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package B::Lint;
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=head1 NAME
B::Lint - Perl lint
=head1 SYNOPSIS
perl -MO=Lint[,OPTIONS] foo.pl
=head1 DESCRIPTION
The B::Lint module is equivalent to an extended version of the B<-w>
option of B<perl>. It is named after the program B<lint> which carries
out a similar process for C programs.
=head1 OPTIONS AND LINT CHECKS
Option words are separated by commas (not whitespace) and follow the
usual conventions of compiler backend options. Following any options
(indicated by a leading B<->) come lint check arguments. Each such
argument (apart from the special B<all> and B<none> options) is a
word representing one possible lint check (turning on that check) or
is B<no-foo> (turning off that check). Before processing the check
arguments, a standard list of checks is turned on. Later options
override earlier ones. Available options are:
=over 8
=item B<context>
Produces a warning whenever an array is used in an implicit scalar
context. For example, both of the lines
    $foo = length(@bar);
    $foo = @bar;
will elicit a warning. Using an explicit B<scalar()> silences the
warning. For example,
    $foo = scalar(@bar);
=item B<implicit-read> and B<implicit-write>
These options produce a warning whenever an operation implicitly
reads or (respectively) writes to one of Perl's special variables.
For example, B<implicit-read> will warn about these:
    /foo/;
and B<implicit-write> will warn about these:
    s/foo/bar/;
Both B<implicit-read> and B<implicit-write> warn about this:
    for (@a) { ... }
=item B<dollar-underscore>
This option warns whenever $_ is used either explicitly anywhere or
as the implicit argument of a B<print> statement.
=item B<private-names>
This option warns on each use of any variable, subroutine or
method name that lives in a non-current package but begins with
an underscore ("_"). Warnings aren't issued for the special case
of the single character name "_" by itself (e.g. $_ and @_).
=item B<undefined-subs>
This option warns whenever an undefined subroutine is invoked.
This option will only catch explicitly invoked subroutines such
as C<foo()> and not indirect invocations such as C<&$subref()>
or C<$obj-E<gt>meth()>. Note that some programs or modules delay
definition of subs until runtime by means of the AUTOLOAD
mechanism.
=item B<regexp-variables>
This option warns whenever one of the regexp variables $', $& or
$' is used. Any occurrence of any of these variables in your
program can slow your whole program down. See L<perlre> for
details.
=item B<all>
Turn all warnings on.
=item B<none>
Turn all warnings off.
=back
=head1 NON LINT-CHECK OPTIONS
=over 8
=item B<-u Package>
Normally, Lint only checks the main code of the program together
with all subs defined in package main. The B<-u> option lets you
include other package names whose subs are then checked by Lint.
=back
=head1 BUGS
This is only a very preliminary version.
=head1 AUTHOR
Malcolm Beattie, mbeattie@sable.ox.ac.uk.
=cut
use strict;
use B qw(walkoptree_slow main_root walksymtable svref_2object parents
         OPf_WANT_LIST OPf_WANT OPf_STACKED G_ARRAY
        );
my $file = "unknown";           # shadows current filename
my $line = 0;                   # shadows current line number
my $curstash = "main";          # shadows current stash
# Lint checks
my %check;
my %implies_ok_context;
BEGIN {
    map($implies_ok_context{$_}++,
        qw(scalar av2arylen aelem aslice helem hslice
           keys values hslice defined undef delete));
}
# Lint checks turned on by default
my @default_checks = qw(context);
my %valid_check;
# All valid checks
BEGIN {
    map($valid_check{$_}++,
        qw(context implicit_read implicit_write dollar_underscore
           private_names undefined_subs regexp_variables));
}
# Debugging options
my ($debug_op);
my %done_cv;            # used to mark which subs have already been linted
my @extra_packages;     # Lint checks mainline code and all subs which are
                        # in main:: or in one of these packages.
sub warning {
    my $format = (@_ < 2) ? "%s" : shift;
    warn sprintf("$format at %s line %d\n", @_, $file, $line);
