fix: Using the wrong match string for discards in FieldsExpose

Also need to return a lambda wrapped term from list_access_to_uplc under all conditions

crates/aiken-lang/src/gen_uplc.rs

@@ -4985,7 +4985,7 @@ impl<'a> CodeGenerator<'a> {
 
                 let named_indices = names_types
                     .iter()
-                    .skip_while(|(name, _, _)| name.is_empty())
+                    .skip_while(|(name, _, _)| name == "_")
                     .collect_vec();
 
                 if !named_indices.is_empty() || is_expect {

crates/aiken-lang/src/gen_uplc/builder.rs

@@ -1538,13 +1538,14 @@ pub fn list_access_to_uplc(
         .collect_vec();
 
     // If the the is just discards and check_last_item then we check for empty list
-    if no_tailing_discards.is_empty()
+    if no_tailing_discards.is_empty() {
-        && !tail_present
+        if !tail_present && matches!(expect_level, ExpectLevel::Full | ExpectLevel::Items) {
-        && matches!(expect_level, ExpectLevel::Full | ExpectLevel::Items)
-    {
             return Term::var("empty_list")
                 .delayed_choose_list(term, error_term)
                 .lambda("empty_list");
+        } else {
+            return term.lambda("_");
+        }
     }
 
     // reverse back to original order
@@ -1585,15 +1586,21 @@ pub fn list_access_to_uplc(
                 // case for no tail
                 // name is guaranteed to not be discard at this point
 
-                if matches!(expect_level, ExpectLevel::None)
+                match expect_level {
-                    || (error_term == Term::Error && tail_present)
+                    ExpectLevel::None => acc.lambda(name).apply(head_list).lambda(tail_name),
-                {
+                    ExpectLevel::Full | ExpectLevel::Items => {
+                        if error_term == Term::Error && tail_present {
                             acc.lambda(name).apply(head_list).lambda(tail_name)
                         } else if tail_present {
+                            // Custom error instead of trying to do head_list on a possibly empty list.
                             Term::var(tail_name.to_string())
-                        .delayed_choose_list(error_term.clone(), acc.lambda(name).apply(head_list))
+                                .delayed_choose_list(
+                                    error_term.clone(),
+                                    acc.lambda(name).apply(head_list),
+                                )
                                 .lambda(tail_name)
                         } else if error_term == Term::Error {
+                            // Check head is last item in this list
                             Term::tail_list()
                                 .apply(Term::var(tail_name.to_string()))
                                 .delayed_choose_list(acc, error_term.clone())
@@ -1601,6 +1608,7 @@ pub fn list_access_to_uplc(
                                 .apply(head_list)
                                 .lambda(tail_name)
                         } else {
+                            // Custom error if list is not empty after this head
                             Term::var(tail_name.to_string())
                                 .delayed_choose_list(
                                     error_term.clone(),
@@ -1612,6 +1620,8 @@ pub fn list_access_to_uplc(
                                 )
                                 .lambda(tail_name)
                         }
+                    }
+                }
             } else if name == "_" {
                 if matches!(expect_level, ExpectLevel::None) || error_term == Term::Error {
                     acc.apply(Term::tail_list().apply(Term::var(tail_name.to_string())))

examples/acceptance_tests/089/aiken.lock

@@ -13,4 +13,4 @@ requirements = []
 source = "github"
 
 [etags]
-"aiken-lang/stdlib@main" = [{ secs_since_epoch = 1705743642, nanos_since_epoch = 175324000 }, "cf946239d3dd481ed41f20e56bf24910b5229ea35aa171a708edc2a47fc20a7b"]
+"aiken-lang/stdlib@main" = [{ secs_since_epoch = 1706206922, nanos_since_epoch = 401031000 }, "cf946239d3dd481ed41f20e56bf24910b5229ea35aa171a708edc2a47fc20a7b"]

examples/acceptance_tests/089/validators/test2.ak

@@ -0,0 +1,77 @@
+use aiken/list
+use aiken/transaction.{
+  Input, Mint, NoDatum, Output, OutputReference, ScriptContext, Transaction,
+  TransactionId,
+}
+use aiken/transaction/credential.{Address, VerificationKeyCredential}
+use aiken/transaction/value
+
+pub const own_hash = #"01020304050607080910111213140102030405060708091011121314"
+
+pub const other_hash =
+  #"02030405060708091011121314150203040506070809101112131415"
+
+pub const beneficiary_keyhash =
+  #"03040506070809101112131415160304050607080910111213141516"
+
+pub fn beneficiary_address() {
+  keyhash_address(beneficiary_keyhash)
+}
+
+pub fn keyhash_address(keyhash: ByteArray) {
+  Address {
+    payment_credential: VerificationKeyCredential(keyhash),
+    stake_credential: None,
+  }
+}
+
+validator(utxo_ref: OutputReference) {
+  fn simple_oneshot(_r: Void, ctx: ScriptContext) -> Bool {
+    let ScriptContext { transaction, purpose } = ctx
+    let Transaction { inputs, .. } = transaction
+
+    trace @"Here"
+
+    
+    expect Mint(_policy_id) = purpose
+
+    trace @"Here1"
+
+    
+    expect Some(_input) =
+      list.find(inputs, fn(input) { input.output_reference == utxo_ref })
+
+    trace @"Here2"
+
+    True
+      
+    
+  }
+}
+
+test test_simple_oneshot() {
+  let output =
+    Output {
+      address: beneficiary_address(),
+      value: value.zero(),
+      datum: NoDatum,
+      reference_script: None,
+    }
+
+  let val =
+    value.from_asset(policy_id: own_hash, asset_name: "testtoken", quantity: 1)
+  let utxo =
+    OutputReference { transaction_id: TransactionId(""), output_index: 0 }
+
+  let input = Input { output_reference: utxo, output }
+
+  let tx =
+    Transaction {
+      ..transaction.placeholder(),
+      mint: value.to_minted_value(val),
+      extra_signatories: [other_hash],
+      inputs: [input],
+    }
+  let context = ScriptContext { purpose: Mint(own_hash), transaction: tx }
+  simple_oneshot(utxo, Void, context) == True
+}