[Diagnostics] Improve error when type parameters aren't equal

include/swift/AST/DiagnosticsSema.def

@@ -1429,9 +1429,6 @@ NOTE(type_does_not_inherit_or_conform_requirement,none,
 ERROR(types_not_equal,none,
       "%0 requires the types %1 and %2 be equivalent",
       (Type, Type, Type))
-ERROR(types_not_equal_in_call,none,
-      "%0 requires the types %1 and %2 be equivalent to use %3",
-      (Type, Type, Type, DeclName))
 ERROR(type_does_not_conform_owner,none,
       "%0 requires that %1 conform to %2", (Type, Type, Type))
 NOTE(requirement_implied_by_conditional_conformance,none,

lib/Sema/CSDiag.cpp

@@ -1704,6 +1704,77 @@ bool FailureDiagnosis::diagnoseConversionToBool(Expr *expr, Type exprType) {
   return false;
 }
 
+static bool
+diagnoseUnresolvedDotExprTypeRequirementFailure(ConstraintSystem &cs,
+                                                Constraint *constraint) {
+  auto &TC = cs.TC;
+
+  auto *locator = constraint->getLocator();
+  if (!locator)
+    return false;
+
+  auto path = locator->getPath();
+  if (path.empty())
+    return false;
+
+  auto &last = path.back();
+  if (last.getKind() != ConstraintLocator::TypeParameterRequirement)
+    return false;
+
+  auto *anchor = locator->getAnchor();
+  if (!anchor)
+    return false;
+
+  auto *UDE = dyn_cast<UnresolvedDotExpr>(anchor);
+  if (!UDE)
+    return false;
+
+  auto ownerType = cs.getType(UDE->getBase());
+  if (!ownerType)
+    return false;
+
+  ownerType = cs.simplifyType(ownerType)->getWithoutSpecifierType();
+  if (ownerType->hasTypeVariable() || ownerType->hasUnresolvedType())
+    return false;
+
+  // If we actually resolved the member to use, use it.
+  auto loc = cs.getConstraintLocator(UDE, ConstraintLocator::Member);
+  auto *member = cs.findResolvedMemberRef(loc);
+  if (!member)
+    return false;
+
+  auto req = member->getAsGenericContext()
+                 ->getGenericSignature()
+                 ->getRequirements()[last.getValue()];
+
+  Diag<Type, Type, Type, Type, StringRef> note;
+  switch (req.getKind()) {
+  case RequirementKind::Conformance:
+  case RequirementKind::Layout:
+    return false;
+
+  case RequirementKind::Superclass:
+    note = diag::candidate_types_inheritance_requirement;
+    break;
+
+  case RequirementKind::SameType:
+    note = diag::candidate_types_equal_requirement;
+    break;
+  }
+
+  TC.diagnose(UDE->getLoc(), diag::could_not_find_value_member, ownerType,
+              UDE->getName());
+
+  auto first = cs.simplifyType(constraint->getFirstType());
+  auto second = cs.simplifyType(constraint->getSecondType());
+  auto rawFirstType = req.getFirstType();
+  auto rawSecondType = req.getSecondType();
+
+  TC.diagnose(member, note, first, second, rawFirstType, rawSecondType, "");
+
+  return true;
+}
+
 /// Diagnose problems related to failures in constraints
 /// generated by `openGeneric` which represent different
 /// kinds of type parameter requirements.
@@ -1741,6 +1812,9 @@ static bool diagnoseTypeRequirementFailure(ConstraintSystem &cs,
   if (ownerType->hasTypeVariable() || ownerType->hasUnresolvedType())
     return false;
 
+  if (diagnoseUnresolvedDotExprTypeRequirementFailure(cs, constraint))
+    return true;
+
   auto lhs = cs.simplifyType(constraint->getFirstType());
   auto rhs = cs.simplifyType(constraint->getSecondType());
 
@@ -1756,12 +1830,7 @@ static bool diagnoseTypeRequirementFailure(ConstraintSystem &cs,
     return true;
 
   case ConstraintKind::Equal: { // same type
-    if (auto *UDE = dyn_cast<UnresolvedDotExpr>(anchor)) {
-      TC.diagnose(UDE->getLoc(), diag::types_not_equal_in_call, ownerType, lhs,
-                  rhs, UDE->getName());
-    } else {
-      TC.diagnose(anchor->getLoc(), diag::types_not_equal, ownerType, lhs, rhs);
-    }
+    TC.diagnose(anchor->getLoc(), diag::types_not_equal, ownerType, lhs, rhs);
     return true;
   }
 

test/Constraints/generics.swift

@@ -559,7 +559,7 @@ do {
 }
 
 func rdar35890334(_ arr: inout [Int]) {
-  _ = arr.popFirst() // expected-error {{'[Int]' requires the types '[Int]' and 'ArraySlice<Int>' be equivalent to use 'popFirst'}}
+  _ = arr.popFirst() // expected-error {{value of type '[Int]' has no member 'popFirst'}}
 }
 
 // rdar://problem/39616039

test/decl/ext/protocol.swift

@@ -207,7 +207,7 @@ struct S4d : P4 {
 }
 
 extension P4 where Self.AssocP4 == Int {
-  func extP4Int() { }
+  func extP4Int() { } // expected-note {{candidate requires that the types 'Bool' and 'Int' be equivalent (requirement specified as 'Self.AssocP4' == 'Int')}}
 }
 
 extension P4 where Self.AssocP4 == Bool {
@@ -221,7 +221,7 @@ func testP4(_ s4a: S4a, s4b: S4b, s4c: S4c, s4d: S4d) {
   s4c.extP4Int() // okay
   var b1 = s4d.extP4a() // okay, "Bool" version
   b1 = true // checks type above
-  s4d.extP4Int() // expected-error{{'S4d' requires the types 'Bool' and 'Int' be equivalent to use 'extP4Int'}}
+  s4d.extP4Int() // expected-error{{value of type 'S4d' has no member 'extP4Int'}}
   _ = b1
 }
 

test/decl/protocol/protocols.swift

@@ -266,7 +266,7 @@ struct WrongIsEqual : IsEqualComparable { // expected-error{{type 'WrongIsEqual'
 //===----------------------------------------------------------------------===//
 
 func existentialSequence(_ e: Sequence) { // expected-error{{has Self or associated type requirements}}
-  var x = e.makeIterator() // expected-error{{'Sequence' requires the types 'Sequence' and 'Sequence.Iterator' be equivalent to use 'makeIterator'}}
+  var x = e.makeIterator() // expected-error{{value of type 'Sequence' has no member 'makeIterator'}}
   x.next()
   x.nonexistent()
 }