguments, the VM still
  requires that they are called with an extra unit argument applied.

crates/aiken-lang/src/gen_uplc.rs

@@ -4066,10 +4066,16 @@ impl<'a> CodeGenerator<'a> {
                     builtin,
                     ..
                 } => {
-                    assert!(
-                        builtin.is_none(),
-                        "found remaining builtin function {func_name:?} ({builtin:?} declared as a module function in {module:?}"
-                    );
+                    if let Some(func) = builtin {
+                        return self.gen_uplc(
+                            Air::Builtin {
+                                count: 0,
+                                func: *func,
+                                tipo: constructor.tipo,
+                            },
+                            arg_stack,
+                        );
+                    }
 
                     if let Some((names, index, cyclic_name)) = self.cyclic_functions.get(&(
                         FunctionAccessKey {
@@ -4490,8 +4496,12 @@ impl<'a> CodeGenerator<'a> {
 
                         term = builder::apply_builtin_forces(term, func.force_count());
 
-                        for arg in arg_vec {
-                            term = term.apply(arg.clone());
+                        if func.arg_is_unit() {
+                            term = term.apply(Term::unit())
+                        } else {
+                            for arg in arg_vec {
+                                term = term.apply(arg.clone());
+                            }
                         }
 
                         term

crates/aiken-project/src/tests/gen_uplc.rs

@@ -6562,3 +6562,41 @@ fn mk_cons_direct_invoke_3() {
         false,
     )
 }
+
+#[test]
+fn mk_nil_pair_data() {
+    let src = r#"
+        use aiken/builtin.{mk_nil_pair_data}
+
+        test nil_equals() {
+            mk_nil_pair_data() == mk_nil_pair_data()
+        }
+    "#;
+
+    assert_uplc(
+        src,
+        Term::equals_data()
+            .apply(Term::map_data().apply(Term::mk_nil_pair_data().apply(Term::unit())))
+            .apply(Term::map_data().apply(Term::mk_nil_pair_data().apply(Term::unit()))),
+        false,
+    )
+}
+
+#[test]
+fn mk_nil_list_data() {
+    let src = r#"
+        use aiken/builtin.{mk_nil_data}
+
+        test nil_equals() {
+            mk_nil_data() == mk_nil_data()
+        }
+    "#;
+
+    assert_uplc(
+        src,
+        Term::equals_data()
+            .apply(Term::list_data().apply(Term::mk_nil_data().apply(Term::unit())))
+            .apply(Term::list_data().apply(Term::mk_nil_data().apply(Term::unit()))),
+        false,
+    )
+}

crates/uplc/src/machine/runtime.rs

@@ -1,23 +1,20 @@
-use std::{mem::size_of, ops::Deref, rc::Rc};
-
-use num_bigint::BigInt;
-use num_integer::Integer;
-use num_traits::{Signed, Zero};
-use once_cell::sync::Lazy;
-use pallas_primitives::conway::{Language, PlutusData};
-
+use super::{
+    cost_model::{BuiltinCosts, ExBudget},
+    value::{from_pallas_bigint, to_pallas_bigint},
+    Error, Value,
+};
 use crate::{
     ast::{Constant, Data, Type},
     builtins::DefaultFunction,
     machine::value::integer_log2,
     plutus_data_to_bytes,
 };
-
-use super::{
-    cost_model::{BuiltinCosts, ExBudget},
-    value::{from_pallas_bigint, to_pallas_bigint},
-    Error, Value,
-};
+use num_bigint::BigInt;
+use num_integer::Integer;
+use num_traits::{Signed, Zero};
+use once_cell::sync::Lazy;
+use pallas_primitives::conway::{Language, PlutusData};
+use std::{mem::size_of, ops::Deref, rc::Rc};
 
 static SCALAR_PERIOD: Lazy<BigInt> = Lazy::new(|| {
     BigInt::from_bytes_be(
@@ -111,6 +108,85 @@ impl From<DefaultFunction> for BuiltinRuntime {
 }
 
