[Sema] [SR-4347] Improve inference of optional supertypes

lib/Sema/CSSolver.cpp

@@ -1173,22 +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();
-      if (!nominalBindingDecl) continue;
-      SmallVector<ProtocolConformance *, 2> conformances;
-      if (!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 (wrapInOptional) {
         binding.BindingType = OptionalType::get(binding.BindingType);
       }
     }

test/Constraints/array_literal.swift

@@ -121,32 +121,47 @@ 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 = []
+
+  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 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'.
-func joinWithNil(s: String) {
+protocol Proto1 {}
+protocol Proto2 {}
+struct Nilable: ExpressibleByNilLiteral {
+	init(nilLiteral: ()) {}
+}
+func joinWithNil<T>(s: String, a: Any, t: T, m: T.Type, p: Proto1 & Proto2, arr: [Int], opt: Int?, iou: Int!, n: Nilable) {
   let a1 = [s, nil]
   let _: Int = a1 // expected-error{{value of type '[String?]'}}
 
@@ -158,6 +173,72 @@ func joinWithNil(s: String) {
 
   let a4 = [nil, "hello"]
   let _: Int = a4 // expected-error{{value of type '[String?]'}}
+
+  let a5 = [(s, s), nil]
+  let _: Int = a5 // expected-error{{value of type '[(String, String)?]'}}
+
+  let a6 = [nil, (s, s)]
+  let _: Int = a6 // expected-error{{value of type '[(String, String)?]'}}
+
+  let a7 = [("hello", "world"), nil]
+  let _: Int = a7 // expected-error{{value of type '[(String, String)?]'}}
+
+  let a8 = [nil, ("hello", "world")]
+  let _: Int = a8 // expected-error{{value of type '[(String, String)?]'}}
+
+  let a9 = [{ $0 * 2 }, nil]
+  let _: Int = a9 // expected-error{{value of type '[((Int) -> Int)?]'}}
+
+  let a10 = [nil, { $0 * 2 }]
+  let _: Int = a10 // expected-error{{value of type '[((Int) -> Int)?]'}}
+
+  let a11 = [a, nil]
+  let _: Int = a11 // expected-error{{value of type '[Any?]'}}
+
+  let a12 = [nil, a]
+  let _: Int = a12 // expected-error{{value of type '[Any?]'}}
+
+  let a13 = [t, nil]
+  let _: Int = a13 // expected-error{{value of type '[T?]'}}
+
+  let a14 = [nil, t]
+  let _: Int = a14 // expected-error{{value of type '[T?]'}}
+
+  let a15 = [m, nil]
+  let _: Int = a15 // expected-error{{value of type '[T.Type?]'}}
+
+  let a16 = [nil, m]
+  let _: Int = a16 // expected-error{{value of type '[T.Type?]'}}
+
+  let a17 = [p, nil]
+  let _: Int = a17 // expected-error{{value of type '[(Proto1 & Proto2)?]'}}
+
+  let a18 = [nil, p]
+  let _: Int = a18 // expected-error{{value of type '[(Proto1 & Proto2)?]'}}
+
+  let a19 = [arr, nil]
+  let _: Int = a19 // expected-error{{value of type '[[Int]?]'}}
+
+  let a20 = [nil, arr]
+  let _: Int = a20 // expected-error{{value of type '[[Int]?]'}}
+
+  let a21 = [opt, nil]
+  let _: Int = a21 // expected-error{{value of type '[Int?]'}}
+
+  let a22 = [nil, opt]
+  let _: Int = a22 // expected-error{{value of type '[Int?]'}}
+
+  let a23 = [iou, nil]
+  let _: Int = a23 // expected-error{{value of type '[Int?]'}}
+
+  let a24 = [nil, iou]
+  let _: Int = a24 // expected-error{{value of type '[Int?]'}}
+
+  let a25 = [n, nil]
+  let _: Int = a25 // expected-error{{value of type '[Nilable]'}}
+
+  let a26 = [nil, n]
+  let _: Int = a26 // expected-error{{value of type '[Nilable]'}}
 }
 
