renderComments

fn renderComments(r: *Render, start: usize, end: usize) Error!bool {
    const tree = r.tree;
    const ais = r.ais;

    var index: usize = start;
    while (mem.find(u8, tree.source[index..end], "//")) |offset| {
        const comment_start = index + offset;

        // If there is no newline, the comment ends with EOF
        const newline_index = mem.findScalar(u8, tree.source[comment_start..end], '\n');
        const newline = if (newline_index) |i| comment_start + i else null;

        const untrimmed_comment = tree.source[comment_start .. newline orelse tree.source.len];
        const trimmed_comment = mem.trimEnd(u8, untrimmed_comment, &std.ascii.whitespace);

        // Don't leave any whitespace at the start of the file
        if (index != 0) {
            if (index == start and mem.containsAtLeast(u8, tree.source[index..comment_start], 2, "\n")) {
                // Leave up to one empty line before the first comment
                try ais.insertNewline();
                try ais.insertNewline();
            } else if (mem.findScalar(u8, tree.source[index..comment_start], '\n') != null) {
                // Respect the newline directly before the comment.
                // Note: This allows an empty line between comments
                try ais.insertNewline();
            } else if (index == start) {
                // Otherwise if the first comment is on the same line as
                // the token before it, prefix it with a single space.
                try ais.writeByte(' ');
            }
        }

        index = 1 + (newline orelse end - 1);

        const comment_content = mem.trimStart(u8, trimmed_comment["//".len..], &std.ascii.whitespace);
        if (ais.disabled_offset != null and mem.eql(u8, comment_content, "zig fmt: on")) {
            // Write the source for which formatting was disabled directly
            // to the underlying writer, fixing up invalid whitespace.
            const disabled_source = tree.source[ais.disabled_offset.?..comment_start];
            try writeFixingWhitespace(ais.underlying_writer, disabled_source);
            // Write with the canonical single space.
            try ais.underlying_writer.writeAll("// zig fmt: on\n");
            ais.disabled_offset = null;
            ais.resetLine();
        } else if (ais.disabled_offset == null and mem.eql(u8, comment_content, "zig fmt: off")) {
            // Write with the canonical single space.
            try ais.writeAll("// zig fmt: off\n");
            ais.disabled_offset = index;
        } else {
            // Write the comment minus trailing whitespace.
            try ais.print("{s}\n", .{trimmed_comment});
        }
    }

    if (index != start and mem.containsAtLeast(u8, tree.source[index - 1 .. end], 2, "\n")) {
        // Don't leave any whitespace at the end of the file
        if (end != tree.source.len) {
            try ais.insertNewline();
        }
    }

    return index != start;
}