fix(solc): emit empty bytecode objects for standalone sol files (#1327)

ethers-solc/src/artifact_output/configurable.rs

@@ -339,6 +339,8 @@ impl ArtifactOutput for ConfigurableArtifacts {
         file.source_file.ast.clone().map(|ast| ConfigurableContractArtifact {
             id: Some(file.source_file.id),
             ast: Some(ast),
+            bytecode: Some(CompactBytecode::empty()),
+            deployed_bytecode: Some(CompactDeployedBytecode::empty()),
             ..Default::default()
         })
     }

ethers-solc/src/artifacts/bytecode.rs

@@ -46,6 +46,11 @@ pub struct CompactBytecode {
 }
 
 impl CompactBytecode {
+    /// Returns a new `CompactBytecode` object that contains nothing, as it's the case for
+    /// interfaces and standalone solidity files that don't contain any contract definitions
+    pub fn empty() -> Self {
+        Self { object: Default::default(), source_map: None, link_references: Default::default() }
+    }
     /// Returns the parsed source map
     ///
     /// See also <https://docs.soliditylang.org/en/v0.8.10/internals/source_mappings.html>
@@ -400,6 +405,14 @@ pub struct CompactDeployedBytecode {
     pub immutable_references: BTreeMap<String, Vec<Offsets>>,
 }
 
+impl CompactDeployedBytecode {
+    /// Returns a new `CompactDeployedBytecode` object that contains nothing, as it's the case for
+    /// interfaces and standalone solidity files that don't contain any contract definitions
+    pub fn empty() -> Self {
+        Self { bytecode: Some(CompactBytecode::empty()), immutable_references: Default::default() }
+    }
+}
+
 impl From<DeployedBytecode> for CompactDeployedBytecode {
     fn from(bcode: DeployedBytecode) -> CompactDeployedBytecode {
         CompactDeployedBytecode {