Improve error message when compiling a $ref inside an unknown keyword

DEPENDENCIES

@@ -1,4 +1,4 @@
 vendorpull https://github.com/sourcemeta/vendorpull dea311b5bfb53b6926a4140267959ae334d3ecf4
 noa https://github.com/sourcemeta/noa 7e26abce7a4e31e86a16ef2851702a56773ca527
-jsontoolkit https://github.com/sourcemeta/jsontoolkit 2b44aee9b2be18a03b375c0b1f15c7623db8b922
+jsontoolkit https://github.com/sourcemeta/jsontoolkit e7a8f35b0b85cd87b5fa587b2ae767ed939a0b4d
 hydra https://github.com/sourcemeta/hydra 3c53d3fdef79e9ba603d48470a508cc45472a0dc

test/CMakeLists.txt

@@ -140,6 +140,7 @@ add_jsonschema_test_unix(compile/pass_2)
 add_jsonschema_test_unix(compile/fail_no_schema)
 add_jsonschema_test_unix(compile/fail_schema_invalid_json)
 add_jsonschema_test_unix(compile/fail_unknown_metaschema)
+add_jsonschema_test_unix(compile/fail_ref_from_unknown_keyword)
 
 # Identify
 add_jsonschema_test_unix(identify/fail_resolve_from_no_match)

test/compile/fail_ref_from_unknown_keyword.sh

@@ -0,0 +1,35 @@
+#!/bin/sh
+
+set -o errexit
+set -o nounset
+
+TMP="$(mktemp -d)"
+clean() { rm -rf "$TMP"; }
+trap clean EXIT
+
+cat << 'EOF' > "$TMP/schema.json"
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "properties": {
+    "foo": { "$ref": "#/$defs/bar" },
+    "baz": { "type": "string" }
+  },
+  "$defs": {
+    "bar": {
+      "$ref": "#/properties/baz"
+    }
+  }
+}
+EOF
+
+"$1" compile "$TMP/schema.json" 2>"$TMP/stderr.txt" \
+  && CODE="$?" || CODE="$?"
+test "$CODE" = "1" || exit 1
+
+cat << 'EOF' > "$TMP/expected.txt"
+error: The schema location is inside of an unknown keyword
+  #/properties/baz
+    at schema location "/$defs/bar/$ref"
+EOF
+
+diff "$TMP/stderr.txt" "$TMP/expected.txt"