[4.0] [QoI] Improve contextual error diagnostics related to calls

lib/Sema/CSDiag.cpp

@@ -2066,12 +2066,17 @@ class FailureDiagnosis :public ASTVisitor<FailureDiagnosis, /*exprresult*/bool>{
 
   /// Attempt to produce a diagnostic for a mismatch between an expression's
   /// type and its assumed contextual type.
-  bool diagnoseContextualConversionError();
+  bool diagnoseContextualConversionError(Expr *expr, Type contextualType);
 
   /// For an expression being type checked with a CTP_CalleeResult contextual
   /// type, try to diagnose a problem.
   bool diagnoseCalleeResultContextualConversionError();
 
+  /// Attempt to produce a diagnostic for a mismatch between a call's
+  /// type and its assumed contextual type.
+  bool diagnoseCallContextualConversionErrors(ApplyExpr *callEpxr,
+                                              Type contextualType);
+
 private:
   /// Validate potential contextual type for type-checking one of the
   /// sub-expressions, usually correct/valid types are the ones which
@@ -3863,10 +3868,10 @@ static bool tryDiagnoseNonEscapingParameterToEscaping(Expr *expr, Type srcType,
   return true;
 }
 
-bool FailureDiagnosis::diagnoseContextualConversionError() {
+bool FailureDiagnosis::diagnoseContextualConversionError(Expr *expr,
+                                                         Type contextualType) {
   // If the constraint system has a contextual type, then we can test to see if
   // this is the problem that prevents us from solving the system.
-  Type contextualType = CS->getContextualType();
   if (!contextualType) {
     // This contextual conversion constraint doesn't install an actual type.
     if (CS->getContextualTypePurpose() == CTP_CalleeResult)
@@ -6066,7 +6071,7 @@ bool FailureDiagnosis::diagnoseTrailingClosureErrors(ApplyExpr *callExpr) {
     // related to function type, let's try to diagnose it.
     if (possibleTypes.empty() && contextualType &&
         !contextualType->hasUnresolvedType())
-      return diagnoseContextualConversionError();
+      return diagnoseContextualConversionError(callExpr, contextualType);
 
     auto currentType = fnExpr->getType();
     if (currentType && currentType->is<ErrorType>())
@@ -6166,6 +6171,49 @@ bool FailureDiagnosis::diagnoseTrailingClosureErrors(ApplyExpr *callExpr) {
   return false;
 }
 
+/// Check if there failure associated with expresssion is related
+/// to given contextual type.
+bool FailureDiagnosis::diagnoseCallContextualConversionErrors(
+    ApplyExpr *callExpr, Type contextualType) {
+  if (!contextualType || contextualType->hasUnresolvedType())
+    return false;
+
+  auto &TC = CS->TC;
+  auto *DC = CS->DC;
+
+  auto typeCheckExpr = [](TypeChecker &TC, Expr *expr, DeclContext *DC,
+                          SmallVectorImpl<Type> &types,
+                          Type contextualType = Type()) {
+    CalleeListener listener(contextualType);
+    TC.getPossibleTypesOfExpressionWithoutApplying(
+        expr, DC, types, FreeTypeVariableBinding::Disallow, &listener);
+  };
+
+  // First let's type-check expression without contextual type, and
+  // see if that's going to produce a type, if so, let's type-check
+  // again, this time using given contextual type.
+  SmallVector<Type, 4> withoutContextual;
+  typeCheckExpr(TC, callExpr, DC, withoutContextual);
+
+  // If there are no types returned, it means that problem was
+  // nothing to do with contextual information, probably parameter/argument
+  // mismatch.
+  if (withoutContextual.empty())
+    return false;
+
+  SmallVector<Type, 4> withContextual;
+  typeCheckExpr(TC, callExpr, DC, withContextual, contextualType);
+  // If type-checking with contextual type didn't produce any results
+  // it means that we have a contextual mismatch.
+  if (withContextual.empty())
+    return diagnoseContextualConversionError(callExpr, contextualType);
+
+  // If call produces a single type when type-checked with contextual
+  // expression, it means that the problem is elsewhere, any other
+  // outcome is ambiguous.
+  return false;
+}
+
 bool FailureDiagnosis::visitApplyExpr(ApplyExpr *callExpr) {
   // If this call involves trailing closure as an argument,
   // let's treat it specially, because re-typecheck of the
@@ -6174,6 +6222,9 @@ bool FailureDiagnosis::visitApplyExpr(ApplyExpr *callExpr) {
   if (diagnoseTrailingClosureErrors(callExpr))
     return true;
 
+  if (diagnoseCallContextualConversionErrors(callExpr, CS->getContextualType()))
+    return true;
+
   // Type check the function subexpression to resolve a type for it if
   // possible.
   auto fnExpr = typeCheckChildIndependently(callExpr->getFn());
@@ -8518,7 +8569,7 @@ void ConstraintSystem::diagnoseFailureForExpr(Expr *expr) {
     return;
 
   // If this is a contextual conversion problem, dig out some information.
-  if (diagnosis.diagnoseContextualConversionError())
+  if (diagnosis.diagnoseContextualConversionError(expr, getContextualType()))
     return;
 
   // If we can diagnose a problem based on the constraints left laying around in

lib/Sema/TypeCheckConstraints.cpp

@@ -1980,40 +1980,37 @@ void TypeChecker::getPossibleTypesOfExpressionWithoutApplying(
     ExprTypeCheckListener *listener) {
   PrettyStackTraceExpr stackTrace(Context, "type-checking", expr);
 
+  ExprCleaner cleaner(expr);
+
   // Construct a constraint system from this expression.
   ConstraintSystemOptions options;
   options |= ConstraintSystemFlags::AllowFixes;
   options |= ConstraintSystemFlags::ReturnAllDiscoveredSolutions;
 
   ConstraintSystem cs(*this, dc, options);
-  CleanupIllFormedExpressionRAII cleanup(Context, expr);
 
   // Attempt to solve the constraint system.
   SmallVector<Solution, 4> viable;
-  const Type originalType = expr->getType();
-  const bool needClearType = originalType && originalType->hasError();
-  const auto recoverOriginalType = [&]() {
-    if (needClearType)
-      expr->setType(originalType);
-  };
 
   // If the previous checking gives the expr error type,
   // clear the result and re-check.
-  if (needClearType)
-    expr->setType(Type());
+  {
+    CleanupIllFormedExpressionRAII cleanup(Context, expr);
 
-  solveForExpression(expr, dc, /*convertType*/ Type(), allowFreeTypeVariables,
-                     listener, cs, viable,
-                     TypeCheckExprFlags::SuppressDiagnostics);
+    const Type originalType = expr->getType();
+    if (originalType && originalType->hasError())
+      expr->setType(Type());
+
+    solveForExpression(expr, dc, /*convertType*/ Type(), allowFreeTypeVariables,
+                       listener, cs, viable,
+                       TypeCheckExprFlags::SuppressDiagnostics);
+  }
 
   for (auto &solution : viable) {
     auto exprType = solution.simplifyType(cs.getType(expr));
     assert(exprType && !exprType->hasTypeVariable());
     types.push_back(exprType);
   }
-
-  // Recover the original type if needed.
-  recoverOriginalType();
 }
 
 bool TypeChecker::typeCheckCompletionSequence(Expr *&expr, DeclContext *DC) {

test/Constraints/array_literal.swift

@@ -50,7 +50,7 @@ useDoubleList([1.0,2,3])
 useDoubleList([1.0,2.0,3.0])
 
