Re: [PATCH] Fix byte char and byte string lexing code

[Thomas Schwinge <thomas@codesourcery.com>]

Hi Mark!

On 2021-09-22T00:54:30+0200, Mark Wielaard <mark@klomp.org> wrote:
> There were two warnings in lexer parse_byte_char and parse_byte_string
> code for arches with signed chars:
>
> rust-lex.cc: In member function
>              ‘Rust::TokenPtr Rust::Lexer::parse_byte_char(Location)’:
> rust-lex.cc:1564:21: warning: comparison is always false due to limited
>                      range of data type [-Wtype-limits]
>  1564 |       if (byte_char > 127)
>       |           ~~~~~~~~~~^~~~~

That's <https://github.com/Rust-GCC/gccrs/pull/343>.

> rust-lex.cc: In member function
>              ‘Rust::TokenPtr Rust::Lexer::parse_byte_string(Location)’:
> rust-lex.cc:1639:27: warning: comparison is always false due to limited
>                      range of data type [-Wtype-limits]
>  1639 |           if (output_char > 127)
>       |               ~~~~~~~~~~~~^~~~~

That's <https://github.com/Rust-GCC/gccrs/pull/344>.

Both these related to <https://github.com/Rust-GCC/gccrs/issues/336>
"GCC '--enable-bootstrap' build".

> The fix would be to cast to an unsigned char before the comparison.
> But that is actually wrong, and would produce the following errors
> parsing a byte char or byte string:
>
> bytecharstring.rs:3:14: error: ‘byte char’ ‘�’ out of range
>     3 |   let _bc = b'\x80';
>       |              ^
> bytecharstring.rs:4:14: error: character ‘�’ in byte string out of range
>     4 |   let _bs = b"foo\x80bar";
>       |              ^
>
> Both byte chars and byte strings may contain up to \xFF (255)
> characters. It is utf-8 chars or strings that can only [truncated here -- but I understand what you mean]

I think this does match my thoughts in
<https://github.com/Rust-GCC/gccrs/pull/343#issuecomment-816214689>.

> Remove the faulty check and add a new testcase bytecharstring.rs
> that checks byte chars and strings do accept > 127 hex char
> escapes, but utf-8 chars and strings reject such hex char escapes.
> ---
>
> https://code.wildebeest.org/git/user/mjw/gccrs/commit/?h=bytecharstring

Thanks, that's now: <https://github.com/Rust-GCC/gccrs/pull/687>
"Fix byte char and byte string lexing code".


Grüße
 Thomas
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