Add support for mixin syntax

[tobie]

Hey,

We recently changed the WebIDL syntax to add support for mixins. We also added CI tooling to make sure the grammar stayed LL(1), and fixed a couple of issues in the process.

Here's an indicative diff of the recent grammar changes, but please do refer to the IDL index section in the spec for details:

--- (old)
+++ (new)
@@ -3,17 +3,13 @@
     ε
 
 Definition ::
-    CallbackOrInterface
+    CallbackOrInterfaceOrMixin
     Namespace
     Partial
     Dictionary
     Enum
     Typedef
-    ImplementsStatement
-
-CallbackOrInterface ::
-    callback CallbackRestOrInterface
-    Interface
+    IncludesStatement
 
 ArgumentNameKeyword ::
     attribute
@@ -23,7 +19,7 @@
     dictionary
     enum
     getter
-    implements
+    includes
     inherit
     interface
     iterable
@@ -38,23 +34,35 @@
     typedef
     unrestricted
 
+CallbackOrInterfaceOrMixin ::
+    callback CallbackRestOrInterface
+    interface InterfaceOrMixin
+
 CallbackRestOrInterface ::
     CallbackRest
-    Interface
+    interface InterfaceRest
+
+InterfaceOrMixin ::
+    InterfaceRest
+    MixinRest
 
-Interface ::
-    interface identifier Inheritance { InterfaceMembers } ;
+InterfaceRest ::
+    identifier Inheritance { InterfaceMembers } ;
 
 Partial ::
     partial PartialDefinition
 
 PartialDefinition ::
-    PartialInterface
+    interface PartialInterfaceOrPartialMixin
     PartialDictionary
     Namespace
 
-PartialInterface ::
-    interface identifier { InterfaceMembers } ;
+PartialInterfaceOrPartialMixin ::
+    PartialInterfaceRest
+    MixinRest
+
+PartialInterfaceRest ::
+    identifier { InterfaceMembers } ;
 
 InterfaceMembers ::
     ExtendedAttributeList InterfaceMember InterfaceMembers
@@ -75,6 +83,22 @@
     : identifier
     ε
 
+MixinRest ::
+    mixin identifier { MixinMembers } ;
+
+MixinMembers ::
+    ExtendedAttributeList MixinMember MixinMembers
+    ε
+
+MixinMember ::
+    Const
+    RegularOperation
+    Stringifier
+    ReadOnly AttributeRest
+
+IncludesStatement ::
+    identifier includes identifier ;
+
 Const ::
     const ConstType identifier = ConstValue ;
 
@@ -130,11 +154,14 @@
     [ ]
 
 Operation ::
-    ReturnType OperationRest
+    RegularOperation
     SpecialOperation
 
+RegularOperation ::
+    ReturnType OperationRest
+
 SpecialOperation ::
-    Special Specials ReturnType OperationRest
+    Special Specials RegularOperation
 
 Specials ::
     Special Specials
@@ -161,8 +188,11 @@
     ε
 
 Argument ::
-    ExtendedAttributeList optional TypeWithExtendedAttributes ArgumentName Default
-    ExtendedAttributeList Type Ellipsis ArgumentName
+    ExtendedAttributeList ArgumentRest
+
+ArgumentRest ::
+    optional TypeWithExtendedAttributes ArgumentName Default
+    Type Ellipsis ArgumentName
 
 ArgumentName ::
     ArgumentNameKeyword
@@ -181,7 +211,7 @@
 
 StringifierRest ::
     ReadOnly AttributeRest
-    ReturnType OperationRest
+    RegularOperation
     ;
 
 StaticMember ::
@@ -189,7 +219,7 @@
 
 StaticMemberRest ::
     ReadOnly AttributeRest
-    ReturnType OperationRest
+    RegularOperation
 
 Iterable ::
     iterable < TypeWithExtendedAttributes OptionalType > ;
@@ -218,7 +248,7 @@
     ε
 
 NamespaceMember ::
-    ReturnType OperationRest
+    RegularOperation
     readonly AttributeRest
 
 Dictionary ::
@@ -229,8 +259,11 @@
     ε
 
 DictionaryMember ::
-    ExtendedAttributeList required TypeWithExtendedAttributes identifier Default ;
-    ExtendedAttributeList Type identifier Default ;
+    ExtendedAttributeList DictionaryMemberRest
+
+DictionaryMemberRest ::
+    required TypeWithExtendedAttributes identifier Default ;
+    Type identifier Default ;
 
 PartialDictionary ::
     dictionary identifier { DictionaryMembers } ;
@@ -259,16 +292,12 @@
 Typedef ::
     typedef TypeWithExtendedAttributes identifier ;
 
-ImplementsStatement ::
-    identifier implements identifier ;
-
 Type ::
     SingleType
     UnionType Null
 
 TypeWithExtendedAttributes ::
-    ExtendedAttributeList SingleType
-    ExtendedAttributeList UnionType Null
+    ExtendedAttributeList Type
 
 SingleType ::
     NonAnyType

Let me know if there's anything I can do to help!

---

Tracked in: whatwg/webidl#472 | Original pull-request: whatwg/webidl#433

[domenic]

Ping; this is blocking a lot of specs that would like to update :)

[plinss]

Ping @tabatkins to upstream into Bikeshed