Add variants to interfaces as well

Author: delvedor

specification/compiler/model/build-model.ts

@@ -50,7 +50,8 @@ import {
   modelProperty,
   modelType,
   modelTypeAlias,
-  parseVariantNameTag
+  parseVariantNameTag,
+  parseVariantsTag
 } from './utils'
 
 const specsFolder = join(__dirname, '..', '..', 'specs')
@@ -263,6 +264,12 @@ function compileClassOrInterfaceDeclaration (declaration: ClassDeclaration | Int
       type.variantName = variant
     }
 
+    const variants = parseVariantsTag(declaration.getJsDocs())
+    if (variants != null) {
+      assert(variants.kind === 'container', 'Interfaces can only use `container` vairant kind')
+      type.variants = variants
+    }
+
     for (const member of declaration.getMembers()) {
       // Any property definition
       assert(