[Type checker] Clean up expression type checking flags

lib/Sema/CSDiag.cpp

@@ -394,15 +394,10 @@ Expr *FailureDiagnosis::typeCheckChildIndependently(
   // type check operation.
   Expr *preCheckedExpr = subExpr;
 
-  // Disable structural checks, because we know that the overall expression
-  // has type constraint problems, and we don't want to know about any
-  // syntactic issues in a well-typed subexpression (which might be because
-  // the context is missing).
-  TypeCheckExprOptions TCEOptions = TypeCheckExprFlags::DisableStructuralChecks;
-
   // Make sure that typechecker knows that this is an attempt
   // to diagnose a problem.
-  TCEOptions |= TypeCheckExprFlags::SubExpressionDiagnostics;
+  TypeCheckExprOptions TCEOptions =
+      TypeCheckExprFlags::SubExpressionDiagnostics;
 
   // Claim that the result is discarded to preserve the lvalue type of
   // the expression.

lib/Sema/CSDiagnostics.cpp

@@ -641,7 +641,7 @@ bool GenericArgumentsMismatchFailure::diagnoseAsError() {
     switch (last.getKind()) {
     case ConstraintLocator::ContextualType: {
       auto purpose = getContextualTypePurpose();
-      assert(!(purpose == CTP_Unused && purpose == CTP_CannotFail));
+      assert(!(purpose == CTP_Unused || purpose == CTP_CannotFail));
 
       // If this is call to a closure e.g. `let _: A = { B() }()`
       // let's point diagnostic to its result.

lib/Sema/ConstraintSystem.h

@@ -789,7 +789,7 @@ using OpenedTypeMap =
 
 /// Describes contextual type information about a particular expression
 /// within a constraint system.
-struct ContextualTypeInfo  {
+struct ContextualTypeInfo {
   TypeLoc typeLoc;
   ContextualTypePurpose purpose;
   bool isOpaqueReturnType = false;
@@ -1149,8 +1149,11 @@ class SolutionApplicationTarget {
     struct {
       Expr *expression;
 
+      /// The purpose of the contextual type.
+      ContextualTypePurpose contextualPurpose;
+
       /// The type to which the expression should be converted.
-      Type convertType;
+      TypeLoc convertType;
 
       /// Whether the expression result will be discarded at the end.
       bool isDiscarded;
@@ -1163,9 +1166,18 @@ class SolutionApplicationTarget {
   };
 
 public:
-  SolutionApplicationTarget(Expr *expr, Type convertType, bool isDiscarded) {
+  SolutionApplicationTarget(Expr *expr,
+                            ContextualTypePurpose contextualPurpose,
+                            Type convertType, bool isDiscarded)
+      : SolutionApplicationTarget(expr, contextualPurpose,
+                                  TypeLoc::withoutLoc(convertType),
+                                  isDiscarded) { }
+
+  SolutionApplicationTarget(Expr *expr, ContextualTypePurpose contextualPurpose,
+                            TypeLoc convertType, bool isDiscarded) {
     kind = Kind::expression;
     expression.expression = expr;
+    expression.contextualPurpose = contextualPurpose;
     expression.convertType = convertType;
     expression.isDiscarded = isDiscarded;
   }
@@ -1189,16 +1201,31 @@ class SolutionApplicationTarget {
     }
   }
 
+  ContextualTypePurpose getExprContextualTypePurpose() const {
+    assert(kind == Kind::expression);
+    return expression.contextualPurpose;
+  }
+
   Type getExprConversionType() const {
+    assert(kind == Kind::expression);
+    return expression.convertType.getType();
+  }
+
+  TypeLoc getExprConversionTypeLoc() const {
     assert(kind == Kind::expression);
     return expression.convertType;
   }
 
   void setExprConversionType(Type type) {
+    assert(kind == Kind::expression);
+    expression.convertType = TypeLoc::withoutLoc(type);
+  }
+
+  void setExprConversionTypeLoc(TypeLoc type) {
     assert(kind == Kind::expression);
     expression.convertType = type;
   }
-  
+
   bool isDiscardedExpr() const {
     assert(kind == Kind::expression);
     return expression.isDiscarded;

lib/Sema/TypeCheckConstraints.cpp

@@ -2058,6 +2058,40 @@ bool GenericRequirementsCheckListener::diagnoseUnsatisfiedRequirement(
   return false;
 }
 
