[ConstraintSystem] Add a new conversion - Swift to C pointers

Following pointer conversions are supported in argument positions (when referencing C/ObjC functions):

- Unsafe[Mutable]RawPointer -> Unsafe[Mutable]Pointer<[U]Int>
- Unsafe[Mutable]Pointer<Int{8, 16, ...}> -> Unsafe[Mutable]Pointer<UInt{8, 16, ...}>

Author: xedin

include/swift/Sema/Constraint.h

@@ -269,6 +269,10 @@ enum class ConversionRestrictionKind {
   /// Implicit conversion from a value of CGFloat type to a value of Double type
   /// via an implicit Double initializer call passing a CGFloat value.
   CGFloatToDouble,
+  /// Implicit conversion between Swift and C pointers:
+  //    - Unsafe[Mutable]RawPointer -> Unsafe[Mutable]Pointer<[U]Int>
+  //    - Unsafe[Mutable]Pointer<Int{8, 16, ...}> -> Unsafe[Mutable]Pointer<UInt{8, 16, ...}>
+  PointerToCPointer,
 };
 
 /// Specifies whether a given conversion requires the creation of a temporary

lib/Sema/CSApply.cpp

@@ -6645,7 +6645,8 @@ Expr *ExprRewriter::coerceToType(Expr *expr, Type toType,
       return result;
     }
 
-    case ConversionRestrictionKind::PointerToPointer: {
+    case ConversionRestrictionKind::PointerToPointer:
+    case ConversionRestrictionKind::PointerToCPointer: {
       TypeChecker::requirePointerArgumentIntrinsics(ctx, expr->getLoc());
       Type unwrappedToTy = toType->getOptionalObjectType();
 

lib/Sema/CSDiagnostics.cpp

@@ -6691,6 +6691,7 @@ void NonEphemeralConversionFailure::emitSuggestionNotes() const {
   case ConversionRestrictionKind::ExistentialMetatypeToAnyObject:
   case ConversionRestrictionKind::ProtocolMetatypeToProtocolClass:
   case ConversionRestrictionKind::PointerToPointer:
+  case ConversionRestrictionKind::PointerToCPointer:
   case ConversionRestrictionKind::ArrayUpcast:
   case ConversionRestrictionKind::DictionaryUpcast:
   case ConversionRestrictionKind::SetUpcast:

lib/Sema/CSSimplify.cpp

@@ -11114,7 +11114,11 @@ ConstraintSystem::simplifyRestrictedConstraintImpl(
 
     return matchPointerBaseTypes(ptr1, ptr2);
   }
-    
+
+  case ConversionRestrictionKind::PointerToCPointer: {
+    return SolutionKind::Error; // not yet implemented
+  }
+
   // T < U or T is bridged to V where V < U ===> Array<T> <c Array<U>
   case ConversionRestrictionKind::ArrayUpcast: {
     Type baseType1 = *isArrayType(type1);

lib/Sema/Constraint.cpp

@@ -546,6 +546,8 @@ StringRef swift::constraints::getName(ConversionRestrictionKind kind) {
     return "[inout-to-pointer]";
   case ConversionRestrictionKind::PointerToPointer:
     return "[pointer-to-pointer]";
+  case ConversionRestrictionKind::PointerToCPointer:
+    return "[pointer-to-c-pointer]";
   case ConversionRestrictionKind::ArrayUpcast:
     return "[array-upcast]";
   case ConversionRestrictionKind::DictionaryUpcast:

lib/Sema/ConstraintSystem.cpp

@@ -5129,6 +5129,7 @@ ConstraintSystem::isConversionEphemeral(ConversionRestrictionKind conversion,
   case ConversionRestrictionKind::ExistentialMetatypeToAnyObject:
   case ConversionRestrictionKind::ProtocolMetatypeToProtocolClass:
   case ConversionRestrictionKind::PointerToPointer:
+  case ConversionRestrictionKind::PointerToCPointer:
   case ConversionRestrictionKind::ArrayUpcast:
   case ConversionRestrictionKind::DictionaryUpcast:
   case ConversionRestrictionKind::SetUpcast: