[Bug d/105544] gdc fails to compile d source from stdin

["fabian@ritter-vogt.de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105544

--- Comment #9 from Fabian Vogt <fabian@ritter-vogt.de> ---
(In reply to ibuclaw from comment #8)
> (In reply to Fabian Vogt from comment #6)
> > I had a quick debugging session: The DMD lexer code doesn't really care
> > about the size of the buffer and instead runs until it encounters either a 0
> > or 0x1A byte. The stdin read loop in d_parse_file doesn't explicitly
> > 0-terminate the buffer, which means that it works randomly...
> > 
> 
> OK, so the suggestion would be to zero the padding at the end of the input
> buffer then.
>
> --- a/gcc/d/d-lang.cc
> +++ b/gcc/d/d-lang.cc
> @@ -1072,6 +1072,10 @@ d_parse_file (void)
>  				      global.params.doHdrGeneration);
>  	  modules.push (m);
>  
> +	  /* Zero the padding past the end of the buffer so the D lexer has a
> +	     sentinel.  The lexer only reads up to 4 bytes at a time.  */
> +	  memset (buffer + len, '\0', 16);
> +
>  	  /* Overwrite the source file for the module, the one created by
>  	     Module::create would have a forced a `.d' suffix.  */
>  	  m->src.length = len;

Yep, that should work. Though I wonder why 16B of padding and not just a single
byte for the 0. FWICT the lexer reads a single byte at a time only (utf8_t is
an unsigned char), so it should stop at the first 0.

The comment above explaining the padding mentions a "final '\n'" which should
probably be adjusted with the change to \0.