[ConstraintSystem] Add a new contextual type purpose - expression pattern

This makes it possible to associate expression with its parent pattern.

Author: xedin

include/swift/Sema/ConstraintLocator.h

@@ -85,6 +85,9 @@ enum ContextualTypePurpose : uint8_t {
   CTP_ComposedPropertyWrapper, ///< Composed wrapper type expected to match
                                ///< former 'wrappedValue' type
 
+  CTP_ExprPattern,      ///< `~=` operator application associated with expression
+                        /// pattern.
+
   CTP_CannotFail,       ///< Conversion can never fail. abort() if it does.
 };
 

lib/Sema/CSApply.cpp

@@ -8936,6 +8936,7 @@ ExprWalker::rewriteTarget(SolutionApplicationTarget target) {
     case CTP_Unused:
     case CTP_CaseStmt:
     case CTP_ReturnStmt:
+    case CTP_ExprPattern:
     case swift::CTP_ReturnSingleExpr:
     case swift::CTP_YieldByValue:
     case swift::CTP_YieldByReference:

lib/Sema/CSDiagnostics.cpp

@@ -705,6 +705,7 @@ Optional<Diag<Type, Type>> GenericArgumentsMismatchFailure::getDiagnosticFor(
   case CTP_YieldByReference:
   case CTP_CalleeResult:
   case CTP_EnumCaseRawValue:
+  case CTP_ExprPattern:
     break;
   }
   return None;
@@ -2533,6 +2534,7 @@ getContextualNilDiagnostic(ContextualTypePurpose CTP) {
   case CTP_YieldByReference:
   case CTP_WrappedProperty:
   case CTP_ComposedPropertyWrapper:
+  case CTP_ExprPattern:
     return None;
 
   case CTP_EnumCaseRawValue:
@@ -3296,6 +3298,7 @@ ContextualFailure::getDiagnosticFor(ContextualTypePurpose context,
   case CTP_CannotFail:
   case CTP_YieldByReference:
   case CTP_CalleeResult:
+  case CTP_ExprPattern:
     break;
   }
   return None;

lib/Sema/CSSimplify.cpp

@@ -12944,6 +12944,7 @@ void ConstraintSystem::addContextualConversionConstraint(
   case CTP_ForEachStmt:
   case CTP_WrappedProperty:
   case CTP_ComposedPropertyWrapper:
+  case CTP_ExprPattern:
     break;
   }
 

lib/Sema/ConstraintSystem.cpp

@@ -5873,6 +5873,7 @@ bool SolutionApplicationTarget::contextualTypeIsOnlyAHint() const {
   case CTP_WrappedProperty:
   case CTP_ComposedPropertyWrapper:
   case CTP_CannotFail:
+  case CTP_ExprPattern:
     return false;
   }
   llvm_unreachable("invalid contextual type");