Change:
fn consume_block_comment(rdr: @mut StringReader) -> Option<TokenAndSpan> { // block comments starting with "/**" or "/*!" are doc-comments <del> let res = if rdr.curr == '*' || rdr.curr == '!' { let start_bpos = rdr.pos - BytePos(3u); while !(rdr.curr == '*' && nextch(rdr) == '/') && !is_eof(rdr) { bump(rdr); } </del> <ins> let is_doc_comment = rdr.curr == '*' || rdr.curr == '!'; let start_bpos = rdr.pos - BytePos(if is_doc_comment {3u} else {2u}); let mut level: int = 1; while level > 0 { </ins> if is_eof(rdr) { <del> fatal_span(rdr, start_bpos, rdr.last_pos, ~"unterminated block doc-comment"); } else { </del> <ins> let msg = if is_doc_comment { ~"unterminated block doc-comment" } else { ~"unterminated block comment" }; fatal_span(rdr, start_bpos, rdr.last_pos, msg); } else if rdr.curr == '/' && nextch(rdr) == '*' { level += 1; </ins> bump(rdr); bump(rdr); <del> do with_str_from(rdr, start_bpos) |string| { // but comments with only "*"s between two "/"s are not if !is_block_non_doc_comment(string) { Some(TokenAndSpan{ tok: token::DOC_COMMENT(str_to_ident(string)), sp: codemap::mk_sp(start_bpos, rdr.pos) }) } else { None } } </del> <ins> } else if rdr.curr == '*' && nextch(rdr) == '/' { level -= 1; bump(rdr); bump(rdr); } else { bump(rdr); </ins> } <del> } else { let start_bpos = rdr.last_pos - BytePos(2u); loop { if is_eof(rdr) { fatal_span(rdr, start_bpos, rdr.last_pos, ~"unterminated block comment"); } if rdr.curr == '*' && nextch(rdr) == '/' { bump(rdr); bump(rdr); break; </del> <ins> } let res = if is_doc_comment { do with_str_from(rdr, start_bpos) |string| { // but comments with only "*"s between two "/"s are not if !is_block_non_doc_comment(string) { Some(TokenAndSpan{ tok: token::DOC_COMMENT(str_to_ident(string)), sp: codemap::mk_sp(start_bpos, rdr.pos) }) </ins> } else { <del> bump(rdr); </del> <ins> None </ins> } } <ins> } else { </ins> None }; <del> // restart whitespace munch. if res.is_some() { res } else { consume_whitespace_and_comments(rdr) } </del> <ins> // restart whitespace munch. if res.is_some() { res } else { consume_whitespace_and_comments(rdr) } </ins> } fn scan_exponent(rdr: @mut StringReader, start_bpos: BytePos) -> Option<~str> {

Discussion:
Currently we don't support nested block comments. This allows lexing to be regular, but it widely seen as an inconvenience. Modify the lexer to keep track of comment nesting. Nominating backcompat.
I thought we were going to grow a macro to handle block quotes. Did that ever get implemented?
I don't know what you mean by block quotes.
Accepted for feature-complete
Don't line comments address pretty much all uses of nested block comments?
by block quote, I mean in the style of CPP's to allow for nesting comments. Something like this:
From what I've gathered from the code, there are two implementations of the comment parsing, one of which supports nested comments, so I guess should be fixed before this bug.
That's pretty funny that the pretty printer already supports nested comments. I don't think they necessarily have to be merged to fix this bug, though our lexing is a bit of a mess.
Are you going to tackle this?
If there's no massive refactoring to do, I can try! Expect a PR soon.
The reference manual says "Comments in Rust code follow the general C++ style of line and block-comment forms, with no nesting of block-comment delimiters" ... right after production rules for nested comments.
looks like it was forgotten to be updated, thanks for noticing! (I opened )