}
# This gimme can't cope with context that's only determined
# at runtime via dowantarray().
sub gimme {
    my $op = shift;
    my $flags = $op->flags;
    if ($flags & OPf_WANT) {
        return(($flags & OPf_WANT_LIST) ? 1 : 0);
    }
    return undef;
}
sub B::OP::lint {}
sub B::COP::lint {
    my $op = shift;
    if ($op->name eq "nextstate") {
        $file = $op->file;
        $line = $op->line;
        $curstash = $op->stash->NAME;
    }
}
sub B::UNOP::lint {
    my $op = shift;
    my $opname = $op->name;
    if ($check{context} && ($opname eq "rv2av" || $opname eq "rv2hv")) {
        my $parent = parents->[0];
        my $pname = $parent->name;
        return if gimme($op) || $implies_ok_context{$pname};
        # Two special cases to deal with: "foreach (@foo)" and "delete $a{$b}"
        # null out the parent so we have to check for a parent of pp_null and
        # a grandparent of pp_enteriter or pp_delete
        if ($pname eq "null") {
            my $gpname = parents->[1]->name;
            return if $gpname eq "enteriter" || $gpname eq "delete";
        }
        warning("Implicit scalar context for %s in %s",
                $opname eq "rv2av" ? "array" : "hash", $parent->desc);
    }
    if ($check{private_names} && $opname eq "method") {
        my $methop = $op->first;
        if ($methop->name eq "const") {
            my $method = $methop->sv->PV;
            if ($method =~ /^_/ && !defined(&{"$curstash\::$method"})) {
                warning("Illegal reference to private method name $method");
            }
        }
    }
}
sub B::PMOP::lint {
    my $op = shift;
    if ($check{implicit_read}) {
        if ($op->name eq "match" && !($op->flags & OPf_STACKED)) {
            warning('Implicit match on $_');
        }
    }
    if ($check{implicit_write}) {
        if ($op->name eq "subst" && !($op->flags & OPf_STACKED)) {
            warning('Implicit substitution on $_');
        }
    }
}
sub B::LOOP::lint {
    my $op = shift;
    if ($check{implicit_read} || $check{implicit_write}) {
        if ($op->name eq "enteriter") {
            my $last = $op->last;
            if ($last->name eq "gv" && $last->gv->NAME eq "_") {
                warning('Implicit use of $_ in foreach');
            }
        }
    }
}
sub B::SVOP::lint {
    my $op = shift;
    if ($check{dollar_underscore} && $op->name eq "gvsv"
        && $op->gv->NAME eq "_")
    {
        warning('Use of $_');
    }
    if ($check{private_names}) {
        my $opname = $op->name;
        if ($opname eq "gv" || $opname eq "gvsv") {
            my $gv = $op->gv;
            if ($gv->NAME =~ /^_./ && $gv->STASH->NAME ne $curstash) {
                warning('Illegal reference to private name %s', $gv->NAME);
            }
        }
    }
    if ($check{undefined_subs}) {
        if ($op->name eq "gv"
            && $op->next->name eq "entersub")
        {
            my $gv = $op->gv;
            my $subname = $gv->STASH->NAME . "::" . $gv->NAME;
            no strict 'refs';
            if (!defined(&$subname)) {
                $subname =~ s/^main:://;
                warning('Undefined subroutine %s called', $subname);
            }
        }
    }
    if ($check{regexp_variables} && $op->name eq "gvsv") {
        my $name = $op->gv->NAME;
        if ($name =~ /^[&'`]$/) {
            warning('Use of regexp variable $%s', $name);
        }
    }
}
sub B::GV::lintcv {
    my $gv = shift;
    my $cv = $gv->CV;
    #warn sprintf("lintcv: %s::%s (done=%d)\n",
    #            $gv->STASH->NAME, $gv->NAME, $done_cv{$$cv});#debug
    return if !$$cv || $done_cv{$$cv}++;
    my $root = $cv->ROOT;
    #warn "    root = $root (0x$$root)\n";#debug
    walkoptree_slow($root, "lint") if $$root;
}
sub do_lint {
    my %search_pack;
    walkoptree_slow(main_root, "lint") if ${main_root()};
     
    # Now do subs in main
    no strict qw(vars refs);
    my $sym;
    local(*glob);
    while (($sym, *glob) = each %{"main::"}) {
        #warn "Trying $sym\n";#debug
        svref_2object(\*glob)->EGV->lintcv unless $sym =~ /::$/;
    }
    # Now do subs in non-main packages given by -u options
    map { $search_pack{$_} = 1 } @extra_packages;
    walksymtable(\%{"main::"}, "lintcv", sub {
        my $package = shift;
        $package =~ s/::$//;
        #warn "Considering $package\n";#debug
        return exists $search_pack{$package};
    });
}
sub compile {
    my @options = @_;
    my ($option, $opt, $arg);
    # Turn on default lint checks
    for $opt (@default_checks) {
        $check{$opt} = 1;
    }
  OPTION:
    while ($option = shift @options) {
        if ($option =~ /^-(.)(.*)/) {
            $opt = $1;
            $arg = $2;
        } else {
            unshift @options, $option;
            last OPTION;
        }
        if ($opt eq "-" && $arg eq "-") {
            shift @options;
            last OPTION;
        } elsif ($opt eq "D") {
            $arg ||= shift @options;
            foreach $arg (split(//, $arg)) {
                if ($arg eq "o") {
                    B->debug(1);
                } elsif ($arg eq "O") {
                    $debug_op = 1;
                }
            }
        } elsif ($opt eq "u") {
            $arg ||= shift @options;
            push(@extra_packages, $arg);
        }
    }
    foreach $opt (@default_checks, @options) {
        $opt =~ tr/-/_/;
        if ($opt eq "all") {
            %check = %valid_check;
        }
        elsif ($opt eq "none") {
            %check = ();
        }
        else {
            if ($opt =~ s/^no-//) {
                $check{$opt} = 0;
            }
            else {
                $check{$opt} = 1;
            }
            warn "No such check: $opt\n" unless defined $valid_check{$opt};
        }
    }
    # Remaining arguments are things to check
     
    return \&do_lint;
}
1;