$ cat .gitattributes *.py filter=pyspace $ cat .gitconfig [filter "pyspace"] smudge = cat clean = pyspace.pl --file %f required

pyspace.pl

#!/usr/bin/perl

use strict;
use warnings;
use 5.10.0;
use Getopt::Long;
use Data::Dumper;

my $filename;
my $line_count = 0;
my @lines = ();
my @tmp = ();
my $reported_filename;
GetOptions("file=s", => \$reported_filename) or die("Error in command line args $!");

$filename = shift @ARGV;

if ($filename) {
	print "opening $filename";
	open my $fp, $filename or die "Failed to open '$filename': $!";
	while (<$fp>) { chomp; push @lines, $_; }
	close $fp;
	$reported_filename = $filename if not $reported_filename;
}
else {
	$filename = '<STDIN>';
	while (<>) { chomp; push @lines, $_; }
}

=pod

Preprocessing: if a line ends in a backslash, then the following line does not
follow the same tabbing patterns

=cut
my $in_string = 0;
my $qq = '';
my $last_was_continuuing = 0;
sub check_str {
	my $q = shift @_;
	if ($qq ne '' && $q eq $qq && !$in_string) {
		$in_string = 0;
	}
	elsif ($q ne '' && !$in_string) {
		$qq = $q;
		$in_string = 1;
	}
}
for my $line (@lines) {
	my $i = 0;
	my ($c1, $c2, $c3);
	
	if ($in_string) {
		$line = "\2$line";
	}
	elsif ($last_was_continuuing) {
		$line = "\1$line";
	}
	
	while ($i < length $line) {
		$c1 = substr $line, $i, 1;
		if ($c1 eq '"' or $c1 eq "'") {
			$c2 = substr $line, $i+1, 1;
			if ($c2 eq $c1) {
				$c3 = substr $line, $i+2, 1;
				if ($c3 eq $c1) {
					# triple quotes
					check_str($c1 x 3);
					$i += 2
				}
				else {
					# double quotes
					check_str($c1 x 2);
					$i += 1
				}
			}
			else {
				# single quotes
				check_str($c1);
			}
		}
		$i++;
	}
	
	$last_was_continuuing = $line =~ /^.*?\\\s*(?:#.*)?$/;
	#print("continue=$last_was_continuuing, in_string=$in_string, line=\"$line\"\n");
	unshift @tmp, $line;
}


@lines = @tmp;
@tmp = ();
$line_count = scalar @lines;

=pod

Our tabbing rules follow a simple rule:
 If a line is completely whitespace, then it should be indented the same as
 the following non-whitespace-only line.
 
Algorithm:
 for each line in file from end to beginning:
   if line is not whitespace:
     set ntabs = get_indent(line)
   else:
     line = '\t' * ntabs + nontabs

=cut

my $ntabs = 0;
my $last_was_empty = 0;
my $l = 0;
for my $line (@lines) {
	$l++;
	if (substr($line, 0, 1) eq "\2") {
		# a string
		unshift @tmp, substr $line, 1;
		$last_was_empty = 0;
	}
    elsif ($line =~ m/^\x01?\s*$/) {
        if (!$last_was_empty) {
            unshift @tmp, ("\t" x $ntabs);
        }
        $last_was_empty = 1;
    }
    elsif ($line =~ m/^(\x01)?([ ]*)((?:.*)|(?:#.*))$/) {
        my ($continuation, $indent, $content) = ($1, $2, $3);
        
        if ($continuation) {
        	my $alignment = '';
        	# Just assume that the tabber is correct in these cases
        
=pod
        	
        	
        	if ($indent =~ m/^\t*$/) {
        		# All tabs
        		if (length($indent) > $ntabs) {
        			$alignment = "\t" x (length($indent) - $ntabs);
        		}
        	}
        	elsif ($indent =~ m/^\t+(\s*)$/) {
        		# tab indent, space alignment
        		$alignment = $1;
        	}
        	elsif ($indent =~ m/^\s*$/) {
        		# All spaces, assume 4 spaces/tab
        		$alignment = " " x (length($indent) - ($ntabs * 4));
        	}

=cut

        	
        	unshift @tmp, $indent . $content;
        }
        else {
		    $ntabs = estimateTabs($indent, $line_count - $l + 1, $content);
		    
		    
		    unshift @tmp, ("\t" x $ntabs) . $content;
		}
        $last_was_empty = 0;
    }
    else {
        die "Unknown line '$line'";
    }
}

if ($filename and $filename ne '<STDIN>') {
	open my $fh, '>', "$filename.tmp" or die $!;
	print $fh join "\n", @tmp, '';
	close $fh;
}
else {
	print join "\n", @tmp, '';
}

sub estimateTabs {
    my $indent = shift;
    my $lineno = shift;
    my $content = shift;
    if ($indent =~ m/[^\t]/) {
        my $spaces = length($indent);
        if ($spaces % 4 == 0) {
            return $spaces / 4;
        }
        elsif ($spaces % 8 == 0) {
            return $spaces / 8;
        }
        elsif ($spaces % 6 == 0) {
            return $spaces / 6;
        }
        elsif ($spaces % 2 == 0) {
            return $spaces / 2;
        }
        elsif ($spaces == 0) {
            return 0;
        }
        else {
            die "Unknown indent size '$indent' in $reported_filename:$lineno, content=\"$content\"";
        }
    }

    return length($indent);
}