Revert "Sema: Change associated type inference handling of generic parameters"

This reverts commit fe7631c.

Author: slavapestov

lib/Sema/AssociatedTypeInference.cpp

@@ -980,6 +980,7 @@ class AssociatedTypeInference {
 
   /// Infer associated type witnesses for the given associated type.
   InferredAssociatedTypesByWitnesses inferTypeWitnessesViaAssociatedType(
+                   const llvm::SetVector<AssociatedTypeDecl *> &allUnresolved,
                    AssociatedTypeDecl *assocType);
 
   /// Infer associated type witnesses for all relevant value requirements.
@@ -1678,7 +1679,8 @@ AssociatedTypeInference::inferTypeWitnessesViaValueWitnesses(
       if (assocTypes.count(assocType) == 0)
         continue;
 
-      auto reqInferred = inferTypeWitnessesViaAssociatedType(assocType);
+      auto reqInferred = inferTypeWitnessesViaAssociatedType(assocTypes,
+                                                             assocType);
       if (!reqInferred.empty())
         result.push_back({req, std::move(reqInferred)});
 
@@ -1826,12 +1828,10 @@ static Type removeSelfParam(ValueDecl *value, Type type) {
 
 InferredAssociatedTypesByWitnesses
 AssociatedTypeInference::inferTypeWitnessesViaAssociatedType(
+                   const llvm::SetVector<AssociatedTypeDecl *> &allUnresolved,
                    AssociatedTypeDecl *assocType) {
   InferredAssociatedTypesByWitnesses result;
 
-  LLVM_DEBUG(llvm::dbgs() << "Considering associated type:\n";
-             assocType->dump(llvm::dbgs()));
-
   // Check if this associated type is actually fixed to a fully concrete type by
   // a same-type requirement in a protocol that our conforming type conforms to.
   //
@@ -1856,34 +1856,6 @@ AssociatedTypeInference::inferTypeWitnessesViaAssociatedType(
     }
   }
 
-  // Look for a generic parameter with the same name as this associated type.
-  if (ctx.LangOpts.EnableExperimentalAssociatedTypeInference) {
-    // Ignore the generic parameters for AsyncIteratorProtocol.Failure and
-    // AsyncSequence.Failure.
-    if (!isAsyncIteratorProtocolFailure(assocType)) {
-      if (auto genericSig = dc->getGenericSignatureOfContext()) {
-        for (auto *gp : genericSig.getInnermostGenericParams()) {
-          // Packs cannot witness associated type requirements.
-          if (gp->isParameterPack())
-            continue;
-
-          if (gp->getName() == assocType->getName()) {
-            auto witnessType = dc->mapTypeIntoContext(gp);
-
-            // Add this result.
-            InferredAssociatedTypesByWitness inferred;
-            inferred.Witness = gp->getDecl();
-            inferred.Inferred.push_back({assocType, witnessType});
-            result.push_back(std::move(inferred));
-
-            LLVM_DEBUG(llvm::dbgs() << "Candidate generic parameter:\n";
-                       gp->dump(llvm::dbgs()));
-          }
-        }
-      }
-    }
-  }
-
   // Form the default name _Default_Foo.
   DeclNameRef defaultName;
   {
@@ -2468,6 +2440,29 @@ AssociatedTypeInference::computeAbstractTypeWitness(
 void AssociatedTypeInference::collectAbstractTypeWitnesses(
     TypeWitnessSystem &system,
     ArrayRef<AssociatedTypeDecl *> unresolvedAssocTypes) const {
+  // Look for suitably-named generic parameters first, before we go digging
+  // through same-type requirements of protocols.
+  if (auto genericSig = dc->getGenericSignatureOfContext()) {
+    for (auto *const assocType : unresolvedAssocTypes) {
+      // Ignore the generic parameters for AsyncIteratorProtocol.Failure and
+      // AsyncSequence.Failure.
+      if (isAsyncIteratorProtocolFailure(assocType))
+        continue;
+
+      for (auto *gp : genericSig.getInnermostGenericParams()) {
+        // Packs cannot witness associated type requirements.
+        if (gp->isParameterPack())
+          continue;
+
+        if (gp->getName() == assocType->getName()) {
+          system.addTypeWitness(assocType->getName(),
+                                dc->mapTypeIntoContext(gp),
+                                /*preferred=*/true);
+        }
+      }
+    }
+  }
+
   auto considerProtocolRequirements = [&](ProtocolDecl *conformedProto) {
     // FIXME: The RequirementMachine will assert on re-entrant construction.
     // We should find a more principled way of breaking this cycle.