mx_mysql: Remove faulty errno range check

The assertion

    mx_assert_return_minus_errno((unsigned int)(int)error == error, ERANGE);

does not function as intended, as the conditional expression is
optimized away to true by gcc with -O1 and up [1].

While there are alternatives to detect values outside of the range
[0..-INT_MIN] that could not be negated into the range [INT_MIN..0], the
check appears to be unnecessary.  All callers use the MySQL error numbe
for comparison with constants.

This commit removes the helper functions `mx__mysql_errno()` and
`mx__mysql_stmt_errno()` and replaces them with native MySQL calls.

[1]: https://godbolt.org/z/1ajK384Ge

mx_mysql.c

@@ -45,20 +45,6 @@ char *mx_mysql_error(void) {
     return mx_mysql_last_error == NULL ? "no error information" : mx_mysql_last_error;
 }
 
-static int mx__mysql_errno(struct mx_mysql *mysql)
-{
-    unsigned int error;
-
-    mx_assert_return_minus_errno(mysql, EINVAL);
-    mx_assert_return_minus_errno(mysql->mysql, EBADF);
-
-    error = mysql_errno(mysql->mysql);
-    mx_assert_return_minus_errno((unsigned int)(int)error == error, ERANGE);
-
-    /* no mysql errors possible */
-    return (int)error;
-}
-
 static const char *mx__mysql_error(struct mx_mysql *mysql)
 {
     mx_assert_return_NULL(mysql, EINVAL);
@@ -68,20 +54,6 @@ static const char *mx__mysql_error(struct mx_mysql *mysql)
     return mysql_error(mysql->mysql);
 }
 
-static int mx__mysql_stmt_errno(struct mx_mysql_stmt *stmt)
-{
-    unsigned int error;
-
-    mx_assert_return_minus_errno(stmt, EINVAL);
-    mx_assert_return_minus_errno(stmt->stmt, EBADF);
-
-    error = mysql_stmt_errno(stmt->stmt);
-    mx_assert_return_minus_errno((unsigned int)(int)error == error, ERANGE);
-
-    /* no mysql errors possible */
-    return (int)error;
-}
-
 static int mx__mysql_init(struct mx_mysql *mysql)
 {
     mx_assert_return_minus_errno(mysql, EINVAL);
@@ -121,7 +93,7 @@ static int mx__mysql_real_connect(struct mx_mysql *mysql, const char *host, cons
 
     mx_mysql_save_error(mysql_error(mysql->mysql));
 
-    switch (mx__mysql_errno(mysql)) {
+    switch (mysql_errno(mysql->mysql)) {
         case CR_ALREADY_CONNECTED:
             return -EALREADY;
 
@@ -154,7 +126,7 @@ static int mx__mysql_ping(struct mx_mysql *mysql)
 
     mx_mysql_save_error(mysql_error(mysql->mysql));
 
-    switch (mx__mysql_errno(mysql)) {
+    switch (mysql_errno(mysql->mysql)) {
         case CR_COMMANDS_OUT_OF_SYNC:
             return -EPROTO;
 
@@ -210,7 +182,7 @@ static int mx__mysql_stmt_prepare(struct mx_mysql_stmt *stmt, char *statement)
     }
     mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-    switch (mx__mysql_stmt_errno(stmt)) {
+    switch (mysql_stmt_errno(stmt->stmt)) {
         case CR_OUT_OF_MEMORY:
             return -ENOMEM;
 
@@ -244,7 +216,7 @@ static int mx__mysql_stmt_bind_param(struct mx_mysql_stmt *stmt)
 
     mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-    switch (mx__mysql_stmt_errno(stmt)) {
+    switch (mysql_stmt_errno(stmt->stmt)) {
         case CR_OUT_OF_MEMORY:
             return -ENOMEM;
 
@@ -270,7 +242,7 @@ static int mx__mysql_stmt_bind_result(struct mx_mysql_stmt *stmt)
 
     mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-    switch (mx__mysql_stmt_errno(stmt)) {
+    switch (mysql_stmt_errno(stmt->stmt)) {
         case CR_OUT_OF_MEMORY:
             return -ENOMEM;
 
@@ -296,7 +268,7 @@ static int mx__mysql_stmt_execute(struct mx_mysql_stmt *stmt)
 
     mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-    switch (mx__mysql_stmt_errno(stmt)) {
+    switch (mysql_stmt_errno(stmt->stmt)) {
         case CR_COMMANDS_OUT_OF_SYNC:
             return -EPROTO;
 
@@ -326,7 +298,7 @@ static int mx__mysql_stmt_store_result(struct mx_mysql_stmt *stmt)
 
     mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-    switch (mx__mysql_stmt_errno(stmt)) {
+    switch (mysql_stmt_errno(stmt->stmt)) {
         case CR_COMMANDS_OUT_OF_SYNC:
             return -EPROTO;
 
@@ -372,7 +344,7 @@ static int mx__mysql_stmt_fetch(struct mx_mysql_stmt *stmt)
     if (res == 1) {
         mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-        switch (mx__mysql_stmt_errno(stmt)) {
+        switch (mysql_stmt_errno(stmt->stmt)) {
             case CR_OUT_OF_MEMORY:
                 return -ENOMEM;
 
@@ -412,7 +384,7 @@ static int mx__mysql_stmt_fetch_column(struct mx_mysql_stmt *stmt, unsigned int
         return 0;
     mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-    switch (mx__mysql_stmt_errno(stmt)) {
+    switch (mysql_stmt_errno(stmt->stmt)) {
         case CR_INVALID_PARAMETER_NO:
             return -EPROTO;
 
@@ -493,7 +465,7 @@ static int mx__mysql_stmt_close(struct mx_mysql_stmt *stmt)
     }
     mx_mysql_save_error(mysql_stmt_error(stmt->stmt));
 
-    switch (mx__mysql_stmt_errno(stmt)) {
+    switch (mysql_stmt_errno(stmt->stmt)) {
         case CR_SERVER_GONE_ERROR:
             return -ECONNABORTED;