Incorrect error message for byte literal with single quotes

[jcdyer]

When creating a byte literal with single quotes, like b'hello\0', The error message says:

error: character literal may only contain one codepoint
   --> src/wire_protocol/operations.rs:101:37
    |
101 |         assert_eq!(Bson::Binary(4, b'12345').byte_length().unwrap(), 10);
    |                                     ^^^^^^^
help: if you meant to write a `str` literal, use double quotes
    |
101 |         assert_eq!(Bson::Binary(4, b"12345").byte_length().unwrap(), 10);
    |                                     ^^^^^^^

But following the directions would not give us a str literal, it would give a [u8] literal.

[varkor]

This should be easy to fix, by replacing the message with:

if you meant to write a byte string literal, use double quotes

when the literal is prefixed by b.

rust/src/libsyntax/parse/unescape_error_reporting.rs

Line 57 in 60895fd

"if you meant to write a `str` literal, use double quotes",

You may need to see work out which call emit_unescape_error is originating from (in src/libsyntax/parse/lexer/mod.rs) to pass information about the nature of the literal.

[onehr]

Can I work on this? @varkor

[varkor]

@onehr: go ahead! :) Let me know if you have any questions.

[onehr]

@varkor Hi, I have been doing some work in this issue, cause this is the first time I'm sending PR to rust, can you give me some feedback. Thanks!