 impl DefaultFunction {
+    pub fn arg_is_unit(&self) -> bool {
+        match self {
+            DefaultFunction::MkNilData | DefaultFunction::MkNilPairData => true,
+            DefaultFunction::AddInteger
+            | DefaultFunction::SubtractInteger
+            | DefaultFunction::MultiplyInteger
+            | DefaultFunction::DivideInteger
+            | DefaultFunction::QuotientInteger
+            | DefaultFunction::RemainderInteger
+            | DefaultFunction::ModInteger
+            | DefaultFunction::EqualsInteger
+            | DefaultFunction::LessThanInteger
+            | DefaultFunction::LessThanEqualsInteger
+            | DefaultFunction::AppendByteString
+            | DefaultFunction::ConsByteString
+            | DefaultFunction::SliceByteString
+            | DefaultFunction::LengthOfByteString
+            | DefaultFunction::IndexByteString
+            | DefaultFunction::EqualsByteString
+            | DefaultFunction::LessThanByteString
+            | DefaultFunction::LessThanEqualsByteString
+            | DefaultFunction::Sha2_256
+            | DefaultFunction::Sha3_256
+            | DefaultFunction::Blake2b_224
+            | DefaultFunction::Blake2b_256
+            | DefaultFunction::Keccak_256
+            | DefaultFunction::VerifyEd25519Signature
+            | DefaultFunction::VerifyEcdsaSecp256k1Signature
+            | DefaultFunction::VerifySchnorrSecp256k1Signature
+            | DefaultFunction::AppendString
+            | DefaultFunction::EqualsString
+            | DefaultFunction::EncodeUtf8
+            | DefaultFunction::DecodeUtf8
+            | DefaultFunction::IfThenElse
+            | DefaultFunction::ChooseUnit
+            | DefaultFunction::Trace
+            | DefaultFunction::FstPair
+            | DefaultFunction::SndPair
+            | DefaultFunction::ChooseList
+            | DefaultFunction::MkCons
+            | DefaultFunction::HeadList
+            | DefaultFunction::TailList
+            | DefaultFunction::NullList
+            | DefaultFunction::ChooseData
+            | DefaultFunction::ConstrData
+            | DefaultFunction::MapData
+            | DefaultFunction::ListData
+            | DefaultFunction::IData
+            | DefaultFunction::BData
+            | DefaultFunction::UnConstrData
+            | DefaultFunction::UnMapData
+            | DefaultFunction::UnListData
+            | DefaultFunction::UnIData
+            | DefaultFunction::UnBData
+            | DefaultFunction::EqualsData
+            | DefaultFunction::SerialiseData
+            | DefaultFunction::MkPairData
+            | DefaultFunction::Bls12_381_G1_Add
+            | DefaultFunction::Bls12_381_G1_Neg
+            | DefaultFunction::Bls12_381_G1_ScalarMul
+            | DefaultFunction::Bls12_381_G1_Equal
+            | DefaultFunction::Bls12_381_G1_Compress
+            | DefaultFunction::Bls12_381_G1_Uncompress
+            | DefaultFunction::Bls12_381_G1_HashToGroup
+            | DefaultFunction::Bls12_381_G2_Add
+            | DefaultFunction::Bls12_381_G2_Neg
+            | DefaultFunction::Bls12_381_G2_ScalarMul
+            | DefaultFunction::Bls12_381_G2_Equal
+            | DefaultFunction::Bls12_381_G2_Compress
+            | DefaultFunction::Bls12_381_G2_Uncompress
+            | DefaultFunction::Bls12_381_G2_HashToGroup
+            | DefaultFunction::Bls12_381_MillerLoop
+            | DefaultFunction::Bls12_381_MulMlResult
+            | DefaultFunction::Bls12_381_FinalVerify
+            | DefaultFunction::IntegerToByteString
+            | DefaultFunction::ByteStringToInteger => false,
+        }
+    }
+
     pub fn arity(&self) -> usize {
         match self {
             DefaultFunction::AddInteger => 2,