+/// Whether the contextual type provided for the given purpose is only a
+/// hint, and not a requirement.
+static bool contextualTypeIsOnlyAHint(ContextualTypePurpose ctp,
+                                      TypeCheckExprOptions options) {
+  switch (ctp) {
+  case CTP_Initialization:
+    return !options.contains(
+        TypeCheckExprFlags::ConvertTypeIsOpaqueReturnType);
+  case CTP_ForEachStmt:
+    return true;
+  case CTP_Unused:
+  case CTP_ReturnStmt:
+  case CTP_ReturnSingleExpr:
+  case CTP_YieldByValue:
+  case CTP_YieldByReference:
+  case CTP_ThrowStmt:
+  case CTP_EnumCaseRawValue:
+  case CTP_DefaultParameter:
+  case CTP_AutoclosureDefaultParameter:
+  case CTP_CalleeResult:
+  case CTP_CallArgument:
+  case CTP_ClosureResult:
+  case CTP_ArrayElement:
+  case CTP_DictionaryKey:
+  case CTP_DictionaryValue:
+  case CTP_CoerceOperand:
+  case CTP_AssignSource:
+  case CTP_SubscriptAssignSource:
+  case CTP_Condition:
+  case CTP_CannotFail:
+    return false;
+  }
+}
+
 #pragma mark High-level entry points
 Type TypeChecker::typeCheckExpression(Expr *&expr, DeclContext *dc,
                                       TypeLoc convertType,
@@ -2128,7 +2162,7 @@ Type TypeChecker::typeCheckExpression(Expr *&expr, DeclContext *dc,
 
   // If the convertType is *only* provided for that hint, then null it out so
   // that we don't later treat it as an actual conversion constraint.
-  if (options.contains(TypeCheckExprFlags::ConvertTypeIsOnlyAHint))
+  if (contextualTypeIsOnlyAHint(convertTypePurpose, options))
     convertType = TypeLoc();
 
   // If the client can handle unresolved type variables, leave them in the
@@ -2149,7 +2183,7 @@ Type TypeChecker::typeCheckExpression(Expr *&expr, DeclContext *dc,
 
   // Attempt to solve the constraint system.
   SolutionApplicationTarget target(
-      expr, convertTo,
+      expr, convertTypePurpose, convertTo,
       options.contains(TypeCheckExprFlags::IsDiscarded));
   auto viable = cs.solve(target, listener, allowFreeTypeVariables);
   if (!viable)
@@ -2206,7 +2240,7 @@ Type TypeChecker::typeCheckExpression(Expr *&expr, DeclContext *dc,
   // Unless the client has disabled them, perform syntactic checks on the
   // expression now.
   if (!cs.shouldSuppressDiagnostics() &&
-      !options.contains(TypeCheckExprFlags::DisableStructuralChecks)) {
+      !options.contains(TypeCheckExprFlags::SubExpressionDiagnostics)) {
     bool isExprStmt = options.contains(TypeCheckExprFlags::IsExprStmt);
     performSyntacticExprDiagnostics(result, dc, isExprStmt);
   }
@@ -2249,7 +2283,8 @@ getTypeOfExpressionWithoutApplying(Expr *&expr, DeclContext *dc,
   // re-check.
   if (needClearType)
     expr->setType(Type());
-  SolutionApplicationTarget target(expr, Type(), /*isDiscarded=*/false);
+  SolutionApplicationTarget target(
+      expr, CTP_Unused, Type(), /*isDiscarded=*/false);
   auto viable = cs.solve(target, listener, allowFreeTypeVariables);
   if (!viable) {
     recoverOriginalType();
@@ -2329,7 +2364,8 @@ void TypeChecker::getPossibleTypesOfExpressionWithoutApplying(
   if (originalType && originalType->hasError())
     expr->setType(Type());
 
-  SolutionApplicationTarget target(expr, Type(), /*isDiscarded=*/false);
+  SolutionApplicationTarget target(
+      expr, CTP_Unused, Type(), /*isDiscarded=*/false);
   if (auto viable = cs.solve(target, listener, allowFreeTypeVariables)) {
     expr = target.getAsExpr();
     for (auto &solution : *viable) {
@@ -2655,7 +2691,7 @@ bool TypeChecker::typeCheckBinding(Pattern *&pattern, Expr *&initializer,
 
