[form-builder] Fix issue with recursive string field lookup for refer…

…ence search

packages/@sanity/form-builder/src/sanity/inputs/client-adapters/reference.js

@@ -15,37 +15,42 @@ function wrapIn(chars = '') {
 
 const wrapInParens = wrapIn('()')
 
-const stringFields = Symbol('__cachedStringFields')
+const stringFieldsSymbol = Symbol('__cachedStringFields')
 
 function getCachedStringFieldPaths(type, maxDepth) {
-  if (!type[stringFields]) {
-    type[stringFields] = getStringFieldPaths(type, maxDepth)
+  if (!type[stringFieldsSymbol]) {
+    type[stringFieldsSymbol] = getStringFieldPaths(type, maxDepth)
   }
-  return type[stringFields]
+  return type[stringFieldsSymbol]
 }
 
-function getStringFieldPaths(type, maxDepth = 2) {
+function reduceType(type, reducer, accumulator, path = [], maxDepth = 10) {
   if (maxDepth < 0) {
-    return []
+    return accumulator
   }
-  return (type.fields || [])
-    .map(field => {
-      if (field.type.jsonType === 'string') {
-        return [[field.name]]
-      }
-      if (field.type.jsonType === 'object') {
-        return getCachedStringFieldPaths(field.type, maxDepth - 1).map(path => [field.name, ...flatten(path)])
-      }
-      return null
-    })
-    .filter(Boolean)
+  if (Array.isArray(type.fields)) {
+    return type.fields.reduce(
+      (acc, field, index) => reduceType(field.type, reducer, acc, path.concat(field.name), maxDepth - 1),
+      reducer(accumulator, type, path)
+    )
+  }
+  return reducer(accumulator, type, path)
+}
+
+function getStringFieldPaths(type, maxDepth) {
+  const reducer = (accumulator, childType, path) =>
+    (childType.jsonType === 'string'
+      ? [...accumulator, path]
+      : accumulator
+    )
 
+  return reduceType(type, reducer, [], [], maxDepth)
 }
 
 function buildConstraintFromType(type, terms) {
   const typeConstraint = `_type == '${type.name}'`
 
-  const stringFieldPaths = flatten(getCachedStringFieldPaths(type, 2))
+  const stringFieldPaths = getCachedStringFieldPaths(type, 4)
   if (stringFieldPaths.length === 0) {
     return typeConstraint
   }