 struct OptionSetLike : ExpressibleByArrayLiteral {

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}}

test/Constraints/optional.swift

@@ -120,7 +120,12 @@ func testVoidOptional() {
   voidOptional(optNoop)
 }
 
-func testTernaryWithNil(b: Bool, s: String, i: Int) {
+protocol Proto1 {}
+protocol Proto2 {}
+struct Nilable: ExpressibleByNilLiteral {
+	init(nilLiteral: ()) {}
+}
+func testTernaryWithNil<T>(b: Bool, s: String, i: Int, a: Any, t: T, m: T.Type, p: Proto1 & Proto2, arr: [Int], opt: Int?, iou: Int!, n: Nilable) {
   let t1 = b ? s : nil
   let _: Double = t1 // expected-error{{value of type 'String?'}}
   let t2 = b ? nil : i
@@ -129,6 +134,50 @@ func testTernaryWithNil(b: Bool, s: String, i: Int) {
   let _: Double = t3 // expected-error{{value of type 'String?'}}
   let t4 = b ? nil : 1
   let _: Double = t4 // expected-error{{value of type 'Int?'}}
+  let t5 = b ? (s, i) : nil
+  let _: Double = t5 // expected-error{{value of type '(String, Int)?}}
+  let t6 = b ? nil : (i, s)
+  let _: Double = t6 // expected-error{{value of type '(Int, String)?}}
+  let t7 = b ? ("hello", 1) : nil
+  let _: Double = t7 // expected-error{{value of type '(String, Int)?}}
+  let t8 = b ? nil : (1, "hello")
+  let _: Double = t8 // expected-error{{value of type '(Int, String)?}}
+  let t9 = b ? { $0 * 2 } : nil
+  let _: Double = t9 // expected-error{{value of type '((Int) -> Int)?}}
+  let t10 = b ? nil : { $0 * 2 }
+  let _: Double = t10 // expected-error{{value of type '((Int) -> Int)?}}
+  let t11 = b ? a : nil
+  let _: Double = t11 // expected-error{{value of type 'Any?'}}
+  let t12 = b ? nil : a
+  let _: Double = t12 // expected-error{{value of type 'Any?'}}
+  let t13 = b ? t : nil
+  let _: Double = t13 // expected-error{{value of type 'T?'}}
+  let t14 = b ? nil : t
+  let _: Double = t14 // expected-error{{value of type 'T?'}}
+  let t15 = b ? m : nil
+  let _: Double = t15 // expected-error{{value of type 'T.Type?'}}
+  let t16 = b ? nil : m
+  let _: Double = t16 // expected-error{{value of type 'T.Type?'}}
+  let t17 = b ? p : nil
+  let _: Double = t17 // expected-error{{value of type '(Proto1 & Proto2)?'}}
+  let t18 = b ? nil : p
+  let _: Double = t18 // expected-error{{value of type '(Proto1 & Proto2)?'}}
+  let t19 = b ? arr : nil
+  let _: Double = t19 // expected-error{{value of type '[Int]?'}}
+  let t20 = b ? nil : arr
+  let _: Double = t20 // expected-error{{value of type '[Int]?'}}
+  let t21 = b ? opt : nil
+  let _: Double = t21 // expected-error{{value of type 'Int?'}}
+  let t22 = b ? nil : opt
+  let _: Double = t22 // expected-error{{value of type 'Int?'}}
+  let t23 = b ? iou : nil
+  let _: Double = t23 // expected-error{{value of type 'Int?'}}
+  let t24 = b ? nil : iou
+  let _: Double = t24 // expected-error{{value of type 'Int?'}}
+  let t25 = b ? n : nil
+  let _: Double = t25 // expected-error{{value of type 'Nilable'}}
+  let t26 = b ? nil : n
+  let _: Double = t26 // expected-error{{value of type 'Nilable'}}
 }
 
 // inference with IUOs