MySQL Bugs: #58344: Support nested (C-style) comments

Bug #58344	Support nested (C-style) comments
Submitted:	20 Nov 2010 5:41	Modified:	20 Nov 2010 8:37
Reporter:	Terry Nycum	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Parser	Severity:	S4 (Feature request)
Version:	5.1	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	comment, syntax

Description:
Per http://dev.mysql.com/doc/refman/5.1/en/comments.html:
"Nested comments are not supported. (Under some conditions, nested comments might be permitted, but usually are not, and users should avoid them.)"

To quote from a comment on http://bugs.mysql.com/bug.php?id=57509:
"The cases where it works is just a side effect of the flexibility in the implementation. It is not designed with the purpose to parse nested comments."

This request is fairly simple: design it with that purpose.

If comment parsing is already implemented flexibly in one place, why is it reimplemented--at all, much less inflexibly--elsewhere?

http://bugs.mysql.com/bug.php?id=30631, http://bugs.mysql.com/bug.php?id=39559, http://bugs.mysql.com/bug.php?id=44189, http://bugs.mysql.com/bug.php?id=57509 ... --all dodge the obvious solution. You'd think the parser were some kludge that no one wanted to touch.

How to repeat:
n/a (not a bug)

Suggested fix:
See fix suggested for http://bugs.mysql.com/bug.php?id=4313

Why should we support it? Besides people assuming things that clearly aren't supported. Keep in mind that every change like this increases the complexity of the parser and slowdowns it a bit.

I also think there is a misunderstanding around what is the purpose of "undefined behavior" cases.

http://en.wikipedia.org/wiki/Undefined_behavior

> If comment parsing is already implemented flexibly in one place, why is
> it reimplemented--at all, much less inflexibly--elsewhere?

Keep in mind that we aren't responsible for design decisions elsewhere. If other places decide to support nested comments, that's their burden to carry, not ours. Here we also have to think about the long term maintainability and performance of the parser, which can affect everyone.