Merge pull request #61843 from slavapestov/rqm-invalid-inheritance-clause

RequirementMachine: Better error recovery from invalid protocol inheritance clauses

Author: slavapestov

lib/AST/RequirementMachine/RequirementLowering.cpp

@@ -724,10 +724,28 @@ StructuralRequirementsRequest::evaluate(Evaluator &evaluator,
 
   auto selfTy = proto->getSelfInterfaceType();
 
+  unsigned errorCount = errors.size();
   realizeInheritedRequirements(proto, selfTy,
                                /*inferRequirements=*/false,
                                result, errors);
 
+  if (errors.size() > errorCount) {
+    // Add requirements from inherited protocols, which are obtained via
+    // getDirectlyInheritedNominalTypeDecls(). Normally this duplicates
+    // the information found in the resolved types from the inheritance
+    // clause, except when type resolution fails and returns an ErrorType.
+    //
+    // For example, in 'protocol P: Q & Blah', where 'Blah' does not exist,
+    // the type 'Q & Blah' resolves to an ErrorType, while the simpler
+    // mechanism in getDirectlyInheritedNominalTypeDecls() still finds 'Q'.
+    for (auto *inheritedProto : proto->getInheritedProtocols()) {
+      result.push_back({
+          Requirement(RequirementKind::Conformance,
+                      selfTy, inheritedProto->getDeclaredInterfaceType()),
+          SourceLoc(), /*wasInferred=*/false});
+    }
+  }
+
   // Add requirements from the protocol's own 'where' clause.
   WhereClauseOwner(proto).visitRequirements(TypeResolutionStage::Structural,
       [&](const Requirement &req, RequirementRepr *reqRepr) {

test/Generics/issue-61020.swift

@@ -0,0 +1,15 @@
+// RUN: %target-typecheck-verify-swift -debug-generic-signatures 2>&1 | %FileCheck %s
+
+protocol Base<T> {
+  associatedtype T
+}
+
+// CHECK-LABEL: .Derived@
+// CHECK-NEXT: Requirement signature: <Self where Self : Base>
+protocol Derived: Base & DoesNotExist { // expected-error {{cannot find type 'DoesNotExist' in scope}}
+  func position(_: T)
+}
+
+// CHECK-LABEL: .OtherDerived@
+// CHECK-NEXT: Requirement signature: <Self where Self : Base>
+protocol OtherDerived: Base<DoesNotExist> {} // expected-error {{cannot find type 'DoesNotExist' in scope}}