Re: Patch for psql History Display on MacOSX

Stepan Rutz <stepan(dot)rutz(at)gmx(dot)de> writes:
> Attached is a very trivial patch as a basis for discussion that at least makes \s (show history) work in psql on Macs. Macs uses libedit, which has a libreadline interface.

Hm. The $64 question here is whether we can assume that history_get()
exists and works compatibly in every interesting version of libreadline
and libedit.

I poked into the oldest version of GNU readline I could find, 4.0
(released in 1999), and that has it. The oldest libedit I have around
is the one that came with OSX 10.4 (the CVS marker in readline.h from
that says 2004/01/17). That has it too. So that looks pretty good.

The readline code says that the argument ranges from "history_base"
up, not from 1 up as this patch assumes. And it looks like history_base
can change once the max number of stored lines is exceeded, so we can't
assume that 1 is good enough. Fortunately, the global variable
history_base also exists in both libraries (though it looks like it
never changes from 1 in libedit).

Functionally this seems like a clear win over what we had, especially
since it supports using the pager. I'm inclined to think we should
not only apply this change but back-patch it.

One thing worth thinking about: should we use a history_get() loop
like this for *all* \s commands, even when the target file is a
regular file not /dev/tty? libedit's version of write_history does
not write the history "in the clear" exactly, which you would think
is the behavior wanted when saving a command history for any purpose
other than updating ~/.psql_history. Such a change would break a
workflow that involves doing \s to some random file and then copying
that file to ~/.psql_history, but I find it hard to fathom why anyone
would do that.

There are a couple other minor bugs and some cosmetic things I don't like
in this patch, but I'm willing to fix it up and commit it if there
are not objections.

regards, tom lane