 useIntDict(["Niners" => 31, "Ravens" => 34])
-useIntDict(["Niners" => 31, "Ravens" => 34.0]) // expected-error{{cannot convert value of type 'Double' to expected argument type 'Int'}}
+useIntDict(["Niners" => 31, "Ravens" => 34.0]) // expected-error{{cannot convert value of type '(String, Double)' to expected element type '(String, Int)'}}
 // <rdar://problem/22333090> QoI: Propagate contextual information in a call to operands
 useDoubleDict(["Niners" => 31, "Ravens" => 34.0])
 useDoubleDict(["Niners" => 31.0, "Ravens" => 34])

test/Constraints/diagnostics.swift

@@ -997,3 +997,30 @@ func rdar32726044() -> Float {
   return f
 }
 
+// SR-5045 - Attempting to return result of reduce(_:_:) in a method with no return produces ambiguous error
+func sr5045() {
+  let doubles: [Double] = [1, 2, 3]
+  return doubles.reduce(0, +)
+  // expected-error@-1 {{unexpected non-void return value in void function}}
+}
+
+// rdar://problem/32934129 - QoI: misleading diagnostic
+class L_32934129<T : Comparable> {
+  init(_ value: T) { self.value = value }
+  init(_ value: T, _ next: L_32934129<T>?) {
+    self.value = value
+    self.next = next
+  }
+
+  var value: T
+  var next: L_32934129<T>? = nil
+
+  func length() -> Int {
+    func inner(_ list: L_32934129<T>?, _ count: Int) {
+    guard let list = list else { return count } // expected-error {{unexpected non-void return value in void function}}
+      return inner(list.next, count + 1)
+    }
+
+    return inner(self, 0) // expected-error {{cannot convert return expression of type '()' to return type 'Int'}}
+  }
+}

test/Constraints/fixes.swift

@@ -143,4 +143,4 @@ struct S1116 {
 }
 
 let a1116: [S1116] = []
-var s1116 = Set(1...10).subtracting(a1116.map({ $0.s })) // expected-error {{'map' produces '[T]', not the expected contextual result type 'Set<Int>'}}
+var s1116 = Set(1...10).subtracting(a1116.map({ $0.s })) // expected-error {{cannot convert value of type '[Int?]' to expected argument type 'Set<Int>'}}

test/Generics/deduction.swift

@@ -22,7 +22,7 @@ func useIdentity(_ x: Int, y: Float, i32: Int32) {
 
   // Deduction where the result type and input type can get different results
   var xx : X, yy : Y
-  xx = identity(yy) // expected-error{{cannot convert value of type 'Y' to expected argument type 'X'}}
+  xx = identity(yy) // expected-error{{cannot assign value of type 'Y' to type 'X'}}
   xx = identity2(yy) // expected-error{{cannot convert value of type 'Y' to expected argument type 'X'}}
 }
 

test/Serialization/Recovery/typedefs.swift

@@ -38,11 +38,11 @@ public func testVTableBuilding(user: User) {
 } // CHECK-IR: ret void
 
 #if VERIFY
-let _: String = useAssoc(ImportedType.self) // expected-error {{cannot convert call result type '_.Assoc?' to expected type 'String'}}
+let _: String = useAssoc(ImportedType.self) // expected-error {{cannot convert value of type 'Int32?' to specified type 'String'}}
 let _: Bool? = useAssoc(ImportedType.self) // expected-error {{cannot convert value of type 'Int32?' to specified type 'Bool?'}}
 let _: Int32? = useAssoc(ImportedType.self)
 
-let _: String = useAssoc(AnotherType.self) // expected-error {{cannot convert call result type '_.Assoc?' to expected type 'String'}}
+let _: String = useAssoc(AnotherType.self) // expected-error {{cannot convert value of type 'AnotherType.Assoc?' (aka 'Optional<Int32>') to specified type 'String'}}
 let _: Bool? = useAssoc(AnotherType.self) // expected-error {{cannot convert value of type 'AnotherType.Assoc?' (aka 'Optional<Int32>') to specified type 'Bool?'}}
 let _: Int32? = useAssoc(AnotherType.self)