[SymbolGraph] Look at inherited protocols for default implementations

lib/SymbolGraphGen/SymbolGraph.cpp

@@ -253,19 +253,29 @@ SymbolGraph::recordInheritanceRelationships(Symbol S) {
 }
 
 void SymbolGraph::recordDefaultImplementationRelationships(Symbol S) {
-  const auto VD = S.getSymbolDecl();
-  if (const auto *Extension = dyn_cast<ExtensionDecl>(VD->getDeclContext())) {
-    if (const auto *Protocol = Extension->getExtendedProtocolDecl()) {
-      for (const auto *Member : Protocol->getMembers()) {
-        if (const auto *MemberVD = dyn_cast<ValueDecl>(Member)) {
-          if (MemberVD->getFullName().compare(VD->getFullName()) == 0) {
-            recordEdge(Symbol(this, VD, nullptr),
-                       Symbol(this, MemberVD, nullptr),
-                       RelationshipKind::DefaultImplementationOf());
-          }
+  const auto *VD = S.getSymbolDecl();
+
+  /// Claim a protocol `P`'s members as default implementation targets
+  /// for `VD`.
+  auto HandleProtocol = [=](const ProtocolDecl *P) {
+    for (const auto *Member : P->getMembers()) {
+      if (const auto *MemberVD = dyn_cast<ValueDecl>(Member)) {
+        if (MemberVD->getFullName().compare(VD->getFullName()) == 0) {
+          recordEdge(Symbol(this, VD, nullptr),
+                     Symbol(this, MemberVD, nullptr),
+                     RelationshipKind::DefaultImplementationOf());
         }
       }
     }
+  };
+
+  if (const auto *Extension = dyn_cast<ExtensionDecl>(VD->getDeclContext())) {
+    if (const auto *ExtendedProtocol = Extension->getExtendedProtocolDecl()) {
+      HandleProtocol(ExtendedProtocol);
+      for (const auto *Inherited : ExtendedProtocol->getInheritedProtocols()) {
+        HandleProtocol(Inherited);
+      }
+    }
   }
 }
 

test/SymbolGraph/Relationships/ConformsTo/Basic.swift

@@ -0,0 +1,16 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -module-name Basic -emit-module -emit-module-path %t/
+// RUN: %target-swift-symbolgraph-extract -module-name Basic -I %t -pretty-print -output-dir %t
+// RUN: %FileCheck %s --input-file %t/Basic.symbols.json
+
+public protocol P {
+  var x: Int { get }
+}
+
+public struct S: P {
+  public var x: Int
+}
+
+// CHECK: "kind": "conformsTo"
+// CHECK-NEXT: "source": "s:5Basic1SV"
+// CHECK-NEXT: "target": "s:5Basic1PP"

test/SymbolGraph/Relationships/ConformsTo/Indirect.swift

@@ -0,0 +1,23 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -module-name Indirect -emit-module -emit-module-path %t/
+// RUN: %target-swift-symbolgraph-extract -module-name Indirect -I %t -pretty-print -output-dir %t
+// RUN: %FileCheck %s --input-file %t/Indirect.symbols.json
+
+public protocol P {
+  func foo()
+}
+
+public protocol Q : P {}
+
+public struct S : Q {
+  public func foo() {}
+}
+
+// Q : P
+// CHECK-DAG: "kind": "conformsTo",{{[[:space:]]*}}"source": "s:8Indirect1QP",{{[[:space:]]*}}"target": "s:8Indirect1PP"
+
+// S : P
+// CHECK-DAG: "kind": "conformsTo",{{[[:space:]]*}}"source": "s:8Indirect1SV",{{[[:space:]]*}}"target": "s:8Indirect1PP"
+
+// S : Q
+// CHECK-DAG: "kind": "conformsTo",{{[[:space:]]*}}"source": "s:8Indirect1SV",{{[[:space:]]*}}"target": "s:8Indirect1QP"

test/SymbolGraph/Relationships/DefaultImplementationOf/Indirect.swift

@@ -0,0 +1,17 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -module-name Indirect -emit-module -emit-module-path %t/
+// RUN: %target-swift-symbolgraph-extract -module-name Indirect -I %t -pretty-print -output-dir %t
+// RUN: %FileCheck %s --input-file %t/Indirect.symbols.json
+
+public protocol P {
+  associatedtype Thing
+  func foo()
+}
+
+public protocol Q : P {}
+
+extension Q {
+  public func foo() {}
+}
+
+// CHECK-DAG: "kind": "defaultImplementationOf",{{[[:space:]]*}}"source": "s:8Indirect1QPAAE3fooyyF",{{[[:space:]]*}}"target": "s:8Indirect1PP3fooyyF"