Sema: Check generic parameter inheritance clause after creating archetype

This fixes a crash with invalid code where the inheritance clause
refers back to itself, eg struct E<F : F.A> {}.

Author: slavapestov

include/swift/AST/ArchetypeBuilder.h

@@ -218,6 +218,12 @@ class ArchetypeBuilder {
   /// \returns true if an error occurred, false otherwise.
   bool addGenericParameter(GenericTypeParamDecl *GenericParam);
 
+  /// Add the requirements placed on the given abstract type parameter
+  /// to the given potential archetype.
+  ///
+  /// \returns true if an error occurred, false otherwise.
+  bool addGenericParameterRequirements(GenericTypeParamDecl *GenericParam);
+
   /// \brief Add a new generic parameter for which there may be requirements.
   ///
   /// \returns true if an error occurred, false otherwise.

lib/AST/ArchetypeBuilder.cpp

@@ -736,9 +736,13 @@ bool ArchetypeBuilder::addGenericParameter(GenericTypeParamDecl *GenericParam) {
         GenericParam->getDeclaredType()->castTo<GenericTypeParamType>(),
         RootProtocol,
         GenericParam->getName());
-  
-  if (!PA)
-    return true;
+
+  return (!PA);
+}
+
+bool ArchetypeBuilder::addGenericParameterRequirements(GenericTypeParamDecl *GenericParam) {
+  GenericTypeParamKey Key{GenericParam->getDepth(), GenericParam->getIndex()};
+  auto PA = Impl->PotentialArchetypes[Key];
 
   // Add the requirements from the declaration.
   llvm::SmallPtrSet<ProtocolDecl *, 8> visited;

lib/Sema/TypeCheckGeneric.cpp

@@ -257,20 +257,25 @@ bool TypeChecker::checkGenericParamList(ArchetypeBuilder *builder,
     options = TR_GenericSignature;
   }    
 
-  // Visit each of the generic parameters.
+  // First, set the depth of each generic parameter, and add them to the
+  // archetype builder. Do this before checking the inheritance clause,
+  // since it may itself be dependent on one of these parameters.
   unsigned depth = genericParams->getDepth();
   for (auto param : *genericParams) {
-    // Check the generic type parameter.
-    // Set the depth of this type parameter.
     param->setDepth(depth);
 
-    // Check the inheritance clause of this type parameter.
-    checkInheritanceClause(param, resolver);
-
     if (builder) {
-      // Add the generic parameter to the builder.
       if (builder->addGenericParameter(param))
         invalid = true;
+    }
+  }
+
+  // Now, check the inheritance clauses of each parameter.
+  for (auto param : *genericParams) {
+    checkInheritanceClause(param, resolver);
+
+    if (builder) {
+      builder->addGenericParameterRequirements(param);
 
       // Infer requirements from the inherited types.
       for (const auto &inherited : param->getInherited()) {

test/Generics/generic_types.swift

@@ -323,3 +323,12 @@ class X6<T> {
     init(_ value: T2) {}
   }
 }
+
+// Invalid inheritance clause
+
+struct UnsolvableInheritance1<T : T.A> {}
+// expected-error@-1 {{inheritance from non-protocol, non-class type 'T.A'}}
+
+struct UnsolvableInheritance2<T : U.A, U : T.A> {}
+// expected-error@-1 {{inheritance from non-protocol, non-class type 'U.A'}}
+// expected-error@-2 {{inheritance from non-protocol, non-class type 'T.A'}}

validation-test/compiler_crashers/26549-swift-typechecker-resolvetypeincontext.swift renamed to validation-test/compiler_crashers_fixed/26549-swift-typechecker-resolvetypeincontext.swift

@@ -1,4 +1,4 @@
-// RUN: not --crash %target-swift-frontend %s -parse
+// RUN: not %target-swift-frontend %s -parse
 // Distributed under the terms of the MIT license
 // Test case submitted to project by https://github.com/practicalswift (practicalswift)
 // Test case found by fuzzing