Fix to issue 1062: Follow property type references from child declarations when marking

Sources/SourceGraph/Mutators/UsedDeclarationMarker.swift

@@ -66,6 +66,17 @@ final class UsedDeclarationMarker: SourceGraphMutator {
             for ref in declaration.related {
                 markUsed(declarationsReferenced(by: ref))
             }
+
+            // Follow type references from child property declarations.
+            // Property type references are associated with the property declaration
+            // by the indexer, not the containing type. Walking varType references
+            // ensures types used as property types are marked used when the parent
+            // type is used.
+            for childDecl in declaration.declarations where childDecl.kind.isVariableKind {
+                for ref in childDecl.references where ref.role == .varType {
+                    markUsed(declarationsReferenced(by: ref))
+                }
+            }
         }
     }
 

Tests/Fixtures/Sources/RetentionFixtures/testRetainsPropertyTypeReferencesOfUsedDeclaration.swift

@@ -0,0 +1,18 @@
+import Foundation
+
+struct FixtureItem222: Identifiable, Hashable {
+    let id: UUID
+    let name: String
+}
+
+public struct FixtureViewModel222 {
+    struct FixtureSection222: Identifiable, Hashable {
+        let id: UUID
+        var equipment: [FixtureItem222]
+    }
+    var sections: [FixtureSection222] = []
+
+    public mutating func addSection() {
+        sections.append(FixtureSection222(id: UUID(), equipment: []))
+    }
+}

Tests/Fixtures/Sources/RetentionFixtures/testRetainsStaticMethodOnExternalTypeExtension.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+public class FixtureClassStaticExtMethod {
+    public func someMethod() {
+        let _ = [Int].emptyArray()
+        let _ = [String].constrainedFactory("hello")
+        NumberFormatter.customFormat()
+    }
+}
+
+extension Array {
+    static func emptyArray() -> [Any] { [] }
+}
+
+extension Array where Element == String {
+    static func constrainedFactory(_ value: String) -> [String] { [value] }
+}
+
+extension NumberFormatter {
+    static func customFormat() {}
+}

Tests/PeripheryTests/RetentionTest.swift

@@ -594,6 +594,23 @@ final class RetentionTest: FixtureSourceGraphTestCase {
         }
     }
 
+    func testRetainsStaticMethodOnExternalTypeExtension() {
+        analyze(retainPublic: true) {
+            assertReferenced(.class("FixtureClassStaticExtMethod")) {
+                self.assertReferenced(.functionMethodInstance("someMethod()"))
+            }
+            assertReferenced(.extensionStruct("Array", line: 11)) {
+                self.assertReferenced(.functionMethodStatic("emptyArray()"))
+            }
+            assertReferenced(.extensionStruct("Array", line: 15)) {
+                self.assertReferenced(.functionMethodStatic("constrainedFactory(_:)"))
+            }
+            assertReferenced(.extensionClass("NumberFormatter", line: 19)) {
+                self.assertReferenced(.functionMethodStatic("customFormat()"))
+            }
+        }
+    }
+
     func testRetainsExtendedTypeAlias() {
         analyze(retainPublic: true) {
             assertReferenced(.typealias("Fixture214TypeAlias"))
@@ -848,7 +865,14 @@ final class RetentionTest: FixtureSourceGraphTestCase {
             assertReferenced(.class("FixtureClass71")) {
                 self.assertNotReferenced(.varInstance("someVar"))
             }
-            assertNotReferenced(.class("FixtureClass72"))
+            assertReferenced(.class("FixtureClass72"))
+        }
+    }
+
+    func testRetainsPropertyTypeReferencesOfUsedDeclaration() {
+        analyze(retainPublic: true) {
+            assertReferenced(.struct("FixtureViewModel222"))
+            assertReferenced(.struct("FixtureItem222"))
         }
     }