Merge pull request #76487 from xedin/fix-invalid-binding-elision

[CSBindings] Prevent `BindingSet::isViable` from dropping viable bindings

Author: xedin

lib/Sema/CSBindings.cpp

@@ -1205,6 +1205,16 @@ bool BindingSet::isViable(PotentialBinding &binding, bool isTransitive) {
     if (!existingNTD || NTD != existingNTD)
       continue;
 
+    // What is going on here needs to be thoroughly re-evaluated,
+    // but at least for now, let's not filter bindings of different
+    // kinds so if we have a situation like: `Array<$T0> conv $T1`
+    // and `$T1 conv Array<(String, Int)>` we can't lose `Array<$T0>`
+    // as a binding because `$T0` could be inferred to
+    // `(key: String, value: Int)` and binding `$T1` to `Array<(String, Int)>`
+    // eagerly would be incorrect.
+    if (existing->Kind != binding.Kind)
+      continue;
+
     // If new type has a type variable it shouldn't
     // be considered  viable.
     if (type->hasTypeVariable())

test/Constraints/array_literal.swift

@@ -415,3 +415,13 @@ do {
     ]
   }
 }
+
+
+do {
+  func f<R>(fn: () -> [R]) -> [R] { [] }
+
+  // Requires collection upcast from Array<(key: String, value: String)> to `Array<(String, String)>`
+  func g(v: [String: String]) {
+    let _: [(String, String)] = f { return Array(v) } + v // Ok
+  }
+}

validation-test/Sema/SwiftUI/rdar98862079.swift

@@ -22,7 +22,7 @@ struct MyView : View {
 
   var body: some View {
     test(value: true ? $newBounds.maxBinding : $newBounds.minBinding, in: bounds)
-    // expected-error@-1 2 {{result values in '? :' expression have mismatching types 'Binding<Binding<Double>?>' and 'Binding<Double>'}}
-    // expected-note@-2 2 {{arguments to generic parameter 'Value' ('Binding<Double>?' and 'Double') are expected to be equal}}
+    // expected-error@-1 {{cannot convert value of type 'Binding<Binding<Double>?>' to expected argument type 'Binding<Double>'}}
+    // expected-note@-2 {{arguments to generic parameter 'Value' ('Binding<Double>?' and 'Double') are expected to be equal}}
   }
 }