Merge pull request #37972 from al45tair/problem/73364629

[Runtime] Detect and log redundant subclass/superclass conformances.

Author: al45tair

stdlib/public/runtime/ProtocolConformance.cpp

@@ -906,10 +906,20 @@ swift_conformsToProtocolImpl(const Metadata *const type,
   const WitnessTable *foundWitness = nullptr;
   const Metadata *foundType = nullptr;
   for (auto searchType : iterateMaybeIncompleteSuperclasses(type)) {
-    foundWitness = foundWitnesses.lookup(searchType);
-    if (foundWitness) {
-      foundType = searchType;
-      break;
+    const WitnessTable *witness = foundWitnesses.lookup(searchType);
+    if (witness) {
+      if (!foundType) {
+        foundWitness = witness;
+        foundType = searchType;
+      } else {
+        swift::warning(RuntimeErrorFlagNone,
+                       "Warning: '%s' conforms to protocol '%s', but it also "
+                       "inherits conformance from '%s'.  Relying on a "
+                       "particular conformance is undefined behaviour.\n",
+                       foundType->getDescription()->Name.get(),
+                       protocol->Name.get(),
+                       searchType->getDescription()->Name.get());
+      }
     }
   }
 

test/multifile/Inputs/protocol-conformance-redundant-def.swift

@@ -0,0 +1,7 @@
+public protocol Hello {
+  func hello()
+}
+
+open class Super {
+  public init() {}
+}

test/multifile/Inputs/protocol-conformance-redundant-ext.swift

@@ -0,0 +1,7 @@
+import Def
+
+extension Super : Hello {
+  public func hello() {
+    print("Hello")
+  }
+}

test/multifile/protocol-conformance-redundant.swift

@@ -0,0 +1,39 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift-dylib(%t/%target-library-name(Def)) -module-name Def -emit-module -emit-module-path %t/Def.swiftmodule %S/Inputs/protocol-conformance-redundant-def.swift
+// RUN: %target-build-swift-dylib(%t/%target-library-name(Ext)) -module-name Ext -emit-module -emit-module-path %t/Ext.swiftmodule -I%t -L%t -lDef %S/Inputs/protocol-conformance-redundant-ext.swift
+// RUN: %target-build-swift -I%t -L%t -lDef -o %t/main %target-rpath(%t) %s
+// RUN: %target-codesign %t/main %t/%target-library-name(Def) %t/%target-library-name(Ext)
+// RUN: %target-run %t/main %t/%target-library-name(Ext) 2>&1 | %FileCheck %s
+
+// REQUIRES: executable_test
+// XFAIL: windows
+
+// CHECK: Warning: 'Sub' conforms to protocol 'Hello', but it also inherits conformance from 'Super'.  Relying on a particular conformance is undefined behaviour.
+// CHECK: Hello
+
+import StdlibUnittest
+
+#if canImport(Darwin)
+import Darwin
+#elseif canImport(Glibc)
+import Glibc
+#else
+#error("Unsupported platform")
+#endif
+
+import Def
+
+let dylibPath = CommandLine.arguments.last!
+let openRes = dlopen(dylibPath, RTLD_NOW|RTLD_LOCAL)
+assert(openRes != nil, "unable to open extension dylib")
+
+class Sub : Super, Hello {
+  func hello() {
+    print("Hello")
+  }
+}
+
+let s = Sub() as AnyObject as! Hello
+
+s.hello()
+