Why does contain_leaked_vars believe MinMaxExpr is safe?

On Tue, May 12, 2015 at 7:22 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

MinMaxExpr is an implicit invocation of a btree comparison function.
Are we supposing that all of those are necessarily leakproof?

I suspect it's an oversight, because the comment gives no hint that
any such intention was present. It's been more than three years since
I committed that code (under a different function name) so my memory
is a little fuzzy, but I believe it just didn't occur to me that
MinMaxExpr could include a function call.

I suspect it's safe in practice, but in theory it's probably a bug.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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On Wed, May 13, 2015 at 09:34:53AM -0400, Robert Haas wrote:

On Tue, May 12, 2015 at 7:22 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

MinMaxExpr is an implicit invocation of a btree comparison function.
Are we supposing that all of those are necessarily leakproof?

I suspect it's an oversight, because the comment gives no hint that
any such intention was present. It's been more than three years since
I committed that code (under a different function name) so my memory
is a little fuzzy, but I believe it just didn't occur to me that
MinMaxExpr could include a function call.

I suspect it's safe in practice, but in theory it's probably a bug.

Agreed; it is formally a bug. We considered[1]/messages/by-id/20110707223526.GJ1840@tornado.leadboat.com special trust of operator
class members and decided against it. Since almost every btree opfamily
member is leakproof in practice, I doubt the bug has harmed anyone.

[1]: /messages/by-id/20110707223526.GJ1840@tornado.leadboat.com

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