[Diagnostics] Use signed integer to store difference in optionality between types

For checked cast coercion warnings let's store difference in optionality
as an `int` because it's possible that "to" type is more optional than
"from" type.

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -7466,7 +7466,7 @@ SourceRange CheckedCastBaseFailure::getCastRange() const {
   llvm_unreachable("There is no other kind of checked cast!");
 }
 
-std::tuple<Type, Type, unsigned>
+std::tuple<Type, Type, int>
 CoercibleOptionalCheckedCastFailure::unwrappedTypes() const {
   SmallVector<Type, 4> fromOptionals;
   SmallVector<Type, 4> toOptionals;
@@ -7483,8 +7483,7 @@ bool CoercibleOptionalCheckedCastFailure::diagnoseIfExpr() const {
     return false;
 
   Type unwrappedFrom, unwrappedTo;
-  unsigned extraFromOptionals;
-  std::tie(unwrappedFrom, unwrappedTo, extraFromOptionals) = unwrappedTypes();
+  std::tie(unwrappedFrom, unwrappedTo, std::ignore) = unwrappedTypes();
 
   SourceRange diagFromRange = getFromRange();
   SourceRange diagToRange = getToRange();
@@ -7515,7 +7514,7 @@ bool CoercibleOptionalCheckedCastFailure::diagnoseForcedCastExpr() const {
   auto fromType = getFromType();
   auto toType = getToType();
   Type unwrappedFrom, unwrappedTo;
-  unsigned extraFromOptionals;
+  int extraFromOptionals;
   std::tie(unwrappedFrom, unwrappedTo, extraFromOptionals) = unwrappedTypes();
 
   SourceRange diagFromRange = getFromRange();
@@ -7558,8 +7557,7 @@ bool CoercibleOptionalCheckedCastFailure::diagnoseConditionalCastExpr() const {
   auto fromType = getFromType();
   auto toType = getToType();
   Type unwrappedFrom, unwrappedTo;
-  unsigned extraFromOptionals;
-  std::tie(unwrappedFrom, unwrappedTo, extraFromOptionals) = unwrappedTypes();
+  std::tie(unwrappedFrom, unwrappedTo, std::ignore) = unwrappedTypes();
 
   SourceRange diagFromRange = getFromRange();
   SourceRange diagToRange = getToRange();

lib/Sema/CSDiagnostics.h

@@ -2496,7 +2496,7 @@ class CoercibleOptionalCheckedCastFailure final
   bool diagnoseAsError() override;
 
 private:
-  std::tuple<Type, Type, unsigned> unwrappedTypes() const;
+  std::tuple<Type, Type, int> unwrappedTypes() const;
 
   bool diagnoseIfExpr() const;