[SR-4347] default to Any? instead of Any if there is a nil literal

Author: tonisuter

lib/Sema/CSSolver.cpp

@@ -1173,26 +1173,30 @@ static PotentialBindings getPotentialBindings(ConstraintSystem &cs,
   // If we're supposed to add optional supertype bindings, do so now.
   if (addOptionalSupertypeBindings) {
     for (unsigned i : indices(result.Bindings)) {
-      // Only interested in supertype bindings.
       auto &binding = result.Bindings[i];
-      if (binding.Kind != AllowedBindingKind::Supertypes) continue;
-
-      // If the type doesn't conform to ExpressibleByNilLiteral,
-      // produce an optional of that type as a potential binding. We
-      // overwrite the binding in place because the non-optional type
-      // will fail to type-check against the nil-literal conformance.
-      auto nominalBindingDecl = binding.BindingType->getAnyNominal();
-      bool conformsToExprByNilLiteral = false;
-      if (nominalBindingDecl) {
-        SmallVector<ProtocolConformance *, 2> conformances;
-        conformsToExprByNilLiteral = nominalBindingDecl->lookupConformance(
-                                       cs.DC->getParentModule(),
-                                       cs.getASTContext().getProtocol(
-                                         KnownProtocolKind::ExpressibleByNilLiteral),
-                                       conformances);
+      bool wrapInOptional = false;
+        
+      if (binding.Kind == AllowedBindingKind::Supertypes) {
+        // If the type doesn't conform to ExpressibleByNilLiteral,
+        // produce an optional of that type as a potential binding. We
+        // overwrite the binding in place because the non-optional type
+        // will fail to type-check against the nil-literal conformance.
+        auto nominalBindingDecl = binding.BindingType->getAnyNominal();
+        bool conformsToExprByNilLiteral = false;
+        if (nominalBindingDecl) {
+          SmallVector<ProtocolConformance *, 2> conformances;
+          conformsToExprByNilLiteral = nominalBindingDecl->lookupConformance(
+                                         cs.DC->getParentModule(),
+                                         cs.getASTContext().getProtocol(
+                                           KnownProtocolKind::ExpressibleByNilLiteral),
+                                         conformances);
+        }
+        wrapInOptional = !conformsToExprByNilLiteral;
+      } else if (binding.isDefaultableBinding() && binding.BindingType->isAny()) {
+        wrapInOptional = true;
       }
 
-      if (!conformsToExprByNilLiteral) {
+      if (wrapInOptional) {
         binding.BindingType = OptionalType::get(binding.BindingType);
       }
     }

test/Constraints/array_literal.swift

@@ -121,28 +121,38 @@ class A { }
 class B : A { }
 class C : A { }
 
-/// Check for defaulting the element type to 'Any'.
+/// Check for defaulting the element type to 'Any' / 'Any?'.
 func defaultToAny(i: Int, s: String) {
   let a1 = [1, "a", 3.5]
   // expected-error@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
   let _: Int = a1  // expected-error{{value of type '[Any]'}}
 
   let a2: Array = [1, "a", 3.5]
   // expected-error@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
-
   let _: Int = a2  // expected-error{{value of type '[Any]'}}
+  
+  let a3 = [1, "a", nil, 3.5]
+  // expected-error@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
+  let _: Int = a3 // expected-error{{value of type '[Any?]'}}
+  
+  let a4: Array = [1, "a", nil, 3.5]
+  // expected-error@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
+  let _: Int = a4 // expected-error{{value of type '[Any?]'}}
 
-  let a3 = []
+  let a5 = []
   // expected-error@-1{{empty collection literal requires an explicit type}}
-
-  let _: Int = a3 // expected-error{{value of type '[Any]'}}
+  let _: Int = a5 // expected-error{{value of type '[Any]'}}
 
   let _: [Any] = [1, "a", 3.5]
   let _: [Any] = [1, "a", [3.5, 3.7, 3.9]]
   let _: [Any] = [1, "a", [3.5, "b", 3]]
+  
+  let _: [Any?] = [1, "a", nil, 3.5]
+  let _: [Any?] = [1, "a", nil, [3.5, 3.7, 3.9]]
+  let _: [Any?] = [1, "a", nil, [3.5, "b", nil]]
 
-  let a4 = [B(), C()]
-  let _: Int = a4 // expected-error{{value of type '[A]'}}
+  let a6 = [B(), C()]
+  let _: Int = a6 // expected-error{{value of type '[A]'}}
 }
 
 /// Check handling of 'nil'.

test/Constraints/dictionary_literal.swift

@@ -72,6 +72,11 @@ func testDefaultExistentials() {
   // expected-error@-1{{heterogeneous collection literal could only be inferred to 'Dictionary<String, Any>'; add explicit type annotation if this is intentional}}{{46-46= as Dictionary<String, Any>}}
 
   let _: [String : Any] = ["a" : 1, "b" : 2.5, "c" : "hello"]
+  
+  let _ = ["a" : 1, "b" : nil, "c" : "hello"]
+  // expected-error@-1{{heterogeneous collection literal could only be inferred to 'Dictionary<String, Any?>' (aka 'Dictionary<String, Optional<Any>>'); add explicit type annotation if this is intentional}}{{46-46= as Dictionary<String, Any?>}}
+  
+  let _: [String : Any?] = ["a" : 1, "b" : nil, "c" : "hello"]
 
   let d2 = [:]
   // expected-error@-1{{empty collection literal requires an explicit type}}