[Diagnostics] Add support for new "ternary branch" element to contextual mismatch

Author: xedin

lib/Sema/CSDiag.cpp

@@ -248,7 +248,6 @@ class FailureDiagnosis :public ASTVisitor<FailureDiagnosis, /*exprresult*/bool>{
   bool visitSubscriptExpr(SubscriptExpr *SE);
   bool visitApplyExpr(ApplyExpr *AE);
   bool visitCoerceExpr(CoerceExpr *CE);
-  bool visitIfExpr(IfExpr *IE);
   bool visitRebindSelfInConstructorExpr(RebindSelfInConstructorExpr *E);
 };
 } // end anonymous namespace
@@ -1890,37 +1889,6 @@ bool FailureDiagnosis::visitCoerceExpr(CoerceExpr *CE) {
   return false;
 }
 
-bool FailureDiagnosis::visitIfExpr(IfExpr *IE) {
-  auto typeCheckClauseExpr = [&](Expr *clause, Type contextType = Type(),
-                                 ContextualTypePurpose convertPurpose =
-                                     CTP_Unused) -> Expr * {
-    // Provide proper contextual type when type conversion is specified.
-    return typeCheckChildIndependently(clause, contextType, convertPurpose,
-                                       TCCOptions(), nullptr, false);
-  };
-  // Check all of the subexpressions independently.
-  auto condExpr = typeCheckClauseExpr(IE->getCondExpr());
-  if (!condExpr) return true;
-  auto trueExpr = typeCheckClauseExpr(IE->getThenExpr(), CS.getContextualType(),
-                                      CS.getContextualTypePurpose());
-  if (!trueExpr) return true;
-  auto falseExpr = typeCheckClauseExpr(
-      IE->getElseExpr(), CS.getContextualType(), CS.getContextualTypePurpose());
-  if (!falseExpr) return true;
-
-  // If the true/false values already match, it must be a contextual problem.
-  if (CS.getType(trueExpr)->isEqual(CS.getType(falseExpr)))
-    return false;
-  
-  // Otherwise, the true/false result types must not be matching.
-  diagnose(IE->getColonLoc(), diag::if_expr_cases_mismatch,
-           CS.getType(trueExpr), CS.getType(falseExpr))
-      .highlight(trueExpr->getSourceRange())
-      .highlight(falseExpr->getSourceRange());
-  return true;
-}
-
-
 bool FailureDiagnosis::
 visitRebindSelfInConstructorExpr(RebindSelfInConstructorExpr *E) {
   // Don't walk the children for this node, it leads to multiple diagnostics

lib/Sema/CSDiagnostics.cpp

@@ -1906,6 +1906,14 @@ bool ContextualFailure::diagnoseAsError() {
     break;
   }
 
+  case ConstraintLocator::TernaryBranch: {
+    auto *ifExpr = cast<IfExpr>(getRawAnchor());
+    fromType = getType(ifExpr->getThenExpr());
+    toType = getType(ifExpr->getElseExpr());
+    diagnostic = diag::if_expr_cases_mismatch;
+    break;
+  }
+
   case ConstraintLocator::ContextualType: {
     if (diagnoseConversionToBool())
       return true;