   TypeLoc contextualType;
   auto contextualPurpose = CTP_Unused;
-  TypeCheckExprOptions flags = TypeCheckExprFlags::ConvertTypeIsOnlyAHint;
+  TypeCheckExprOptions flags = None;
 
   // Set the contextual purpose even if the pattern doesn't have a type so
   // if there's an error we can use that information to inform diagnostics.
@@ -2674,7 +2710,6 @@ bool TypeChecker::typeCheckBinding(Pattern *&pattern, Expr *&initializer,
     // opaque type.
     if (auto opaqueType = patternType->getAs<OpaqueTypeArchetypeType>()){
       flags |= TypeCheckExprFlags::ConvertTypeIsOpaqueReturnType;
-      flags -= TypeCheckExprFlags::ConvertTypeIsOnlyAHint;
     }
 
     // Only provide a TypeLoc if it makes sense to allow diagnostics.
@@ -3042,7 +3077,7 @@ bool TypeChecker::typeCheckForEachBinding(DeclContext *dc, ForEachStmt *stmt) {
   // Type-check the for-each loop sequence and element pattern.
   auto resultTy = TypeChecker::typeCheckExpression(
       seq, dc, TypeLoc::withoutLoc(sequenceProto->getDeclaredType()),
-      CTP_ForEachStmt, TypeCheckExprFlags::ConvertTypeIsOnlyAHint, &listener);
+      CTP_ForEachStmt, None, &listener);
   if (!resultTy)
     return true;
   return false;

lib/Sema/TypeChecker.h

@@ -163,31 +163,18 @@ enum class TypeCheckExprFlags {
   /// disables constraints forcing an lvalue result to be loadable.
   IsDiscarded = 0x01,
 
-  /// Whether the client wants to disable the structural syntactic restrictions
-  /// that we force for style or other reasons.
-  DisableStructuralChecks = 0x02,
-
   /// If set, the client wants a best-effort solution to the constraint system,
   /// but can tolerate a solution where all of the constraints are solved, but
   /// not all type variables have been determined.  In this case, the constraint
   /// system is not applied to the expression AST, but the ConstraintSystem is
   /// left in-tact.
   AllowUnresolvedTypeVariables = 0x08,
 
-  /// If set, the 'convertType' specified to typeCheckExpression should not
-  /// produce a conversion constraint, but it should be used to guide the
-  /// solution in terms of performance optimizations of the solver, and in terms
-  /// of guiding diagnostics.
-  ConvertTypeIsOnlyAHint = 0x10,
-
   /// If set, this expression isn't embedded in a larger expression or
   /// statement. This should only be used for syntactic restrictions, and should
   /// not affect type checking itself.
   IsExprStmt = 0x20,
 
-  /// This is an inout yield.
-  IsInOutYield = 0x100,
-
   /// If set, a conversion constraint should be specified so that the result of
   /// the expression is an optional type.
   ExpressionTypeMustBeOptional = 0x200,
@@ -821,11 +808,9 @@ class TypeChecker final {
   /// to be possible.
   ///
   /// \param convertType The type that the expression is being converted to,
-  /// or null if the expression is standalone.  If the 'ConvertTypeIsOnlyAHint'
-  /// option is specified, then this is only a hint, it doesn't produce a full
-  /// conversion constraint. The location information is only used for
-  /// diagnostics should the conversion fail; it is safe to pass a TypeLoc
-  /// without location information.
+  /// or null if the expression is standalone. The location information is
+  /// only used for diagnostics should the conversion fail; it is safe to pass
+  /// a TypeLoc without location information.
   ///
   /// \param options Options that control how type checking is performed.
   ///
@@ -847,12 +832,6 @@ class TypeChecker final {
                       ExprTypeCheckListener *listener = nullptr,
                       constraints::ConstraintSystem *baseCS = nullptr);
 
-  static Type typeCheckExpression(Expr *&expr, DeclContext *dc,
-                                  ExprTypeCheckListener *listener) {
-    return TypeChecker::typeCheckExpression(expr, dc, TypeLoc(), CTP_Unused,
-                                            TypeCheckExprOptions(), listener);
-  }
-
   /// Type check the given expression and return its type without
   /// applying the solution.
   ///