fix(solc): skip artifacts check for files without artifacts (#1018)

ethers-solc/src/cache.rs

@@ -638,6 +638,10 @@ impl<'a, T: ArtifactOutput> ArtifactsCacheInner<'a, T> {
                     return true
                 }
 
+                // only check artifact's existence if the file generated artifacts.
+                // e.g. a solidity file consisting only of import statements (like interfaces that
+                // re-export) do not create artifacts
+                if !entry.artifacts.is_empty() {
                     if !entry.contains_version(version) {
                         tracing::trace!(
                             "missing linked artifacts for source file `{}` for version \"{}\"",
@@ -656,6 +660,7 @@ impl<'a, T: ArtifactOutput> ArtifactsCacheInner<'a, T> {
                     }) {
                         return true
                     }
+                }
                 // all things match, can be reused
                 return false
             }

ethers-solc/tests/project.rs

@@ -683,3 +683,51 @@ fn can_recompile_with_changes() {
     assert!(compiled.find("A").is_some());
     assert!(compiled.find("B").is_some());
 }
+
+#[test]
+fn can_recompile_unchanged_with_empty_files() {
+    let tmp = TempProject::dapptools().unwrap();
+
+    tmp.add_source(
+        "A",
+        r#"
+    pragma solidity ^0.8.10;
+    import "./B.sol";
+    contract A {}
+   "#,
+    )
+    .unwrap();
+
+    tmp.add_source(
+        "B",
+        r#"
+    pragma solidity ^0.8.10;
+    import "./C.sol";
+   "#,
+    )
+    .unwrap();
+
+    let c = r#"
+    pragma solidity ^0.8.10;
+    contract C {}
+   "#;
+    tmp.add_source("C", c).unwrap();
+
+    let compiled = tmp.compile().unwrap();
+    assert!(!compiled.has_compiler_errors());
+    assert!(compiled.find("A").is_some());
+    assert!(compiled.find("C").is_some());
+
+    let compiled = tmp.compile().unwrap();
+    assert!(compiled.find("A").is_some());
+    assert!(compiled.find("C").is_some());
+    assert!(compiled.is_unchanged());
+
+    // modify C.sol
+    tmp.add_source("C", format!("{}\n", c)).unwrap();
+    let compiled = tmp.compile().unwrap();
+    assert!(!compiled.has_compiler_errors());
+    assert!(!compiled.is_unchanged());
+    assert!(compiled.find("A").is_some());
+    assert!(compiled.find("C").is_some());
+}