mine		yours
HTM	1	HTM	1
ASP	31	ASP	1
HTM	31	HTM	31
ASP	44	ASP	31
HTM	46	HTM	46
ASP	50	ASP	46
HTM	50	HTM	50
ASP	55	ASP	50
HTM	59	HTM	59
ASP	73	ASP	59
HTM	75	HTM	75

that is, it counts correctly for HTM blocks, but doesn't increment the line number for ASP blocks. I tried moving the line $line += ... before the push, but it didn't help.

seems to be failing line count.

You're right. Because the regex can match a block of html and a block of asp in one go, in between $line already needs to be updated. So I removed the extra set of parens and the counter line again and added two new \n-counters: one for $1 and one for $2.

my @parsed;
my $line = 1;

while ($asp =~ /\G((?: [^<]+ | <(?!%) )*) (?: <%(.*?)%> | ((?=<%)) )?/
+gsx) {

    $1 and push @parsed, [ $line, html => $1 ];
    $line += $1 =~ tr/\n//;

    $2 and push @parsed, [ $line, asp  => $1 ];
    $line += $2 =~ tr/\n//;

    defined $3 and die "Unclosed ASP code block starting on line $line
+ near '",
        $asp =~ /\G(<%\s*\n?.*)/g, "'.\n";
}
[download]

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }

/\G((?: [^<]+ | <(?!%) )*) (?: <%(.*?)%> | ((?=<%)) )?/gsx

Just for fun, I wanted to try to make a Perl 6 rule from this. Here it is, untested and mostly guessed. I have no idea how to do line numbers, so I cheated and imagined a method of .pos for that :)

rule code_begin ($type) {
    <{
        {
            asp => '<%',
            php => '<?',
            plp => '<:' 
        }.{$type} // fail "Unknown type: $type"
    }>
}

rule code_end ($type) {
    <{
        {
            asp => '%>',
            php => '?>',
            plp => ':>' 
        }.{$type} // fail "Unknown type: $type"
    }>
}

rule code_block ($type) {
    <code_begin $type> (.*?) <code_end $type>
}

rule code_document ($type) {
    [
        # First, match any number of subsequent code blocks.
        [
            { $?line := .pos.line }
            <code_block $type> ::
            { push @?blocks, [ $?line, code => $?code_block ] } 
        ]*
        
        # If there is now a code_begin, obviously that is an open bloc
+k.
        # (In PLP, that is valid, but let's assume for now that it's n
+ot.)
        [ 
            { $?line := .pos.line }
            <code_begin $type> \n* $?context := (\N<,15>) 
            { fail "Unclosed code block on line $?line, near '$?contex
+t'" }
        ]?

        # And then a piece of text.
        # (At least one character, to avoid having empty blocks.)
        [
            { $?line := .pos.line }
            $?html := (.+?) [ <before <code_begin $type>> | $ ] ::
            { push @?blocks, [ $?line, html => $?html ] } 
        ]?
    ]*    
}

my @parsed = ($asp ~~ /<code_document 'asp'>/).{blocks}
[download]

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }