Re: Leading comments and client applications

Rob Sargent <robjsargent(at)gmail(dot)com> writes:
>> As far as the comparison behavior goes, psql's parser strips
>> comments that start with double dashes, for $obscure_reasons.

> That story aught to be worth a $beer or two

Hmm. The original reasoning is lost in the mists of time;
I dug in our git history and traced the behavior as far back
as a45195a19 of 1999-11-04, but I'll bet a nickel that Peter
doesn't remember exactly why he did that.

But I can show you why I gave up on removing the behavior:
it's an important part of psql's strategy of discarding
leading whitespace before a query. Our regression test
scripts are full of cases like

-- comments here

SELECT intentionally-wrong-query;

and what they're expecting to get from that is output like

ERROR: column "intentionally" does not exist
LINE 1: SELECT intentionally-wrong-query;
^

When I changed psql's parser to not remove comments, that output
suddenly changed to say "LINE 3:", because now the query string
sent to the server included the "-- comments here" line as well
as the blank line after it. While we could have changed all the
expected output, or changed how the server counts lines within
a query, we concluded that this would confuse too many people and
break too many applications; so we left it alone.

(As of v15, psql will send -- comments that begin *after* the
first non-whitespace token of a query [1]. But leading comments
and whitespace will still get stripped.)

regards, tom lane

[1] https://git.postgresql.org/gitweb/?p=postgresql.git&a=commitdiff&h=83884682f4df96184549b91869a1cf79dafb4f94