Add support for init accessors

standard/attributes.md

@@ -105,9 +105,9 @@ class X : Attribute { ... }
 
 ### 22.2.3 Positional and named parameters
 
-Attribute classes can have ***positional parameter***s and ***named parameter***s. Each public instance constructor for an attribute class defines a valid sequence of positional parameters for that attribute class. Each non-static public read-write field and property for an attribute class defines a named parameter for the attribute class. For a property to define a named parameter, that property shall have both a public get accessor and a public set accessor.
+Attribute classes can have ***positional parameters*** and ***named parameters***. Each public instance constructor for an attribute class defines a valid sequence of positional parameters for that attribute class. Each non-static public read-write field and non-static public read-write or read-init property for an attribute class defines a named parameter for the attribute class. For a property to define a named parameter, that property shall have both a public get accessor and a public set or init accessor.
 
-> *Example*: The following example defines an attribute class named `HelpAttribute` that has one positional parameter, `url`, and one named parameter, `Topic`. Although it is non-static and public, the property `Url` does not define a named parameter, since it is not read-write. Two uses of this attribute are also shown:
+> *Example*: The following example defines an attribute class named `HelpAttribute` that has one positional parameter, `url`, and one named parameter, `Topic`. Although it is non-static and public, the property `Url` does not define a named parameter, since it is not read-write or read-init. Two uses of this attribute are also shown:
 >
 > <!-- Example: {template:"standalone-lib", name:"PositionalAndNamedParameters1", replaceEllipsis:true} -->
 > <!-- Maintenance Note: A version of this type exists in additional-files as "HelpAttribute.cs". As such, certain changes to this type definition might need to be reflected in that file, in which case, *all* examples using that file should be tested. -->
@@ -252,8 +252,8 @@ The standardized *attribute_target* names are `event`, `field`, `method`, `param
 
 - `event` — an event.
 - `field` — a field. A field-like event (i.e., one without accessors) ([§15.8.2](classes.md#1582-field-like-events)) and an automatically implemented property ([§15.7.4](classes.md#1574-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.
+- `method` — a constructor; finalizer; method; operator; property get, set, and init accessors; indexer get, set, and init 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` — property set and init accessors, indexer set and init accessors, event add and remove accessors, and a parameter in a constructor, method, and operator.
 - `property` — a property and an indexer.
 - `return` — a delegate, method, operator, property get accessor, and indexer get accessor.
 - `type` — a delegate, class, struct, enum, and interface.
@@ -273,7 +273,7 @@ Certain contexts permit the specification of an attribute on more than one targe
 - For an attribute on a get accessor declaration 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
   - `return` — the target is the return value
-- 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:
+- For an attribute specified on a set or init 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:
@@ -465,7 +465,7 @@ The compilation of an *attribute* with attribute class `T`, *positional_argumen
 - If `C` does not have public accessibility, then a compile-time error occurs.
 - For each *named_argument* `Arg` in `N`:
   - Let `Name` be the *identifier* of the *named_argument* `Arg`.
-  - `Name` shall identify a non-static read-write public field or property on `T`. If `T` has no such field or property, then a compile-time error occurs.
+  - `Name` shall identify a non-static public read-write field or a non-static public read-write or read-init property on `T`. If `T` has no such field or property, then a compile-time error occurs.
 - If any of the values within *positional_argument_list* `P` or one of the values within *named_argument_list* `N` is of type `System.String` and the value is not well-formed as defined by the Unicode Standard, it is implementation-defined whether the value compiled is equal to the run-time value retrieved ([§22.4.3](attributes.md#2243-run-time-retrieval-of-an-attribute-instance)).
   > *Note*: As an example, a string which contains a high surrogate UTF-16 code unit which isn’t immediately followed by a low surrogate code unit is not well-formed. *end note*
 - Store the following information (for run-time instantiation of the attribute) in the assembly output by the compiler as a result of compiling the program containing the attribute: the attribute class `T`, the instance constructor `C` on `T`, the *positional_argument_list* `P`, the *named_argument_list* `N`, and the associated program entity `E`, with the values resolved completely at compile-time.
@@ -476,7 +476,7 @@ Using the terms defined in [§22.4.2](attributes.md#2242-compilation-of-an-attri
 
