Sema: Move some code from canPossiblyConvertTo() to isLikelyExactMatch()

Author: slavapestov

include/swift/Sema/Subtyping.h

@@ -61,16 +61,15 @@ bool hasConversions(Type type);
 enum ConflictFlag : unsigned {
   Category = 1 << 0,
   Exact = 1 << 1,
-  Nominal = 1 << 2,
-  Class = 1 << 3,
-  Structural = 1 << 4,
-  Array = 1 << 5,
-  Dictionary = 1 << 6,
-  Set = 1 << 7,
-  Optional = 1 << 8,
-  Double = 1 << 9,
-  Conformance = 1 << 10,
-  Mutability = 1 << 11
+  Class = 1 << 2,
+  Structural = 1 << 3,
+  Array = 1 << 4,
+  Dictionary = 1 << 5,
+  Set = 1 << 6,
+  Optional = 1 << 7,
+  Double = 1 << 8,
+  Conformance = 1 << 9,
+  Mutability = 1 << 10
 };
 using ConflictReason = OptionSet<ConflictFlag>;
 

lib/Sema/CSLookahead.cpp

@@ -230,8 +230,6 @@ static void pruneDisjunctionImpl(
             llvm::errs() << " category";
           if (reason.contains(ConflictFlag::Exact))
             llvm::errs() << " exact";
-          if (reason.contains(ConflictFlag::Nominal))
-            llvm::errs() << " nominal";
           if (reason.contains(ConflictFlag::Class))
             llvm::errs() << " class";
           if (reason.contains(ConflictFlag::Structural))

lib/Sema/Subtyping.cpp

@@ -30,12 +30,18 @@ using namespace swift;
 using namespace constraints;
 
 std::optional<bool>
-swift::constraints::isLikelyExactMatch(Type first, Type second) {
-  if (auto *firstDecl = first->getAnyNominal()) {
+swift::constraints::isLikelyExactMatch(Type lhs, Type rhs) {
+  if (!lhs->hasTypeVariable() && !lhs->hasTypeParameter() &&
+      !rhs->hasTypeVariable() && !rhs->hasTypeParameter()) {
+    return lhs->isEqual(rhs);
+  }
+
+  if (auto *lhsDecl = lhs->getAnyNominal()) {
     // FIXME: Make this more precise.
-    auto *secondDecl = second->getAnyNominal();
-    return firstDecl == secondDecl;
+    auto *rhsDecl = rhs->getAnyNominal();
+    return lhsDecl == rhsDecl;
   }
+
   // FIXME: Handle other type kinds.
   return std::nullopt;
 }
@@ -139,15 +145,9 @@ ConflictReason swift::constraints::canPossiblyConvertTo(
   if (lhsKind == rhsKind) {
     switch (lhsKind) {
     case ConversionBehavior::None: {
-      if (!lhs->hasTypeVariable() && !lhs->hasTypeParameter() &&
-          !rhs->hasTypeVariable() && !rhs->hasTypeParameter()) {
-        if (!lhs->isEqual(rhs))
-          return ConflictFlag::Exact;
-      }
-
       auto result = isLikelyExactMatch(lhs, rhs);
       if (result.has_value() && !*result)
-        return ConflictFlag::Nominal;
+        return ConflictFlag::Exact;
 
       break;
     }