encoding/jsonschema: always allow x- keywords

The OpenAPI specification explicitly allows "x-"-prefixed keywords and
JSON Schema allows all unknown keywords, so it seems reasonable to
always allow them, as the `StrictKeywords` flag is more oriented towards
finding misspelled keywords than explicitly "out-of-spec" keywords.

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: Iaa287b25faeb3cfc03225b06b97547a949026ba7
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1201112
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: rogpeppe

encoding/jsonschema/decode.go

@@ -699,6 +699,13 @@ func (s *state) schemaState(n cue.Value, types cue.Kind, idRef []label, isLogica
 	// do multiple passes over the constraints to ensure they are done in order.
 	for pass := 0; pass < numPhases; pass++ {
 		state.processMap(n, func(key string, value cue.Value) {
+			if strings.HasPrefix(key, "x-") {
+				// A keyword starting with a leading x- is clearly
+				// not intended to be a valid keyword, and is explicitly
+				// allowed by OpenAPI. It seems reasonable that
+				// this is not an error even with StrictKeywords enabled.
+				return
+			}
 			// Convert each constraint into a either a value or a functor.
 			c := constraintMap[key]
 			if c == nil {

encoding/jsonschema/testdata/txtar/strictkeywords.txtar

@@ -1,10 +1,15 @@
 #strictKeywords
+
+Note: x-bar does _not_ cause an error even with StrictKeywords
+enabled.
+
 -- schema.json --
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "type": "number",
   "$dynamicAnchor": "bar",
-  "foo": true
+  "foo": true,
+  "x-bar": true
 }
 -- out/decode/extract --
 ERROR: