Merge pull request #63145 from LucianoPAlmeida/nil-placeholders

[Sema] Record specify contextual type for nil in placeholder context

Author: LucianoPAlmeida

lib/Sema/CSBindings.cpp

@@ -2147,6 +2147,14 @@ TypeVariableBinding::fixForHole(ConstraintSystem &cs) const {
   }
 
   if (srcLocator->isLastElement<LocatorPathElt::PlaceholderType>()) {
+    // When a 'nil' has a placeholder as contextual type there is not enough
+    // information to resolve it, so let's record a specify contextual type for
+    // nil fix.
+    if (isExpr<NilLiteralExpr>(srcLocator->getAnchor())) {
+      ConstraintFix *fix = SpecifyContextualTypeForNil::create(cs, dstLocator);
+      return std::make_pair(fix, /*impact=*/(unsigned)10);
+    }
+
     ConstraintFix *fix = SpecifyTypeForPlaceholder::create(cs, srcLocator);
     return std::make_pair(fix, defaultImpact);
   }

test/Sema/placeholder_type.swift

@@ -266,3 +266,7 @@ func deferredInit(_ c: Bool) {
     x = "Goodbye"
   }
 }
+
+// https://github.com/apple/swift/issues/63130
+let _: _  = nil // expected-error{{'nil' requires a contextual type}}
+let _: _? = nil // expected-error{{'nil' requires a contextual type}}