Bug: Mis-formatted error diagnostics for incorrect function use

[creachadair]

Repro:

$ srcd sql
mysql> select split("a,b", ",", 1);

Observed:

ERROR 1105 (HY000): unknown error: %!s(int=2): expecting 3 arguments for calling this function, %!d(MISSING) received

Expected:

• Since it turns out that split only accepts two arguments, I would expect the diagnostic to report that 2 arguments are expected, not 3 (I assume the latter is because the implementation has a receiver or something hidden from the query API).

• The error should not be classified as "unknown": It's either a syntax error or invalid parameters, but it is fully under the control of the CLI.

• I expect the format strings to match their type, so that it says something like

  ERROR: split: expected 2 arguments, received 3.

  instead of having the auto-generated fallbacks from the fmt package like %!d(MISSING).

• I expect the error string to mention the name of the function I got wrong. In this case it is obvious, but in a bigger query it would not be.

[kuba--]

ERROR 1105 (HY000): unknown error: comes from vitess.
We can fix invalid argument argument description as suggested .

[creachadair]

🤘#666

Thank you!