unified: Test that writebacks after a mutating call works

Author: asgerf

unified/ql/test/library-tests/dataflow/accessors_local.swift

@@ -92,3 +92,17 @@ func t11() {
     }
     p.0 = source("t11.1")
 }
+
+func t12() {
+    struct S {
+        var field: String = "safe"
+        mutating func mutate() { field = source("t12.1") }
+    }
+    var p: S {
+        get { S() }
+        set { sink(newValue.field) }  // $ MISSING: hasValueFlow=t12.1
+    }
+    // TODO: test fails because the call to 'mutate' is not yet resolved
+    // At the time of writing, the test passes if the call graph is manually patched
+    p.mutate()
+}