Function _ValidateClauseOrder

src/ast/ast_validations.c:1930–1986

In any given query scope, reading clauses (MATCH, UNWIND, and InQueryCall) * cannot follow updating clauses (CREATE, MERGE, DELETE, SET, REMOVE, FOREACH). * https://s3.amazonaws.com/artifacts.opencypher.org/railroad/SinglePartQuery.html * Additionally, a MATCH clause cannot follow an OPTIONAL MATCH clause. */

 * https://s3.amazonaws.com/artifacts.opencypher.org/railroad/SinglePartQuery.html
 * Additionally, a MATCH clause cannot follow an OPTIONAL MATCH clause. */
static AST_Validation _ValidateClauseOrder
(
	const AST *ast  // ast
) {
	uint clause_count = cypher_ast_query_nclauses(ast->root);

	bool encountered_optional_match = false;
	bool encountered_updating_clause = false;
	for(uint i = 0; i < clause_count; i ++) {
		const cypher_astnode_t *clause = cypher_ast_query_get_clause(ast->root, i);
		cypher_astnode_type_t type = cypher_astnode_type(clause);
		if(encountered_updating_clause && (type == CYPHER_AST_MATCH          ||
										   type == CYPHER_AST_UNWIND         ||
										   type == CYPHER_AST_CALL           ||
										   type == CYPHER_AST_CALL_SUBQUERY)) {
			ErrorCtx_SetError("A WITH clause is required to introduce %s after an updating clause.",
							  cypher_astnode_typestr(type));
			return AST_INVALID;
		}
		if(type == CYPHER_AST_UNION) {
			encountered_optional_match = false;
			encountered_updating_clause = false;
			continue;
		}
		encountered_updating_clause = (encountered_updating_clause ||
									   _is_updating_clause(clause));

		if(type == CYPHER_AST_MATCH) {
			// Check whether this match is optional
			bool current_clause_is_optional = cypher_ast_match_is_optional(clause);
			// If the current clause is non-optional but we have already
			// encountered an optional match, emit an error
			if(!current_clause_is_optional && encountered_optional_match) {
				ErrorCtx_SetError("A WITH clause is required to introduce a \
MATCH clause after an OPTIONAL MATCH.");
				return AST_INVALID;
			}
			encountered_optional_match |= current_clause_is_optional;
		}

		if(type == CYPHER_AST_WITH) {
			encountered_optional_match = false;
			encountered_updating_clause = false;
		}

		if(type == CYPHER_AST_CALL_SUBQUERY) {
			AST subquery_ast = {
				.root = cypher_ast_call_subquery_get_query(clause)
			};
			if(_ValidateClauseOrder(&subquery_ast) != AST_VALID) {
				return AST_INVALID;
			}
		}
	}

	return AST_VALID;
}