Add spec version to Libdoc JSON specs (and schema).

Part of #4281.

doc/schema/libdoc.json

@@ -1,7 +1,11 @@
 {
   "title": "Libdoc",
+  "description": "Libdoc JSON spec file schema.\n\nCompatible with JSON Schema Draft 2020-12.",
   "type": "object",
   "properties": {
+    "specversion": {
+      "$ref": "#/definitions/SpecVersion"
+    },
     "name": {
       "title": "Name",
       "type": "string"
@@ -75,6 +79,7 @@
     }
   },
   "required": [
+    "specversion",
     "name",
     "doc",
     "version",
@@ -91,6 +96,14 @@
   ],
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "definitions": {
+    "SpecVersion": {
+      "title": "SpecVersion",
+      "description": "Version of the spec.",
+      "enum": [
+        1
+      ],
+      "type": "integer"
+    },
     "DocumentationType": {
       "title": "DocumentationType",
       "description": "Type of the doc: LIBRARY or RESOURCE.",

doc/schema/libdoc_json_schema.py

@@ -8,6 +8,11 @@
 from pydantic import BaseModel, Field, PositiveInt
 
 
+class SpecVersion(int, Enum):
+    """Version of the spec."""
+    VERSION = 1
+
+
 class DocumentationType(str, Enum):
     """Type of the doc: LIBRARY or RESOURCE."""
     LIBRARY = 'LIBRARY'
@@ -105,7 +110,11 @@ class TypeDoc(BaseModel):
 
 
 class Libdoc(BaseModel):
-    #specversion
+    """Libdoc JSON spec file schema.
+
+    Compatible with JSON Schema Draft 2020-12.
+    """
+    specversion: SpecVersion
     name: str
     doc: str
     version: str

src/robot/libdocpkg/model.py

@@ -110,6 +110,7 @@ def convert_docs_to_html(self):
 
     def to_dictionary(self):
         return {
+            'specversion': 1,
             'name': self.name,
             'doc': self.doc,
             'version': self.version,