[ConstraintSystem] Increase impact of fixes for some conditional requirements

If there is a conditional requirement failure associated with
member/function reference used in a call let's increase a score
of a fix for such failure because it renders member/function
unreachable in current context or with a given set of arguments.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -1449,6 +1449,20 @@ assessRequirementFailureImpact(ConstraintSystem &cs, Type requirementType,
   if (!anchor)
     return impact;
 
+  // If this is a conditional requirement failure associated with a
+  // call, let's increase impact of the fix to show that such failure
+  // makes member/function unreachable in current context or with
+  // given arguments.
+  if (auto last = locator.last()) {
+    if (last->isConditionalRequirement()) {
+      if (auto *expr = getAsExpr(anchor)) {
+        auto *parent = cs.getParentExpr(expr);
+        if (parent && isa<ApplyExpr>(parent))
+          return 5;
+      }
+    }
+  }
+
   // If this requirement is associated with a member reference and it
   // was possible to check it before overload choice is bound, that means
   // types came from the context (most likely Self, or associated type(s))

test/Constraints/bridging.swift

@@ -180,7 +180,7 @@ func dictionaryToNSDictionary() {
 // In this case, we should not implicitly convert Dictionary to NSDictionary.
 struct NotEquatable {}
 func notEquatableError(_ d: Dictionary<Int, NotEquatable>) -> Bool {
-  return d == d // expected-error{{operator function '==' requires that 'NotEquatable' conform to 'Equatable'}}
+  return d == d // expected-error{{referencing operator function '==' on 'Dictionary' requires that 'NotEquatable' conform to 'Equatable'}}
 }
 
 // NSString -> String

test/Constraints/operator.swift

@@ -220,7 +220,7 @@ func rdar46459603() {
   // expected-error@-1 {{referencing operator function '==' on 'Equatable' requires that 'Dictionary<String, E>.Values' conform to 'Equatable'}}
   // expected-error@-2 {{cannot convert value of type '[E]' to expected argument type 'Dictionary<String, E>.Values'}}
   _ = [arr.values] == [[e]]
-  // expected-error@-1 {{operator function '==' requires that 'Dictionary<String, E>.Values' conform to 'Equatable'}}
+  // expected-error@-1 {{referencing operator function '==' on 'Array' requires that 'Dictionary<String, E>.Values' conform to 'Equatable'}}
   // expected-error@-2 {{cannot convert value of type '[E]' to expected element type 'Dictionary<String, E>.Values'}}
 }
 

test/Generics/conditional_conformances.swift

@@ -413,9 +413,9 @@ extension Foo: P where Bar: P {
 extension BinaryInteger {
   var foo: Self {
     return self <= 1
-            ? 1
+            ? 1 // expected-error {{cannot convert return expression of type 'Int' to return type 'Self'}}
             : (2...self).reduce(1, *)
-            // expected-error@-1 {{referencing instance method 'reduce' on 'ClosedRange' requires that 'Self.Stride' conform to 'SignedInteger'}}
+            // expected-error@-1 {{cannot convert value of type 'Self' to expected argument type 'Int'}} {{20-20=Int(}} {{24-24=)}}
   }
 }
 

test/Parse/pointer_conversion.swift.gyb

@@ -307,7 +307,7 @@ struct NotEquatable {}
 func arrayComparison(_ x: [NotEquatable], y: [NotEquatable], p: UnsafeMutablePointer<NotEquatable>) {
   var x = x
   // Don't allow implicit array-to-pointer conversions in operators.
-  let a: Bool = x == y // expected-error{{operator function '==' requires that 'NotEquatable' conform to 'Equatable'}}
+  let a: Bool = x == y // expected-error{{referencing operator function '==' on 'Array' requires that 'NotEquatable' conform to 'Equatable'}}
   let _: Bool = p == &x  // Allowed!
 }
 

test/stdlib/ArrayDiagnostics.swift

@@ -4,5 +4,5 @@ class NotEquatable {}
 
 func test_ArrayOfNotEquatableIsNotEquatable() {
   var a = [ NotEquatable(), NotEquatable() ]
-  if a == a {} // expected-error {{operator function '==' requires that 'NotEquatable' conform to 'Equatable'}}
+  if a == a {} // expected-error {{referencing operator function '==' on 'Array' requires that 'NotEquatable' conform to 'Equatable'}}
 }