[FixCode] Add diagnosis/fixit to help users deal with BooleanType's removal (#4392)

* [FixCode] Add diagnosis/fixit to help users deal with BooleanType's removal.

Due to migration reasons, types used to conform to BooleanType, which
must contain a member var 'boolValue', now does not convert to Bool. This patch
adds a specific diagnosis/fixit to explicitly invoke 'boolValue' to please the
context types.

* Address Jordan's code review comments.

Author: nkcsgexi

include/swift/AST/DiagnosticsSema.def

@@ -681,6 +681,9 @@ NOTE(in_cast_expr_types,none,
       "in cast from type %0 to %1",
       (Type, Type))
 
+ERROR(types_not_convertible_use_bool_value,none,
+      "%0 is not convertible to %1; did you mean %0.boolValue", (Type, Type))
+
 ERROR(tuple_types_not_convertible_nelts,none,
       "%0 is not convertible to %1, "
       "tuples have a different number of elements", (Type, Type))

lib/Sema/CSDiag.cpp

@@ -2914,6 +2914,27 @@ bool FailureDiagnosis::diagnoseGeneralConversionFailure(Constraint *constraint){
     }
     return true;
   }
+
+  // Due to migration reasons, types used to conform to BooleanType, which
+  // contain a member var 'boolValue', now does not convert to Bool. This block
+  // tries to add a specific diagnosis/fixit to explicitly invoke 'boolValue'.
+  if (toType->isBool()) {
+    auto LookupResult = CS->TC.lookupMember(CS->DC, fromType,
+      DeclName(CS->TC.Context.getIdentifier("boolValue")));
+    if (!LookupResult.empty()) {
+      if (isa<VarDecl>(LookupResult.begin()->Decl)) {
+        if (anchor->canAppendCallParentheses())
+          diagnose(anchor->getLoc(), diag::types_not_convertible_use_bool_value,
+                   fromType, toType).fixItInsertAfter(anchor->getEndLoc(),
+                                                      ".boolValue");
+        else
+          diagnose(anchor->getLoc(), diag::types_not_convertible_use_bool_value,
+            fromType, toType).fixItInsert(anchor->getStartLoc(), "(").
+              fixItInsertAfter(anchor->getEndLoc(), ").boolValue");
+        return true;
+      }
+    }
+  }
 
   diagnose(anchor->getLoc(), diag::types_not_convertible,
            constraint->getKind() == ConstraintKind::Subtype,

test/FixCode/fixits-apply.swift

@@ -118,7 +118,7 @@ func baz(var x: Int) {
   x += 10
 }
 func foo(let y: String, inout x: Int) {
-  
+
 }
 
 struct Test1 : OptionSet {
@@ -261,3 +261,12 @@ func disable_unnamed_param_reorder(p: Int, _: String) {}
 disable_unnamed_param_reorder(0, "") // no change.
 
 prefix operator ***** {}
+
+class BoolFoo : BooleanType {
+  var boolValue: Bool {return false}
+}
+func testBoolValue(a : BoolFoo) {
+  if a { }
+  guard a {}
+  if a as BoolFoo {}
+}

test/FixCode/fixits-apply.swift.result

@@ -121,7 +121,7 @@ func baz(x: Int) {
   x += 10
 }
 func foo(y: String, x: inout Int) {
-  
+
 }
 
 struct Test1 : OptionSet {
@@ -264,3 +264,12 @@ func disable_unnamed_param_reorder(p: Int, _: String) {}
 disable_unnamed_param_reorder(0, "") // no change.
 
 prefix operator *****
+
+class BoolFoo : Bool {
+  var boolValue: Bool {return false}
+}
+func testBoolValue(a : BoolFoo) {
+  if a.boolValue { }
+  guard a.boolValue {}
+  if (a as BoolFoo).boolValue {}
+}