Rework assignment diagnostics to be built in terms of contextual types,

where we type check the destination first, then apply its type to the source.

This allows us to get diagnostics for assignments that are as good as PBD
initializers and other cases.


Swift SVN r31404

Author: lattner

include/swift/AST/DiagnosticsSema.def

@@ -150,11 +150,6 @@ ERROR(cannot_subscript_base,sema,none,
       "cannot subscript a value of type %0",
       (Type))
 
-
-ERROR(cannot_assign_values,sema,none,
-      "cannot assign a value of type %0 to a value of type %1",
-      (Type, Type))
-
 ERROR(cannot_pass_rvalue_inout_subelement,sema_tcs,none,
       "cannot pass immutable value as inout argument: %0",
       (StringRef))
@@ -297,6 +292,15 @@ ERROR(cannot_convert_coerce_protocol,sema_tcd,none,
 ERROR(cannot_convert_coerce_nil,sema,none,
       "nil is not compatible with type %0 in coercion", (Type))
 
+// Assign Expr
+ERROR(cannot_convert_assign,sema,none,
+      "cannot assign value of type %0 to type %1",
+      (Type,Type))
+ERROR(cannot_convert_assign_protocol,sema_tcd,none,
+      "value of type %0 does not conform to %1 in assignment",
+      (Type, Type))
+ERROR(cannot_convert_assign_nil,sema,none,
+      "nil cannot be assigned to type %0", (Type))
 
 
 ERROR(throws_functiontype_mismatch,sema_tcc,none,

lib/Sema/CSDiag.cpp

@@ -2975,6 +2975,11 @@ bool FailureDiagnosis::diagnoseContextualConversionError() {
     diagIDProtocol = diag::cannot_convert_coerce_protocol;
     nilDiag = diag::cannot_convert_coerce_nil;
     break;
+  case CTP_AssignSource:
+    diagID = diag::cannot_convert_assign;
+    diagIDProtocol = diag::cannot_convert_assign_protocol;
+    nilDiag = diag::cannot_convert_assign_nil;
+    break;
   }
 
   // If we're diagnostic an issue with 'nil', produce a specific diagnostic,
@@ -3554,34 +3559,25 @@ bool FailureDiagnosis::visitAssignExpr(AssignExpr *assignExpr) {
     return true;
   }
 
-  // FIXME: Should check dest expr first, then contextually convert the source
-  // to it.
-  
-  // If the source type is already an error type, we've already posted an error.
-  auto srcExpr = typeCheckChildIndependently(assignExpr->getSrc());
-  if (!srcExpr) return true;
-
+  // Type check the destination first, so we can coerce the source to it.
   auto destExpr = typeCheckChildIndependently(assignExpr->getDest(),
                                               TCC_AllowLValue);
   if (!destExpr) return true;
 
-  auto destType = destExpr->getType();
-  auto srcType = srcExpr->getType();
-
   // If the result type is a non-lvalue, then we are failing because it is
   // immutable and that's not a great thing to assign to.
+  auto destType = destExpr->getType();
   if (!destType->isLValueType()) {
     CS->diagnoseAssignmentFailure(destExpr, destType, assignExpr->getLoc());
     return true;
   }
 
-  // If the two types are ok, it must be a contextual problem.
-  if (srcType->isEqual(destType->getRValueType()))
-    return false;
-
-  diagnose(srcExpr->getLoc(), diag::cannot_assign_values, srcType,
-           destType->getRValueType());
-  return true;
+  // If the source type is already an error type, we've already posted an error.
+  auto srcExpr = typeCheckChildIndependently(assignExpr->getSrc(),
+                                     destType->getLValueOrInOutObjectType(),
+                                             CTP_AssignSource);
+  if (!srcExpr) return true;
+  return false;
 }
 
 bool FailureDiagnosis::visitInOutExpr(InOutExpr *IOE) {

lib/Sema/TypeChecker.h

@@ -155,6 +155,7 @@ enum ContextualTypePurpose {
   CTP_DictionaryKey,    ///< DictionaryExpr keys should have a specific type.
   CTP_DictionaryValue,  ///< DictionaryExpr values should have a specific type.
   CTP_CoerceOperand,    ///< CoerceExpr operand coerced to specific type.
+  CTP_AssignSource,     ///< AssignExpr source operand coerced to result type.
 
   CTP_CannotFail,       ///< Conversion can never fail. abort() if it does.
 };

test/ClangModules/ctypes_parse.swift

@@ -256,7 +256,7 @@ func testFunctionPointers() {
     = getFunctionPointer2()
 
   useFunctionPointer2(anotherFP)
-  anotherFP = fp // expected-error {{cannot assign a value of type 'fptr!' to a value of type '@convention(c) (CInt, CLong, UnsafeMutablePointer<Void>) -> Void'}}
+  anotherFP = fp // expected-error {{cannot assign value of type 'fptr!' to type '@convention(c) (CInt, CLong, UnsafeMutablePointer<Void>) -> Void'}}
 }
 
 func testStructDefaultInit() {

test/ClangModules/objc_parse.swift

@@ -193,7 +193,7 @@ func testProtocols(b: B, bp: BProto) {
   var c1 : Cat1Proto = b
   var bcat1 = b.getAsProtoWithCat()
   c1 = bcat1
-  bcat1 = c1 // expected-error{{cannot assign a value of type 'Cat1Proto' to a value of type 'protocol<BProto, Cat1Proto>!'}}
+  bcat1 = c1 // expected-error{{cannot assign value of type 'Cat1Proto' to type 'protocol<BProto, Cat1Proto>!'}}
 }
 
 // Methods only defined in a protocol

test/Constraints/assignment.swift

@@ -40,7 +40,7 @@ i = j
 _ = (i, f)
 slice[7] = i
 
-slice[7] = f // expected-error{{cannot assign a value of type 'Y' to a value of type 'X'}}
+slice[7] = f // expected-error{{cannot assign value of type 'Y' to type 'X'}}
 
 slice[7] = _ // expected-error{{'_' can only appear in a pattern or on the left side of an assignment}}
 

test/Constraints/bridging.swift

@@ -82,7 +82,7 @@ func arrayToNSArray() {
   nsa = [BridgedClass]()
   nsa = [OtherClass]()
   nsa = [BridgedStruct]()
-  nsa = [NotBridgedStruct]() // expected-error{{cannot assign a value of type '[NotBridgedStruct]' to a value of type 'NSArray'}}
+  nsa = [NotBridgedStruct]() // expected-error{{cannot assign value of type '[NotBridgedStruct]' to type 'NSArray'}}
 
   nsa = [AnyObject]() as NSArray
   nsa = [BridgedClass]() as NSArray
@@ -124,12 +124,12 @@ func dictionaryToNSDictionary() {
   nsd = [NSObject : OtherClass]() as NSDictionary
   nsd = [NSObject : BridgedStruct]()
   nsd = [NSObject : BridgedStruct]() as NSDictionary
-  nsd = [NSObject : NotBridgedStruct]() // expected-error{{cannot assign a value of type '[NSObject : NotBridgedStruct]' to a value of type 'NSDictionary'}}
+  nsd = [NSObject : NotBridgedStruct]() // expected-error{{cannot assign value of type '[NSObject : NotBridgedStruct]' to type 'NSDictionary'}}
   nsd = [NSObject : NotBridgedStruct]() as NSDictionary // expected-error{{cannot convert value of type '[NSObject : NotBridgedStruct]' to type 'NSDictionary' in coercion}}
 
-  nsd = [NSObject : BridgedClass?]() // expected-error{{cannot assign a value of type '[NSObject : BridgedClass?]' to a value of type 'NSDictionary'}}
+  nsd = [NSObject : BridgedClass?]() // expected-error{{cannot assign value of type '[NSObject : BridgedClass?]' to type 'NSDictionary'}}
   nsd = [NSObject : BridgedClass?]() as NSDictionary // expected-error{{cannot convert value of type '[NSObject : BridgedClass?]' to type 'NSDictionary' in coercion}}
-  nsd = [NSObject : BridgedStruct?]()  // expected-error{{cannot assign a value of type '[NSObject : BridgedStruct?]' to a value of type 'NSDictionary'}}
+  nsd = [NSObject : BridgedStruct?]()  // expected-error{{cannot assign value of type '[NSObject : BridgedStruct?]' to type 'NSDictionary'}}
   nsd = [NSObject : BridgedStruct?]() as NSDictionary //expected-error{{cannot convert value of type '[NSObject : BridgedStruct?]' to type 'NSDictionary' in coercion}}
 
   nsd = [BridgedClass : AnyObject]()
@@ -138,12 +138,12 @@ func dictionaryToNSDictionary() {
   nsd = [OtherClass : AnyObject]() as NSDictionary
   nsd = [BridgedStruct : AnyObject]()
   nsd = [BridgedStruct : AnyObject]() as NSDictionary
-  nsd = [NotBridgedStruct : AnyObject]()  // expected-error{{cannot assign a value of type '[NotBridgedStruct : AnyObject]' to a value of type 'NSDictionary'}}
+  nsd = [NotBridgedStruct : AnyObject]()  // expected-error{{cannot assign value of type '[NotBridgedStruct : AnyObject]' to type 'NSDictionary'}}
   nsd = [NotBridgedStruct : AnyObject]() as NSDictionary  // expected-error{{cannot convert value of type '[NotBridgedStruct : AnyObject]' to type 'NSDictionary' in coercion}}
 
   // <rdar://problem/17134986>
   var bcOpt: BridgedClass?
-  nsd = [BridgedStruct() : bcOpt] // expected-error{{cannot assign a value of type '[BridgedStruct : BridgedClass?]' to a value of type 'NSDictionary'}}
+  nsd = [BridgedStruct() : bcOpt] // expected-error{{value of optional type 'BridgedClass?' not unwrapped; did you mean to use '!' or '?'?}}
   bcOpt = nil
   _ = nsd
 }

test/Constraints/diagnostics.swift

@@ -376,7 +376,7 @@ var afterMessageCount : Int? = nil
 func uintFunc() -> UInt {}
 func takeVoidVoidFn(a : () -> ()) {}
 takeVoidVoidFn { () -> Void in
-  afterMessageCount = uintFunc()  // expected-error {{cannot assign a value of type 'UInt' to a value of type 'Int?'}}
+  afterMessageCount = uintFunc()  // expected-error {{cannot assign value of type 'UInt' to type 'Int?'}}
 }
 
 // <rdar://problem/19997471> Swift: Incorrect compile error when calling a function inside a closure
@@ -425,7 +425,7 @@ zip(numbers, numbers).filter { $0.2 > 1 }  // expected-error {{value of tuple ty
 func foo20868864(callback: ([String]) -> ()) { }
 func rdar20868864(var s: String) {
   foo20868864 { (strings: [String]) in
-    s = strings   // expected-error {{cannot assign a value of type '[String]' to a value of type 'String'}}
+    s = strings   // expected-error {{cannot assign value of type '[String]' to type 'String'}}
   }
 }
 
@@ -459,8 +459,8 @@ let _: Color = .overload(1)  // expected-error {{ambiguous reference to member '
 let _: Color = .frob(1.0, &i) // expected-error {{cannot convert value of type 'Double' to expected argument type 'Int'}}
 let _: Color = .frob(1, i)  // expected-error {{passing value of type 'Int' to an inout parameter requires explicit '&'}}
 let _: Color = .frob(1, &d) // expected-error {{cannot convert value of type 'inout Double' to expected argument type 'inout Int'}}
-let _ : Color = .red // expected-error {{type 'Color' has no member 'red'}}
-
+var someColor : Color = .red // expected-error {{type 'Color' has no member 'red'}}
+someColor = .red  // expected-error {{type 'Color' has no member 'red'}}
 
 func testTypeSugar(a : Int) {
   typealias Stride = Int

test/Constraints/errortype_bridging.swift

@@ -34,7 +34,7 @@ var ns4 = compo as NSError
 
 // NSError conversion must be explicit.
 // TODO: fixit to insert 'as NSError'
-ns4 = compo // expected-error{{cannot assign a value of type 'protocol<HairyErrorType, Runcible>' to a value of type 'NSError'}}
+ns4 = compo // expected-error{{cannot assign value of type 'protocol<HairyErrorType, Runcible>' to type 'NSError'}}
 
 let e1 = ns1 as? FooError
 let e1fix = ns1 as FooError // expected-error{{did you mean to use 'as!'}} {{17-19=as!}}

test/Constraints/existential_metatypes.swift

@@ -10,23 +10,23 @@ var qp: Q.Protocol
 var pp: P.Protocol = qp // expected-error{{cannot convert value of type 'Q.Protocol' to specified type 'P.Protocol'}}
 
 var qt: Q.Type
-qt = qp // expected-error{{cannot assign a value of type 'Q.Protocol' to a value of type 'Q.Type'}}
-qp = qt // expected-error{{cannot assign a value of type 'Q.Type' to a value of type 'Q.Protocol'}}
+qt = qp // expected-error{{cannot assign value of type 'Q.Protocol' to type 'Q.Type'}}
+qp = qt // expected-error{{cannot assign value of type 'Q.Type' to type 'Q.Protocol'}}
 var pt: P.Type = qt // expected-error{{cannot convert value of type 'Q.Type' to specified type 'P.Type'}}
-pt = pp // expected-error{{cannot assign a value of type 'P.Protocol' to a value of type 'P.Type'}}
-pp = pt // expected-error{{cannot assign a value of type 'P.Type' to a value of type 'P.Protocol'}}
+pt = pp // expected-error{{cannot assign value of type 'P.Protocol' to type 'P.Type'}}
+pp = pt // expected-error{{cannot assign value of type 'P.Type' to type 'P.Protocol'}}
 
 var pqt: protocol<P, Q>.Type
 pt = pqt
 qt = pqt
 
 
 var pqp: protocol<P, Q>.Protocol
-pp = pqp // expected-error{{cannot assign}}
-qp = pqp // expected-error{{cannot assign}}
+pp = pqp // expected-error{{cannot assign value of type 'protocol<P, Q>.Protocol' to type 'P.Protocol'}}
+qp = pqp // expected-error{{cannot assign value of type 'protocol<P, Q>.Protocol' to type 'Q.Protocol'}}
 
 var ppp: PP.Protocol
-pp = ppp // expected-error{{cannot assign}}
+pp = ppp // expected-error{{cannot assign value of type 'PP.Protocol' to type 'P.Protocol'}}
 
 var ppt: PP.Type
 pt = ppt
@@ -35,8 +35,8 @@ var at: Any.Type
 at = pt
 
 var ap: Any.Protocol
-ap = pp // expected-error{{cannot assign}}
-ap = pt // expected-error{{cannot assign}}
+ap = pp // expected-error{{cannot assign value of type 'P.Protocol' to type 'Any.Protocol' (aka 'protocol<>.Protocol')}}
+ap = pt // expected-error{{cannot assign value of type 'P.Type' to type 'Any.Protocol' (aka 'protocol<>.Protocol')}}
 
 // Meta-metatypes