encoding/jsonschema: support x-kubernetes-embedded-resource

This adds initial support for the "x-kubernetes-embedded-resource"
keyword.

See https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#rawextension

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: Ifdf199380fe24bbd7fcf8df1b5bb87faab4d226a
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1211212
Reviewed-by: Daniel Martí <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: rogpeppe

encoding/jsonschema/constraints.go

@@ -127,7 +127,7 @@ var constraints = []*constraint{
 	p2("uniqueItems", constraintUniqueItems, allVersions|openAPI|k8sCRD),
 	px("writeOnly", constraintTODO, vfrom(VersionDraft7)|openAPI),
 	px("xml", constraintTODO, openAPI),
-	px("x-kubernetes-embedded-resource", constraintTODO, k8sCRD),
+	p1("x-kubernetes-embedded-resource", constraintEmbeddedResource, k8sCRD),
 	p2("x-kubernetes-int-or-string", constraintIntOrString, k8sCRD),
 	px("x-kubernetes-list-map-keys", constraintTODO, k8sCRD),
 	px("x-kubernetes-list-type", constraintTODO, k8sCRD),

encoding/jsonschema/constraints_object.go

@@ -139,13 +139,43 @@ func constraintPatternProperties(key string, n cue.Value, s *state) {
 	})
 }
 
+func constraintEmbeddedResource(key string, n cue.Value, s *state) {
+	// TODO:
+	// - should fail if type has not been specified as "object"
+	// - should fail if neither x-kubernetes-preserve-unknown-fields or properties have been specified
+
+	// Note: this runs in a phase before the properties keyword so
+	// that the embedded expression always comes first in the struct
+	// literal.
+	resourceDefinitionPath := cue.MakePath(cue.Hid("_embeddedResource", "_"))
+	obj := s.object(n)
+
+	// Generate a reference to a shared schema that all embedded resources
+	// can share. If it already exists, that's fine.
+	// TODO add an attribute to make it clear what's going on here
+	// when encoding a CRD from CUE?
+	s.builder.put(resourceDefinitionPath, ast.NewStruct(
+		"apiVersion", token.NOT, ast.NewIdent("string"),
+		"kind", token.NOT, ast.NewIdent("string"),
+		"metadata", token.NOT, ast.NewStruct(&ast.Ellipsis{}),
+	), nil)
+	refExpr, err := s.builder.getRef(resourceDefinitionPath)
+	if err != nil {
+		s.errf(n, `cannot get reference to embedded resource definition: %v`, err)
+	} else {
+		obj.Elts = append(obj.Elts, &ast.EmbedDecl{
+			Expr: refExpr,
+		})
+	}
+	s.allowedTypes &= cue.StructKind
+}
+
 func constraintProperties(key string, n cue.Value, s *state) {
 	obj := s.object(n)
 
 	if n.Kind() != cue.StructKind {
 		s.errf(n, `"properties" expected an object, found %v`, n.Kind())
 	}
-
 	s.processMap(n, func(key string, n cue.Value) {
 		// property?: value
 		name := ast.NewString(key)

encoding/jsonschema/testdata/txtar/crd_embeddedresource.txtar

@@ -0,0 +1,66 @@
+#version: crd
+
+-- schema.json --
+{
+    "apiVersion": "apiextensions.k8s.io/v1",
+    "kind": "CustomResourceDefinition",
+    "metadata": {
+        "name": "myapps.example.com"
+    },
+    "spec": {
+        "group": "example.com",
+        "scope": "Namespaced",
+        "names": {
+            "kind": "MyApp",
+            "singular": "myapp",
+            "plural": "myapps"
+        },
+        "versions": [
+            {
+                "name": "v1",
+                "served": true,
+                "storage": true,
+                "schema": {
+                    "openAPIV3Schema": {
+                        "type": "object",
+                        "properties": {
+                            "r1": {
+                                "type": "object",
+                                "x-kubernetes-embedded-resource": true,
+                                "x-kubernetes-preserve-unknown-fields": true
+                            },
+                            "r2": {
+                                "type": "object",
+                                "x-kubernetes-embedded-resource": true,
+                                "properties": {
+                                    "foo": {
+                                        "type": "string"
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        ]
+    }
+}
+-- out/decode/extract --
+close({
+	r1?: {
+		_embeddedResource
+		...
+	}
+	r2?: close({
+		_embeddedResource
+		foo?: string
+	})
+})
+
+_embeddedResource: {
+	apiVersion!: string
+	kind!:       string
+	metadata!: {
+		...
+	}
+}