Bug#458789: uscan: framework for using external scripts: qx/script/

[Osamu Aoki]

Hi,

Let me propose a new generic mangle rule: qx/script/

This mangles by feeding the target $string into the STDIN of script in
the debian directory and reading its STDOUT back into the target
$string.

This works somewhat like a Perl command thus I used qx as the initiating
command.

    $script = qx"debian/script";

This is applicable to all mangle rules :-)  including pagemangle I
proposed in https://bugs.debian.org/797787 Message #15. (Disregard the
old patch in Message #5 and #10)  The exact patch will be posted there
later.

At least this and pagemangle facilitate users to setup a watch file for
the following bug reports:

 #451051 Please support parsing .lsm files
 #458789 Please allow framework for using external scripts
 #614802 watch file syntax for taking version from timestamp
         ==> The last one needs a new mangling rule after the download.

This is a very generic tool to address many random feature requests
which devscripts maintainer can not be keeping up with.

I just made a proof of concept code snippet which changes the start of
uscan safe_replace($$) as follows:
---------
sub safe_replace($$) {
    my ($in, $pat) = @_;
    $pat =~ s/^\s*(.*?)\s*$/$1/;

    $pat =~ /^(s|tr|y|qx)(.)/;
    my ($op, $sep) = ($1, $2 || '');
    my $esc = "\Q$sep\E";
    my ($parsed_ok, $regexp, $replacement, $flags);

    if ($op eq 'qx') {
        my $input = $$in;
        my $output;
        # script name: [a-zA-Z0-9][-_a-zA-Z0-9]* (any quotation dropped)
        $pat  =~ s/^qx[^-_a-zA-Z0-9]*([a-zA-Z0-9][-_a-zA-Z0-9]*)[^-_a-zA-Z0-9]*$/debian\/$1/;
        if ( -x $pat) {
            spawn(exec => $pat,
            from_string => \$input,
            to_string => \$output,
            wait_child => 1);
            $$in = $output;
            return 1;
        } else {
            print STDERR "$progname warning: missing executable $pat: $!\n";
            return 0;
        }
    } elsif ($sep eq '{' or $sep eq '(' or $sep eq '[' or $sep eq '<') {
...
---------

So we can use this as:
  opts="pagemangle=qx/script/;suffix=+dfsg1;dversionmangle=s/+dfsg\d*$//" ...

There are relatively strict limitations to the script name for the safe
operation.

This uses Dpkg::IPC and I tested the above code in a mock code
environment and works nicely.

Regards,

Osamu