Subject: Re: [PATCH 08/26] diff.c: migrate emit_line_checked to use emit_diff_symbol

From: Junio C Hamano <[email-masked]>
Date: Wed, 21 Jun 2017 13:05:07 -0700

Stefan Beller <[email-masked]> writes:

>  static void emit_add_line(const char *reset,
>  			  struct emit_callback *ecbdata,
>  			  const char *line, int len)
>  {
> -	emit_line_checked(reset, ecbdata, line, len,
> -			  DIFF_FILE_NEW, WSEH_NEW, '+');
> +	unsigned flags = WSEH_NEW | ecbdata->ws_rule;
> +	if (new_blank_line_at_eof(ecbdata, line, len))
> +		flags |= DIFF_SYMBOL_CONTENT_BLANK_LINE_EOF;
> +
> +	emit_diff_symbol(ecbdata->opt, DIFF_SYMBOL_PLUS, line, len, flags);
>  }

This is a bit unsatisfactory that the original code didn't even have
to make a call to new_blank_line_at_eof() at all when we know we are
not checking for / coloring whitespace errors, but the function is
called unconditionally in the new code.

> diff --git a/diff.h b/diff.h
> index 5be1ee77a7..8483ca0991 100644
> --- a/diff.h
> +++ b/diff.h
> @@ -148,9 +148,9 @@ struct diff_options {
>  	int abbrev;
>  	int ita_invisible_in_index;
>  /* white-space error highlighting */
> -#define WSEH_NEW 1
> -#define WSEH_CONTEXT 2
> -#define WSEH_OLD 4
> +#define WSEH_NEW (1<<12)
> +#define WSEH_CONTEXT (1<<13)
> +#define WSEH_OLD (1<<14)

Hopefully this is a safe conversion, as everything should come from
parse_ws_error_highlight() that uses these constants.

But this is brittle; there must be some hint to future readers of
this code why these bits begin at 12th (it is linked to 07777 we saw
earlier); otherwise when they change something that needs to widen
that 07777, they will forget to shift these up, which would screw
up everything that is carefully laid out here.