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From: Rene Rivera (grafik.list_at_[hidden])
Date: 2005-10-31 02:26:37

Reece Dunn wrote:
> The results of the discussion on the "[BBv2] fix for response file
> regeneration" thread was to have builtin support for response files
> using the @(...) syntax based on Matt Armstrong's perforce Jam branch.
> The bjam-response.diff patch adds @(...) syntax support for NT builds of
> BJam. This is based on Matt's code but was written from scratch and is
> improved from my initial submission. When you use @(...) the code (in
> variable.c) expands the variables in the '...' to a temporary file and
> then outputs the location of that file.

How does Matt's version of the syntax @() work? I'm asking because I was
going to apply, with some mods, your patch but I decided not to because
I have some concerns. Instead I just refactored the tmpdir function in
preparation, with my own simpler implementation (both Windows and Unix).

My basic concern is that as you implemented @() is the limited response
file specific functionality. I really loath adding generic looking
syntax that isn't generic. The limitation is that there is no control
over what the name of the temporary files are. In particular they are
fixed to have an ".RSP" extension. Since I'm not one to usually be
critical without having some suggestions one how to fix things here's
what I'm thinking...

The "@()" is ultimately a "here document" functionality. With that in
mind I'd rather have it be as flexible as possible. My suggestion is to
use the standard variable expansion syntax to manage control of where
and how the document is put together. Like so:

1) For a temporary file:

@($(TMPFILE):S=.txt:E="This is some content.")

And like your changes the @() would evaluate to the name of the
temporary file.

2) For doing std output:

@($(STDOUT):E="Some console output")

This would allow writing actions that take standard input without having
to resort to echo. For example:

actions xyz
@($(STDOUT):E="$(>)") | sort > $(<)

3) Similarly for STDERR.

Note: the $(TMPFILE) and $(STDOUT) could just as well be TMPFILE and
STDOUT (without the $()). But the $() seems more fitting to me.

The above has enough flexibility to be useful in many context. In
particular, in addition to the response file use, it would allow for a
less kludgy implementation of the "print" module. It would no longer
need to do the funky string escape manipulations to get over the shell
echo command use. And because of that reduce the memory consumption
(print.text is one of the top 3 memory consuming rules in BBv2). And
apply that to any other place where BBv2 needs to escape strings so they
can be handed to the shell echo or some other command that can handle
std input.

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