C# 7.x: Allow field-targeted attributes on auto-property declarations

standard/attributes.md

@@ -275,7 +275,7 @@ No other values for *global_attribute_target* are allowed.
 The standardized *attribute_target* names are `event`, `field`, `method`, `param`, `property`, `return`, `type`, and `typevar`. These target names shall only be used in the following contexts:
 
 - `event` — an event.
-- `field` — a field. A field-like event (i.e., one without accessors) can also have an attribute with this target.
+- `field` — a field. A field-like event (i.e., one without accessors) ([§14.8.2](classes.md#1482-field-like-events)) and an automatically implemented property ([§14.7.4](classes.md#1474-automatically-implemented-properties)) can also have an attribute with this target.
 - `method` — a constructor, finalizer, method, operator, property get and set accessors, indexer get and set accessors, and event add and remove accessors. A field-like event (i.e., one without accessors) can also have an attribute with this target.
 - `param` — a property set accessor, an indexer set accessor, event add and remove accessors, and a parameter in a constructor, method, and operator.
 - `property` — a property and an indexer.
@@ -300,6 +300,8 @@ Certain contexts permit the specification of an attribute on more than one targe
 - For an attribute specified on a set accessor for a property or indexer declaration the default target is the associated method. Otherwise when the *attribute_target* is equal to:
   - `method` — the target is the associated method
   - `param` — the target is the lone implicit parameter
+- For an attribute on an automatically implemented property declaration the default target is the property. Otherwise when the *attribute_target* is equal to:
+  - `field` — the target is the compiler-generated backing field for the property
 - For an attribute specified on an event declaration that omits *event_accessor_declarations* the default target is the event declaration. Otherwise when the *attribute_target* is equal to:
   - `event` — the target is the event declaration
   - `field` — the target is the field

standard/classes.md

@@ -3447,6 +3447,37 @@ An auto-property may optionally have a *property_initializer*, which is applied
 >
 > *end example*
 
+Although the backing field is hidden, that field may have field-targeted attributes applied directly to it via the automatically implemented property's *property_declaration* ([§14.7.1](classes.md#1471-general)).
+
+> *Example*: The following code
+>
+> ```csharp
+> [Serializable]
+> public class Foo
+> {
+>     [field: NonSerialized]
+>     public string MySecret { get; set; }
+> }
+> ```
+>
+> results in the field-targeted attribute `NonSerialized` being applied to the compiler-generated backing field, as if the code had been written as follows:
+>
+> ```csharp
+> [Serializable]
+> public class Foo
+> {
+>     [NonSerialized]
+>     private string _mySecretBackingField;
+>     public string MySecret
+>     {
+>         get { return _mySecretBackingField; }
+>         set { _mySecretBackingField = value; }
+>     }
+> }
+> ```
+>
+> *end example*
+
 ### 14.7.5 Accessibility
 
 If an accessor has an *accessor_modifier*, the accessibility domain ([§7.5.3](basic-concepts.md#753-accessibility-domains)) of the accessor is determined using the declared accessibility of the *accessor_modifier*. If an accessor does not have an *accessor_modifier*, the accessibility domain of the accessor is determined from the declared accessibility of the property or indexer.