encoding/jsonschema: disallow $schema at non-root for earlier versions

Before 2019-09, the specification says [1]: > The "$schema" keyword SHOULD be used in a root schema. It MUST NOT > appear in subschemas. This change makes us more spec-compliant in that respect. Also change a test case where we were using `$schema` at non-root location. [1]: https://json-schema.org/draft-07/draft-handrews-json-schema-01#rfc.section.7 Signed-off-by: Roger Peppe <[email protected]> Change-Id: If74b25848cc3c334eaaefb46adfe4fe89d0cbb45 Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1202562 Unity-Result: CUE porcuepine <[email protected]> Reviewed-by: Daniel Martí <[email protected]> TryBot-Result: CUEcueckoo <[email protected]>
cue-lang · Oct 15, 2024 · 2c6ed18 · 2c6ed18
1 parent 4543183
commit 2c6ed18
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Showing 4 changed files with 28 additions and 2 deletions.
diff --git a/encoding/jsonschema/constraints_meta.go b/encoding/jsonschema/constraints_meta.go
@@ -50,6 +50,12 @@ func constraintID(key string, n cue.Value, s *state) {
 // constraintSchema implements $schema, which
 // identifies this as a JSON schema and specifies its version.
 func constraintSchema(key string, n cue.Value, s *state) {
+	if !s.isRoot && !vfrom(VersionDraft2019_09).contains(s.schemaVersion) {
+		// Before 2019-09, the $schema keyword was not allowed
+		// to appear anywhere but the root.
+		s.errf(n, "$schema can only appear at the root in JSON Schema version %v", s.schemaVersion)
+		return
+	}
 	str, ok := s.strValue(n)
 	if !ok {
 		// If there's no $schema value, use the default.

diff --git a/encoding/jsonschema/decode.go b/encoding/jsonschema/decode.go
@@ -115,6 +115,7 @@ func (d *decoder) schema(ref []ast.Label, v cue.Value) (a []ast.Decl) {
 	root := state{
 		decoder:       d,
 		schemaVersion: d.cfg.DefaultVersion,
+		isRoot:        true,
 	}
 
 	var name ast.Label
@@ -415,6 +416,10 @@ type state struct {
 	// to $ref.
 	hasRefKeyword bool
 
+	// isRoot holds whether this state is at the root
+	// of the schema.
+	isRoot bool
+
 	minContains *uint64
 	maxContains *uint64
 
@@ -709,6 +714,7 @@ func (s0 *state) schemaState(n cue.Value, types cue.Kind, idRef []label) (ast.Ex
 		knownTypes:    allTypes,
 		idRef:         idRef,
 		pos:           n,
+		isRoot:        s0.isRoot && n == s0.pos,
 	}
 	if n.Kind() == cue.BoolKind {
 		if vfrom(VersionDraft6).contains(s.schemaVersion) {

diff --git a/encoding/jsonschema/testdata/txtar/id_in_oneOf.txtar b/encoding/jsonschema/testdata/txtar/id_in_oneOf.txtar
@@ -4,12 +4,10 @@
   "$id": "https://test.example/foo",
   "oneOf": [
       {
-          "$schema": "http://json-schema.org/draft-07/schema#",
           "$id": "https://1.test.example/string",
           "type": "string"
       },
       {
-          "$schema": "http://json-schema.org/draft-07/schema#",
           "$id": "https://2.test.example/object",
           "type": "object"
       }

diff --git a/encoding/jsonschema/testdata/txtar/schema_not_at_root.txtar b/encoding/jsonschema/testdata/txtar/schema_not_at_root.txtar
@@ -0,0 +1,16 @@
+-- schema.json --
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "https://test.example/foo",
+  "oneOf": [
+      {
+          "$schema": "http://json-schema.org/draft-07/schema#",
+          "type": "string"
+      }
+  ]
+}
+
+-- out/decode/extract --
+ERROR:
+$schema can only appear at the root in JSON Schema version http://json-schema.org/draft-07/schema#:
+    schema.json:6:11