Re: [HACKERS] \if, \elseif, \else, \endif (was Re: PSQL commands:\quit_if, \quit_unless)

> Revised patch

A comment about control flow and variables:

in branches that are not taken, variables are expanded

nonetheless, in a way that can be surprising.

Case in point:

\set var 'ab''cd'

-- select :var;

\if false

  select :var ;

\else

  select 1;

\endif

The 2nd reference to :var has a quoting hazard, but since it's within

an "\if false" branch, at a glance it seems like this script might work.

In fact it barfs with:

  psql:script.sql:0: found EOF before closing \endif(s)

AFAICS what happens is that :var gets injected and starts a

runaway string, so that as far as the parser is concerned

the \else ..\endif block slips into the untaken branch, as a part of

that unfinished string.