I want to have the tool scan the source code for “uses” and “require” statements, and generate a nice package that will automatically retrieve from CPAN and install the packages that this app needs. “DWIM,” y’know...

I would recommend against that, though it would be nice. It is not self-documenting. Too much voodoo.

Module::Install is really very nice and self-bundling. I.e., MI does not have to be installed on the target machine. It's good at pulling in CPAN deps and such when you run its Makefile.PL. And that is where the real task is. The Perl makefile is just a script. They come with lots of features from the various installers but they're still just scripts. I did one recently that fetched zipped dists of thirdparty JS stuff and installed it automatically when the makefile was run. That way no external libs are in the source control; only in the dist. Again, kudos to adamk is due. He maintains the archive zip stuff too, I think.

The other good thing about makefiles is they document their requirements both for man and machine. If you do end up writing a scanning script, have it write your makefile requires statements for you. Best of both. Share it if you do!

Oh, congratulations, too! Feels great to get a project done well.

If you're trying to find out what modules your program is using, then the following piece of magic may suffice:

END {
  foreach my $file (sort keys %INC) {
    my $module  = $file ;
    my $located = $INC{$file} ;
    $module =~ s|\.pm$|| ;
    $module =~ s|[/\\]|::|g ;
    my $version ;
    { no strict 'refs' ; $version = ${$module.'::VERSION'} || '??' ; }
+ ;
    print STDERR "$module v$version $located\n" ;
  } ;
} ;
[download]

Mind you, this will miss any require operations which your test run does not actually execute... I cannot imagine that this will be a problem, but it's tricky to guarantee. If that worries you, you can try:

END {
  my %myINC = () ;
  foreach my $file (keys %INC) {
    my $module = $file ;
    $module =~ s|\.pm$|| ;
    $module =~ s|[/\\]|::|g ;
    $myINC{$module} = $INC{$file} ;
  } ;

  foreach my $module (sort keys %myINC) {
    my $located = $myINC{$module} ;
    my $version ;
    { no strict 'refs' ; $version = ${$module.'::VERSION'} || '??' ; }
+ ;
    print STDERR "$module v$version $located\n" ;

    open my $FH, "<", $located   or die "failed to open $located: $!" 
+;
    while (<$FH>) {
      if ((m/^(?:\s+|[^#;];\s*)*?require\s+([A-Za-z]\w+(?:::\w+)*)\b/)
                                                  && !exists($myINC{$1
+})) {
        printf STDERR " %5d: %s", $., $_ ;
      } ;
    } ;
  } ;
} ;
[download]

NB: this comes without warranty of any kind, in particular no warranty of fitness for any purpose whatsoever; and if you use this you acknowledge that such exclusion of warranty is entirely reasonable, given the level of the fee :-)

my @pkgs = map { s,[/\\],::,g; s,\.pm$,,} keys %INC;
[download]