Remove forward-compatibility promise and all reserved & private syntax (#883)

* Remove forwards compatibility from stability guarantee

* Drop reserved statements and expressions

* Drop private-use annotations

* Update tests

* Clarify that deprecation is not removal

Author: eemeli

spec/README.md

@@ -90,16 +90,7 @@ Updates to this specification MUST NOT specify the use of a fallback value for a
 that previously did not specify a fallback value.
 
 Updates to this specification will not change the syntactical meaning
-of any syntax defined in this specification except for that syntax marked as
-"reserved for future standardization".
-
-Updates to this specification will not assign any meaning to or change the syntactical 
-requirements for any private-use annotation.
-
-Updates to this specification will not remove any reserved keywords or sigils.
-
-Updates to this specification will not add any additional Unicode code points to 
-those in `reserved-annotation-start`.
+of any syntax defined in this specification.
 
 Updates to this specification will not remove any functions defined in the default registry.
 
@@ -114,13 +105,6 @@ defined in the default registry.
 > differences in implementation or changes to locale data
 > (such as due to the release of new CLDR versions).
 
-Updates to this specification will not introduce message syntax that,
-when parsed according to earlier versions of this specification,
-would produce syntax or data model errors.
-Messages that use syntax introduced in a future version of this specification
-could produce resolution or message function errors
-when formatted according to an earlier version of this specification.
-
 Updates to this specification will only reserve, define, or require
 function names or function option names
 consisting of characters in the ranges a-z, A-Z, and 0-9.
@@ -137,29 +121,19 @@ based on this version being invalid.
 
 > For example, existing interfaces or fields will not be removed.
 
-Future versions of this specification will not introduce syntax that cannot be
-represented by this version of the data model.
-
-> For example, a future version could introduce a new keyword.
-> The future version's data model would provide an interface for that keyword
-> while this version of the data model would parse the value into
-> the interface `UnsupportedStatement`.
-> Both data models would be "valid" in their context,
-> but this version's would be missing any functionality for the new statement type.
-
 > [!IMPORTANT]
 > This stability policy allows any of the following, non-exhaustive list, of changes
 > in future versions of this specification:
+> - Future versions may define new syntax and structures
+>   that would not be supported by this version of the specification.
 > - Future versions may add additional structure or meaning to existing syntax.
 > - Future versions may define new keywords.
-> - Future versions may define annotations that use portions of the `reserved-annotation`
->   syntax.
 > - Future versions may make previously invalid messages valid.
 > - Future versions may define additional functions in the default registry
 >   or may reserve the names of functions for the purposes of interoperability.
 > - Future versions may define additional options to existing functions.
 > - Future versions may define additional option values for existing options.
-> - Future versions may deprecate functions, options, or option values.
+> - Future versions may deprecate (but not remove) keywords, functions, options, or option values.
 > - Future versions of this specification may introduce changes
 >   to the data model that would result in future data model representations
 >   not being valid for implementations of this version of the data model.

spec/data-model/README.md

@@ -17,11 +17,10 @@ Implementations that expose APIs supporting the production, consumption, or tran
 _message_ as a data structure are encouraged to use this data model.
 
 This data model provides these capabilities:
-- any MessageFormat 2 message (including future versions)
-  can be parsed into this representation
+- any MessageFormat 2.0 message can be parsed into this representation
 - this data model representation can be serialized as a well-formed
-MessageFormat 2 message
-- parsing a MessageFormat 2 message into a data model representation
+MessageFormat 2.0 message
+- parsing a MessageFormat 2.0 message into a data model representation
   and then serializing it results in an equivalently functional message
 
 This data model might also be used to:
@@ -98,21 +97,8 @@ The `name` does not include the initial `$` of the _variable_.
 The `name` of an `InputDeclaration` MUST be the same
 as the `name` in the `VariableRef` of its `VariableExpression` `value`.
 
-An `UnsupportedStatement` represents a statement not supported by the implementation.
-Its `keyword` is a non-empty string name (i.e. not including the initial `.`).
-If not empty, the `body` is the "raw" value (i.e. escape sequences are not processed)
-starting after the keyword and up to the first _expression_,
-not including leading or trailing whitespace.
-The non-empty `expressions` correspond to the trailing _expressions_ of the _reserved statement_.
-
-> [!NOTE]
-> Be aware that future versions of this specification
-> might assign meaning to _reserved statement_ values.
-> This would result in new interfaces being added to
-> this data model.
-
 ```ts
-type Declaration = InputDeclaration | LocalDeclaration | UnsupportedStatement;
+type Declaration = InputDeclaration | LocalDeclaration;
 
 interface InputDeclaration {
   type: "input";
@@ -125,13 +111,6 @@ interface LocalDeclaration {
   name: string;
   value: Expression;
 }
-
-interface UnsupportedStatement {
-  type: "unsupported-statement";
-  keyword: string;
-  body?: string;
-  expressions: Expression[];
-}
 ```
 
 In a `SelectMessage`,
@@ -173,34 +152,26 @@ type Pattern = Array<string | Expression | Markup>;
 type Expression =
   | LiteralExpression
   | VariableExpression
-  | FunctionExpression
-  | UnsupportedExpression;
+  | FunctionExpression;
 
 interface LiteralExpression {
   type: "expression";
   arg: Literal;
-  annotation?: FunctionAnnotation | UnsupportedAnnotation;
+  function?: FunctionRef;
   attributes: Attributes;
 }
 
 interface VariableExpression {
   type: "expression";
   arg: VariableRef;
-  annotation?: FunctionAnnotation | UnsupportedAnnotation;
+  function?: FunctionRef;
   attributes: Attributes;
 }
 
 interface FunctionExpression {
   type: "expression";
   arg?: never;
-  annotation: FunctionAnnotation;
-  attributes: Attributes;
-}
-
-interface UnsupportedExpression {
-  type: "expression";
-  arg?: never;
-  annotation: UnsupportedAnnotation;
+  function: FunctionRef;
   attributes: Attributes;
 }
 ```
@@ -209,7 +180,7 @@ interface UnsupportedExpression {
 
 The `Literal` and `VariableRef` correspond to the the _literal_ and _variable_ syntax rules.
 When they are used as the `body` of an `Expression`,
-they represent _expression_ values with no _annotation_.
+they represent _expression_ values with no _function_.
 
 `Literal` represents all literal values, both _quoted literal_ and _unquoted literal_.
 The presence or absence of quotes is not preserved by the data model.
@@ -229,14 +200,14 @@ interface VariableRef {
 }
 ```
 
-A `FunctionAnnotation` represents a _function_ _annotation_.
+A `FunctionRef` represents a _function_.
 The `name` does not include the `:` starting sigil.
 
 `Options` is a key-value mapping containing options,
-and is used to represent the _annotation_ and _markup_ _options_.
+and is used to represent the _function_ and _markup_ _options_.
 
 ```ts
-interface FunctionAnnotation {
+interface FunctionRef {
   type: "function";
   name: string;
   options: Options;
@@ -245,31 +216,13 @@ interface FunctionAnnotation {
 type Options = Map<string, Literal | VariableRef>;
 ```
 
-An `UnsupportedAnnotation` represents a
-_private-use annotation_ not supported by the implementation or a _reserved annotation_.
-The `source` is the "raw" value (i.e. escape sequences are not processed),
-including the starting sigil.
-
-When parsing the syntax of a _message_ that includes a _private-use annotation_
-supported by the implementation,
-the implementation SHOULD represent it in the data model
-using an interface appropriate for the semantics and meaning
-that the implementation attaches to that _annotation_.
-
-```ts
-interface UnsupportedAnnotation {
-  type: "unsupported-annotation";
-  source: string;
-}
-```
-
 ## Markup
 
 A `Markup` object has a `kind` of either `"open"`, `"standalone"`, or `"close"`,
 each corresponding to _open_, _standalone_, and _close_ _markup_.
 The `name` in these does not include the starting sigils `#` and `/` 
 or the ending sigil `/`.
-The `options` for markup use the same key-value mapping as `FunctionAnnotation`.
+The `options` for markup use the same key-value mapping as `FunctionRef`.
 
 ```ts
 interface Markup {

spec/data-model/message.dtd

@@ -1,5 +1,5 @@
 <!ELEMENT message (
-  (declaration | unsupportedStatement)*,
+  (declaration)*,
   (pattern | (selectors,variant+))
 )>
 
@@ -10,12 +10,6 @@
   name NMTOKEN #REQUIRED
 >
 
-<!ELEMENT unsupportedStatement (expression)+>
-<!ATTLIST unsupportedStatement
-  keyword CDATA #REQUIRED
-  body CDATA #IMPLIED
->
-
 <!ELEMENT selectors (expression)+>
 <!ELEMENT variant (key+,pattern)>
 <!ELEMENT key (#PCDATA)>
@@ -24,23 +18,21 @@
 <!ELEMENT pattern (#PCDATA | expression | markup)*>
 
 <!ELEMENT expression (
-  ((literal | variable), (functionAnnotation | unsupportedAnnotation)?, attribute*) |
-  ((functionAnnotation | unsupportedAnnotation), attribute*)
+  ((literal | variable), function?, attribute*) |
+  (function, attribute*)
 )>
 
 <!ELEMENT literal (#PCDATA)>
 
 <!ELEMENT variable (EMPTY)>
 <!ATTLIST variable name NMTOKEN #REQUIRED>
 
-<!ELEMENT functionAnnotation (option)*>
-<!ATTLIST functionAnnotation name NMTOKEN #REQUIRED>
+<!ELEMENT function (option)*>
+<!ATTLIST function name NMTOKEN #REQUIRED>
 
 <!ELEMENT option (literal | variable)>
 <!ATTLIST option name NMTOKEN #REQUIRED>
 
-<!ELEMENT unsupportedAnnotation (#PCDATA)>
-
 <!ELEMENT attribute (literal)?>
 <!ATTLIST attribute name NMTOKEN #REQUIRED>
 

spec/data-model/message.json

@@ -36,7 +36,7 @@
       }
     },
 
-    "function-annotation": {
+    "function": {
       "type": "object",
       "properties": {
         "type": { "const": "function" },
@@ -45,65 +45,17 @@
       },
       "required": ["type", "name"]
     },
-    "unsupported-annotation": {
-      "type": "object",
-      "properties": {
-        "type": { "const": "unsupported-annotation" },
-        "source": { "type": "string" }
-      },
-      "required": ["type", "source"]
-    },
-    "annotation": {
-      "oneOf": [
-        { "$ref": "#/$defs/function-annotation" },
-        { "$ref": "#/$defs/unsupported-annotation" }
-      ]
-    },
-
-    "literal-expression": {
-      "type": "object",
-      "properties": {
-        "type": { "const": "expression" },
-        "arg": { "$ref": "#/$defs/literal" },
-        "annotation": { "$ref": "#/$defs/annotation" },
-        "attributes": { "$ref": "#/$defs/attributes" }
-      },
-      "required": ["type", "arg"]
-    },
-    "variable-expression": {
-      "type": "object",
-      "properties": {
-        "type": { "const": "expression" },
-        "arg": { "$ref": "#/$defs/variable" },
-        "annotation": { "$ref": "#/$defs/annotation" },
-        "attributes": { "$ref": "#/$defs/attributes" }
-      },
-      "required": ["type", "arg"]
-    },
-    "function-expression": {
-      "type": "object",
-      "properties": {
-        "type": { "const": "expression" },
-        "annotation": { "$ref": "#/$defs/function-annotation" },
-        "attributes": { "$ref": "#/$defs/attributes" }
-      },
-      "required": ["type", "annotation"]
-    },
-    "unsupported-expression": {
+    "expression": {
       "type": "object",
       "properties": {
         "type": { "const": "expression" },
-        "annotation": { "$ref": "#/$defs/unsupported-annotation" },
+        "arg": { "$ref": "#/$defs/literal-or-variable" },
+        "function": { "$ref": "#/$defs/function" },
         "attributes": { "$ref": "#/$defs/attributes" }
       },
-      "required": ["type", "annotation"]
-    },
-    "expression": {
       "oneOf": [
-        { "$ref": "#/$defs/literal-expression" },
-        { "$ref": "#/$defs/variable-expression" },
-        { "$ref": "#/$defs/function-expression" },
-        { "$ref": "#/$defs/unsupported-expression" }
+        { "required": ["type", "arg"] },
+        { "required": ["type", "function"] }
       ]
     },
 
@@ -148,26 +100,12 @@
       },
       "required": ["type", "name", "value"]
     },
-    "unsupported-statement": {
-      "type": "object",
-      "properties": {
-        "type": { "const": "unsupported-statement" },
-        "keyword": { "type": "string" },
-        "body": { "type": "string" },
-        "expressions": {
-          "type": "array",
-          "items": { "$ref": "#/$defs/expression" }
-        }
-      },
-      "required": ["type", "keyword", "expressions"]
-    },
     "declarations": {
       "type": "array",
       "items": {
         "oneOf": [
           { "$ref": "#/$defs/input-declaration" },
-          { "$ref": "#/$defs/local-declaration" },
-          { "$ref": "#/$defs/unsupported-statement" }
+          { "$ref": "#/$defs/local-declaration" }
         ]
       }
     },