Sema: Add a simpler form of checkGenericArguments()

Author: slavapestov

lib/Sema/TypeCheckGeneric.cpp

@@ -1062,6 +1062,35 @@ CheckGenericArgumentsResult::Kind TypeChecker::checkGenericArguments(
   return CheckGenericArgumentsResult::Success;
 }
 
+CheckGenericArgumentsResult::Kind TypeChecker::checkGenericArguments(
+    ArrayRef<Requirement> requirements) {
+  SmallVector<Requirement, 4> worklist(requirements.begin(), requirements.end());
+
+  bool hadSubstFailure = false;
+
+  while (!worklist.empty()) {
+    auto req = worklist.pop_back_val();
+    switch (req.checkRequirement(worklist, /*allowMissing=*/true)) {
+    case CheckRequirementResult::Success:
+    case CheckRequirementResult::ConditionalConformance:
+    case CheckRequirementResult::PackRequirement:
+      break;
+
+    case CheckRequirementResult::RequirementFailure:
+      return CheckGenericArgumentsResult::RequirementFailure;
+
+    case CheckRequirementResult::SubstitutionFailure:
+      hadSubstFailure = true;
+      break;
+    }
+  }
+
+  if (hadSubstFailure)
+    return CheckGenericArgumentsResult::SubstitutionFailure;
+
+  return CheckGenericArgumentsResult::Success;
+}
+
 Requirement
 RequirementRequest::evaluate(Evaluator &evaluator,
                              WhereClauseOwner owner,

lib/Sema/TypeCheckProtocol.cpp

@@ -5733,9 +5733,7 @@ TypeChecker::conformsToProtocol(Type T, ProtocolDecl *Proto, ModuleDecl *M,
 
   // If we have a conditional requirements that we need to check, do so now.
   if (!condReqs->empty()) {
-    auto conditionalCheckResult = checkGenericArguments(
-        M, *condReqs,
-        [](SubstitutableType *dependentType) { return Type(dependentType); });
+    auto conditionalCheckResult = checkGenericArguments(*condReqs);
     switch (conditionalCheckResult) {
     case CheckGenericArgumentsResult::Success:
       break;

lib/Sema/TypeChecker.h

@@ -535,6 +535,10 @@ checkGenericArguments(ModuleDecl *module, ArrayRef<Requirement> requirements,
                       TypeSubstitutionFn substitutions,
                       SubstOptions options = None);
 
+/// Check the given requirements without applying substitutions.
+CheckGenericArgumentsResult::Kind
+checkGenericArguments(ArrayRef<Requirement> requirements);
+
 /// Checks whether the generic requirements imposed on the nested type
 /// declaration \p decl (if present) are in agreement with the substitutions
 /// that are needed to spell it as a member of the given parent type