Revert "Update v1/topdown/graphql.go"

v1/topdown/graphql.go:582:17: cannot use schemaAST (variable of interface type "github.com/open-policy-agent/opa/v1/ast".Value) as *"github.com/open-policy-agent/opa/internal/gqlparser/ast".SchemaDocument value in return statement

This reverts commit 0f34a78.

Author: Rob Myers

Diff for: v1/topdown/graphql.go

@@ -576,15 +576,20 @@ func cacheGetSchema(bctx BuiltinContext, operands []*ast.Term) (string, *gqlast.
 // Returns the cache key and a SchemaDocument if this key already exists in the cache
 // Note: the SchemaDocument is not a validated Schema
 func cacheGetSchemaDoc(bctx BuiltinContext, operands []*ast.Term) (string, *gqlast.SchemaDocument) {
-	if key, keyOk := cacheKeyWithPrefix(bctx, operands, "gql_schema_ast"); keyOk {
+	var key string
+	var schemaDoc *gqlast.SchemaDocument
+
+	if k, keyOk := cacheKeyWithPrefix(bctx, operands, "gql_schema_doc"); keyOk {
+		key = k
 		if val, ok := bctx.InterQueryBuiltinValueCache.Get(ast.StringTerm(key).Value); ok {
-			if schemaAST, isAstValue := val.(ast.Value); isAstValue {
-				return key, schemaAST
+			var isSchema bool
+			schemaDoc, isSchema = val.(*gqlast.SchemaDocument)
+			if !isSchema {
+				return key, nil
 			}
 		}
-		return key, nil
 	}
-	return "", nil
+	return key, schemaDoc
 }
 
 // Returns the cache key and a SchemaDocument if this key already exists in the cache