 - Follow the run-time processing steps for executing an *object_creation_expression* of the form `new T(P)`, using the instance constructor `C` and values as determined at compile-time. These steps either result in an exception, or produce an instance `O` of `T`.
 - For each *named_argument* `Arg` in `N`, in order:
-  - Let `Name` be the *identifier* of the *named_argument* `Arg`. If `Name` does not identify a non-static public read-write field or property on `O`, then an exception is thrown.
+  - Let `Name` be the *identifier* of the *named_argument* `Arg`. If `Name` does not identify a non-static public read-write field or a non-static public read-write or read-init property on `O`, then an exception is thrown.
   - Let `Value` be the result of evaluating the *attribute_argument_expression* of `Arg`.
   - If `Name` identifies a field on `O`, then set this field to `Value`.
   - Otherwise, Name identifies a property on `O`. Set this property to Value.

standard/basic-concepts.md

@@ -81,7 +81,7 @@ There are several different types of declaration spaces, as described in the fol
 - Each non-partial class, struct, or interface declaration creates a new declaration space. Each partial class, struct, or interface declaration contributes to a declaration space shared by all matching parts in the same program ([§16.2.4](structs.md#1624-partial-modifier)). Names are introduced into this declaration space through *class_member_declaration*s, *struct_member_declaration*s, *interface_member_declaration*s, or *type_parameter*s. Except for overloaded instance constructor declarations and static constructor declarations, a class or struct cannot contain a member declaration with the same name as the class or struct. A class, struct, or interface permits the declaration of overloaded methods and indexers. Furthermore, a class or struct permits the declaration of overloaded instance constructors and operators. For example, a class, struct, or interface may contain multiple method declarations with the same name, provided these method declarations differ in their signature ([§7.6](basic-concepts.md#76-signatures-and-overloading)). Note that base classes do not contribute to the declaration space of a class, and base interfaces do not contribute to the declaration space of an interface. Thus, a derived class or interface is allowed to declare a member with the same name as an inherited member. Such a member is said to ***hide*** the inherited member.
 - Each delegate declaration creates a new declaration space. Names are introduced into this declaration space through parameters (*fixed_parameter*s and *parameter_array*s) and *type_parameter*s.
 - Each enumeration declaration creates a new declaration space. Names are introduced into this declaration space through *enum_member_declarations*.
-- Each method declaration, property declaration, property accessor declaration, indexer declaration, indexer accessor declaration, operator declaration, instance constructor declaration, anonymous function, and local function creates a new declaration space called a ***local variable declaration space***. Names are introduced into this declaration space through parameters (*fixed_parameter*s and *parameter_array*s) and *type_parameter*s. The set accessor for a property or an indexer introduces the name `value` as a parameter. The body of the function member, anonymous function, or local function, if any, is considered to be nested within the local variable declaration space. When a local variable declaration space and a nested local variable declaration space contain elements with the same name, within the scope of the nested local name, the outer local name is hidden ([§7.7.1](basic-concepts.md#771-general)) by the nested local name.
+- Each method declaration, property declaration, property accessor declaration, indexer declaration, indexer accessor declaration, operator declaration, instance constructor declaration, anonymous function, and local function creates a new declaration space called a ***local variable declaration space***. Names are introduced into this declaration space through parameters (*fixed_parameter*s and *parameter_array*s) and *type_parameter*s. The set and init accessors for a property or an indexer introduces the name `value` as a parameter. The body of the function member, anonymous function, or local function, if any, is considered to be nested within the local variable declaration space. When a local variable declaration space and a nested local variable declaration space contain elements with the same name, within the scope of the nested local name, the outer local name is hidden ([§7.7.1](basic-concepts.md#771-general)) by the nested local name.
 - Additional local variable declaration spaces may occur within member declarations, anonymous functions and local functions. Names are introduced into these declaration spaces through *pattern*s, *declaration_expression*s,  *declaration_statement*s and *exception_specifier*s. Local variable declaration spaces may be nested, but it is an error for a local variable declaration space and a nested local variable declaration space to contain elements with the same name. Thus, within a nested declaration space it is not possible to declare a local variable, local function or constant with the same name as a parameter, type parameter, local variable, local function or constant in an enclosing declaration space. It is possible for two declaration spaces to contain elements with the same name as long as neither declaration space contains the other. Local declaration spaces are created by the following constructs:
   - Each *variable_initializer* in a field and property declaration introduces its own local variable declaration space, that is not nested within any other local variable declaration space.
   - The body of a function member, anonymous function, or local function, if any, creates a local variable declaration space that is considered to be nested within the function’s local variable declaration space.