piecrust: use empty constructor arguments by default

Previously we were erroring out when providing no arguments for a
constructor that takes no argument. This is undesirable since downstream
does not necessarily know that the contract they deploy has a constructor.

A contract that is provided an argument that it doesn't expect will
still error at deploy time, during execution of the constructor.

Resolves #316

piecrust/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Use empty constructor arguments by default [#316]
 - Upgrade `dusk-wasmtime` to version `18`
 
 ## [0.16.0] - 2024-02-14
@@ -366,6 +367,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 <!-- ISSUES -->
 [#325]: https://github.com/dusk-network/piecrust/issues/325
 [#324]: https://github.com/dusk-network/piecrust/issues/324
+[#316]: https://github.com/dusk-network/piecrust/issues/316
 [#301]: https://github.com/dusk-network/piecrust/issues/313
 [#301]: https://github.com/dusk-network/piecrust/issues/301
 [#296]: https://github.com/dusk-network/piecrust/issues/296

piecrust/src/session.rs

@@ -289,22 +289,13 @@ impl Session {
             let instance =
                 self.instance(&contract_id).expect("instance should exist");
 
-            let has_init = instance.is_function_exported(INIT_METHOD);
-            if has_init && arg.is_none() {
-                return Err(InitalizationError(
-                    "Contract has constructor but no argument was provided"
-                        .into(),
-                ));
-            }
-
-            if let Some(arg) = arg {
-                if !has_init {
-                    return Err(InitalizationError(
-                        "Argument was provided but contract has no constructor"
-                            .into(),
-                    ));
-                }
-
+            if instance.is_function_exported(INIT_METHOD) {
+                // If no argument was provided, we call the constructor anyway,
+                // but with an empty argument. The alternative is to panic, but
+                // that assumes that the caller of `deploy` knows that the
+                // contract has a constructor in the first place, which might
+                // not be the case, such as when ingesting untrusted bytecode.
+                let arg = arg.unwrap_or_default();
                 self.call_inner(contract_id, INIT_METHOD, arg, gas_limit)?;
             }
 

piecrust/tests/constructor.rs

@@ -73,20 +73,20 @@ fn constructor() -> Result<(), Error> {
 }
 
 #[test]
-fn missing_init() -> Result<(), Error> {
+fn empty_constructor_argument() -> Result<(), Error> {
     let vm = VM::ephemeral()?;
 
     let mut session = vm.session(SessionData::builder())?;
 
-    let result = session.deploy(
-        contract_bytecode!("counter"),
-        ContractData::builder(OWNER).constructor_arg(&0xabu8),
+    let id = session.deploy(
+        contract_bytecode!("empty_constructor"),
+        ContractData::builder(OWNER),
         LIMIT,
-    );
+    )?;
 
-    assert!(
-        result.is_err(),
-        "deploy with data when the 'init' method is not exported should fail with an error"
+    assert_eq!(
+        session.call::<_, u8>(id, "read_value", &(), LIMIT)?.data,
+        0x10
     );
 
     Ok(())