[Diagnostics] Check whether missing conformance could be fixed by using .rawValue

A lot of operators (and most likely regular functions a well) have
overloads that accept i.e. a generic parameter that conforms to
`StringProtocol`, so the best fix in situations when argument is
a raw representable type would be to check whether `.rawValue`
conforms to the expected protocol and use it if so.

Resolves rdar://problem/75367157

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -6841,6 +6841,8 @@ AbstractRawRepresentableFailure::getDiagnostic() const {
     return diag::cannot_convert_assign;
   } else if (locator->isLastElement<LocatorPathElt::ApplyArgToParam>()) {
     return diag::cannot_convert_argument_value;
+  } else if (locator->isLastElement<LocatorPathElt::AnyRequirement>()) {
+    return diag::cannot_convert_initializer_value_protocol;
   }
 
   return None;

lib/Sema/CSSimplify.cpp

@@ -6013,6 +6013,14 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
         }
       }
 
+      if (auto rawValue = isRawRepresentable(*this, type)) {
+        if (!rawValue->isTypeVariableOrMember() &&
+            TypeChecker::conformsToProtocol(rawValue, protocol, DC)) {
+          auto *fix = UseRawValue::create(*this, type, protocolTy, loc);
+          return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
+        }
+      }
+
       auto anchor = locator.getAnchor();
 
       if (isExpr<UnresolvedMemberExpr>(anchor) &&
@@ -10751,7 +10759,6 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AddPropertyWrapperAttribute:
   case FixKind::ExpandArrayIntoVarargs:
   case FixKind::UseRawValue:
-  case FixKind::ExplicitlyConstructRawRepresentable:
   case FixKind::SpecifyBaseTypeForContextualMember:
   case FixKind::CoerceToCheckedCast:
   case FixKind::SpecifyObjectLiteralTypeImport:
@@ -10772,6 +10779,17 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
     return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
   }
 
+  case FixKind::ExplicitlyConstructRawRepresentable: {
+    // Let's increase impact of this fix for binary operators because
+    // it's possible to get both `.rawValue` and construction fixes for
+    // different overloads of a binary operator and `.rawValue` is a
+    // better fix because raw representable has a failable constructor.
+    return recordFix(fix,
+                     /*impact=*/isExpr<BinaryExpr>(locator.getAnchor()) ? 2 : 1)
+               ? SolutionKind::Error
+               : SolutionKind::Solved;
+  }
+
   case FixKind::TreatRValueAsLValue: {
     unsigned impact = 1;
     // If this is an attempt to use result of a function/subscript call as

test/ClangImporter/newtype_conformance.swift

@@ -16,12 +16,11 @@ func acceptHashable<T: Hashable>(_: T) {}
 // expected-note@-1 {{where 'T' = 'WrappedRef'}}
 // expected-note@-2 {{where 'T' = 'WrappedValue'}}
 func acceptComparable<T: Comparable>(_: T) {}
-// expected-note@-1 {{where 'T' = 'NSNotification.Name'}}
 
 func testNewTypeWrapper(x: NSNotification.Name, y: NSNotification.Name) {
   acceptEquatable(x)
   acceptHashable(x)
-  acceptComparable(x) // expected-error {{global function 'acceptComparable' requires that 'NSNotification.Name' conform to 'Comparable'}}
+  acceptComparable(x) // expected-error {{value of type 'NSNotification.Name' does not conform to specified type 'Comparable'}} {{19-19=.rawValue}}
 
   _ = x == y
   _ = x != y

test/Constraints/fixes.swift

@@ -359,5 +359,5 @@ func testKeyPathSubscriptArgFixes(_ fn: @escaping () -> Int) {
 
 func sr12426(a: Any, _ str: String?) {
   a == str // expected-error {{binary operator '==' cannot be applied to operands of type 'Any' and 'String?'}}
-  // expected-note@-1 {{overloads for '==' exist with these partially matching parameter lists: (CodingUserInfoKey, CodingUserInfoKey), (String, String)}}
+  // expected-note@-1 {{overloads for '==' exist with these partially matching parameter lists: (String, String)}}
 }

validation-test/Sema/SwiftUI/rdar75367157.swift

@@ -0,0 +1,30 @@
+// RUN: %target-typecheck-verify-swift -target x86_64-apple-macosx10.15 -swift-version 5
+// REQUIRES: objc_interop
+// REQUIRES: OS=macosx
+
+import SwiftUI
+
+enum E : String {
+  case a
+  case b
+
+  var description: String { get { "" } }
+}
+
+struct S : View {
+  var test: E = .a
+
+  func check(_: String) -> Bool {}
+
+  var body: some View {
+    List {
+      if test != E.b.description { // expected-error {{cannot convert value of type 'E' to expected argument type 'String'}} {{14-14=.rawValue}}
+        EmptyView()
+      }
+
+      if (check(self.test)) { // expected-error {{cannot convert value of type 'E' to expected argument type 'String'}} {{26-26=.rawValue}}
+        Spacer()
+      }
+    }
+  }
+}