Add Dart.g support for class modifiers

This CL adds/changes the specification grammar to support the upcoming 'class modifiers' feature. Also, it changes the rule about `superclass` to agree with the language specification (it is easy to see that it derives the same set of programs). Also introduces a non-terminal `otherIdentifier` listing those words which are not reserved, not built-in, but are still explicitly mentioned in grammar (e.g., `show`, `on`, and others). This is safer than maintaining a repeated list of words multiple places in the grammar.

Change-Id: I23dc303f9f9a06a665e19f375fe23378042434c2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/283183
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: Erik Ernst <eernst@google.com>

tools/spec_parser/Dart.g

@@ -4,6 +4,12 @@
 
 // CHANGES:
 //
+// v0.30 Add support for the class modifiers `sealed`, `final`, `base`,
+// `interface`, and for `mixin class` declarations. Also add support for
+// unnamed libraries (`library;`). Introduce `otherIdentifier` to help
+// maintaining consistency when the grammar is modified to mention any words
+// that weren't previously mentioned, yet are not reserved or built-in.
+//
 // v0.29 Add an alternative in the `primary` rule to enable method invocations
 // of the form `super(...)` and `super<...>(...)`. This was added to the
 // language specification in May 21, b26e7287c318c0112610fe8b7e175289792dfde2,
@@ -361,13 +367,24 @@ typeWithParameters
     ;
 
 classDeclaration
-    :    ABSTRACT? CLASS typeWithParameters superclass? mixins? interfaces?
-         LBRACE (metadata classMemberDefinition)* RBRACE
-    |    ABSTRACT? CLASS mixinApplicationClass
+    :    (classModifiers | mixinClassModifiers)
+         CLASS typeWithParameters superclass? interfaces?
+         LBRACE (metadata classMemberDeclaration)* RBRACE
+    |    classModifiers CLASS mixinApplicationClass
+    ;
+
+classModifiers
+    :    SEALED
+    |    ABSTRACT? (BASE | INTERFACE | FINAL)?
+    ;
+
+mixinClassModifiers
+    :    ABSTRACT? BASE? MIXIN
     ;
 
 superclass
-    :    EXTENDS typeNotVoidNotFunction
+    :    EXTENDS typeNotVoidNotFunction mixins?
+    |    mixins
     ;
 
 mixins
@@ -378,7 +395,7 @@ interfaces
     :    IMPLEMENTS typeNotVoidNotFunctionList
     ;
 
-classMemberDefinition
+classMemberDeclaration
     :    methodSignature functionBody
     |    declaration ';'
     ;
@@ -388,14 +405,21 @@ mixinApplicationClass
     ;
 
 mixinDeclaration
-    :    MIXIN typeIdentifier typeParameters?
+    :    mixinModifier? MIXIN typeIdentifier typeParameters?
          (ON typeNotVoidNotFunctionList)? interfaces?
-         LBRACE (metadata mixinMemberDefinition)* RBRACE
+         LBRACE (metadata mixinMemberDeclaration)* RBRACE
     ;
 
-// TODO: We will probably want to make this more strict.
-mixinMemberDefinition
-    :    classMemberDefinition
+mixinModifier
+    :    SEALED
+    |    BASE
+    |    INTERFACE
+    |    FINAL
+    ;
+
+// TODO: We might want to make this more strict.
+mixinMemberDeclaration
+    :    classMemberDeclaration
     ;
 
 extensionDeclaration
@@ -405,7 +429,7 @@ extensionDeclaration
 
 // TODO: We might want to make this more strict.
 extensionMemberDefinition
-    :    classMemberDefinition
+    :    classMemberDeclaration
     ;
 
 methodSignature
@@ -533,7 +557,7 @@ mixinApplication
 enumType
     :    ENUM typeIdentifier typeParameters? mixins? interfaces? LBRACE
          enumEntry (',' enumEntry)* (',')?
-         (';' (metadata classMemberDefinition)*)?
+         (';' (metadata classMemberDeclaration)*)?
          RBRACE
     ;
 
@@ -976,12 +1000,7 @@ assignableSelector
 identifierNotFUNCTION
     :    IDENTIFIER
     |    builtInIdentifier
-    |    ASYNC // Not a built-in identifier.
-    |    HIDE // Not a built-in identifier.
-    |    OF // Not a built-in identifier.
-    |    ON // Not a built-in identifier.
-    |    SHOW // Not a built-in identifier.
-    |    SYNC // Not a built-in identifier.
+    |    otherIdentifier
     |    { asyncEtcPredicate(getCurrentToken().getType()) }? (AWAIT|YIELD)
     ;
 
@@ -998,12 +1017,7 @@ qualifiedName
 typeIdentifier
     :    IDENTIFIER
     |    DYNAMIC // Built-in identifier that can be used as a type.
-    |    ASYNC // Not a built-in identifier.
-    |    HIDE // Not a built-in identifier.
-    |    OF // Not a built-in identifier.
-    |    ON // Not a built-in identifier.
-    |    SHOW // Not a built-in identifier.
-    |    SYNC // Not a built-in identifier.
+    |    otherIdentifier // Occur in grammar rules, are not built-in.
     |    { asyncEtcPredicate(getCurrentToken().getType()) }? (AWAIT|YIELD)
     ;
 
@@ -1319,7 +1333,7 @@ assertion
     ;
 
 libraryName
-    :    metadata LIBRARY dottedIdentifierList ';'
+    :    metadata LIBRARY dottedIdentifierList? ';'
     ;
 
 dottedIdentifierList
@@ -1602,6 +1616,18 @@ builtInIdentifier
     |    TYPEDEF
     ;
 
+otherIdentifier
+    :    ASYNC
+    |    BASE
+    |    HIDE
+    |    OF
+    |    ON
+    |    SEALED
+    |    SHOW
+    |    SYNC
+    |    WHEN
+    ;
+
 // ---------------------------------------- Lexer rules.
 
 fragment
@@ -1627,7 +1653,7 @@ HEX_DIGIT
     |    DIGIT
     ;
 
-// Reserved words.
+// Reserved words (if updated, update `reservedWord` as well).
 
 ASSERT
     :    'assert'
@@ -1761,7 +1787,7 @@ WITH
     :    'with'
     ;
 
-// Built-in identifiers.
+// Built-in identifiers (if updated, update `builtInIdentifier` as well).
 
 ABSTRACT
     :    'abstract'
@@ -1865,12 +1891,16 @@ YIELD
     :    'yield'
     ;
 
-// Other words used in the grammar.
+// Other words used in the grammar (if updated, update `otherIdentifier`, too).
 
 ASYNC
     :    'async'
     ;
 
+BASE
+    :    'base'
+    ;
+
 HIDE
     :    'hide'
     ;
@@ -1883,6 +1913,10 @@ ON
     :    'on'
     ;
 
+SEALED
+    :    'sealed'
+    ;
+
 SHOW
     :    'show'
     ;