[Tarantool-patches] [PATCH v2 2/3] sql: set an error to diag in sql_execute() on failure

[Leonid Vasiliev <lvasiliev@tarantool.org>]

In SQL, on failure sometimes an error sets to the diag, sometimes not.
And this can dived to situation as in #5537(SEGFAULT).
So, let's set an error to the diag if the result of `sql_execute()`
is a failure and there is no error in the diag.

Part of #5537
---

After some discussion with Sergos, I added a common diag_set
when sql_execute() fails.
I wanted to add such a common error by `diag_add()` if diag
is not empty, but such a change would entail additional correction in tests.
But this patch should be included in the next release, and I want it to
be as small as possible. This patchset is about fixes a crash, not about
refactoring and improvements. For this I will create separate tasks.

 src/box/execute.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/box/execute.c b/src/box/execute.c
index e14da20..87ebb44 100644
--- a/src/box/execute.c
+++ b/src/box/execute.c
@@ -687,8 +687,18 @@ sql_execute(struct sql_stmt *stmt, struct port *port, struct region *region)
 		rc = sql_step(stmt);
 		assert(rc != SQL_ROW && rc != 0);
 	}
-	if (rc != SQL_DONE)
+	if (rc != SQL_DONE) {
+		/*
+		 * In SQL, on failure sometimes an error sets to the diag,
+		 * sometimes not. So, let's set an error to the diag if
+		 * the status is a failure and there is no error in the diag.
+		 */
+		if (diag_is_empty(diag_get())) {
+			diag_set(ClientError, ER_SQL_EXECUTE,
+				 "something went wrong");
+		}
 		return -1;
+	}
 	return 0;
 }
 
-- 
2.7.4