Fix crash caused by cyclic inherited type references. Closes #364 (#365)

CHANGELOG.md

@@ -10,7 +10,7 @@
 
 ##### Bug Fixes
 
-- None.
+- Fix crash caused by cyclic inherited type references.
 
 ## 2.7.0 (2021-06-29)
 

Sources/PeripheryKit/Indexer/SourceGraph.swift

@@ -200,14 +200,19 @@ public final class SourceGraph {
         try visitor.make(graph: self).visit()
     }
 
-    func inheritedTypeReferences(of decl: Declaration) -> [Reference] {
+    func inheritedTypeReferences(of decl: Declaration, seenDeclarations: Set<Declaration> = []) -> [Reference] {
         var references: [Reference] = []
 
         for reference in decl.immediateInheritedTypeReferences {
             references.append(reference)
 
             if let inheritedDecl = explicitDeclaration(withUsr: reference.usr) {
-                references = inheritedTypeReferences(of: inheritedDecl) + references
+                // Detect circular references. The following is valid Swift.
+                // class SomeClass {}
+                // extension SomeClass: SomeProtocol {}
+                // protocol SomeProtocol: SomeClass {}
+                guard !seenDeclarations.contains(inheritedDecl) else { continue }
+                references = inheritedTypeReferences(of: inheritedDecl, seenDeclarations: seenDeclarations.union([decl])) + references
             }
         }
 

Tests/Fixtures/RetentionFixtures/testCircularTypeInheritance.swift

@@ -0,0 +1,5 @@
+import Foundation
+
+class FixtureClass211 {}
+extension FixtureClass211: FixtureProtocol211 {}
+protocol FixtureProtocol211: FixtureClass211 {}

Tests/PeripheryTests/RetentionTest.swift

@@ -1241,6 +1241,13 @@ final class RetentionTest: SourceGraphTestCase {
         }
     }
 
+    func testCircularTypeInheritance() {
+        analyze {
+            // Intentionally blank.
+            // Fixture contains a circular reference that shouldn't cause a stack overflow.
+        }
+    }
+
     // MARK: - Objective-C
 
     #if os(macOS)