diff: refactor output of incomplete line

Create a helper function that reacts to "\ No newline at the end of
file" in preparation for unifying the incomplete line handling in
the code path that handles xdiff output and the code path that
bypasses xdiff and produces a complete-rewrite patch.

Currently the output from the DIFF_SYMBOL_CONTEXT_INCOMPLETE case
still (ab)uses the same code as what is used for context lines, but
that would change in a later step where we introduce support to treat
an incomplete line as a whitespace error.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: gitster

diff.c

@@ -1379,6 +1379,10 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
 		emit_line(o, "", "", line, len);
 		break;
 	case DIFF_SYMBOL_CONTEXT_INCOMPLETE:
+		set = diff_get_color_opt(o, DIFF_CONTEXT);
+		reset = diff_get_color_opt(o, DIFF_RESET);
+		emit_line(o, set, reset, line, len);
+		break;
 	case DIFF_SYMBOL_CONTEXT_MARKER:
 		context = diff_get_color_opt(o, DIFF_CONTEXT);
 		reset = diff_get_color_opt(o, DIFF_RESET);
@@ -1668,6 +1672,13 @@ static void emit_context_line(struct emit_callback *ecbdata,
 	emit_diff_symbol(ecbdata->opt, DIFF_SYMBOL_CONTEXT, line, len, flags);
 }
 
+static void emit_incomplete_line_marker(struct emit_callback *ecbdata,
+					const char *line, int len)
+{
+	emit_diff_symbol(ecbdata->opt, DIFF_SYMBOL_CONTEXT_INCOMPLETE,
+			 line, len, 0);
+}
+
 static void emit_hunk_header(struct emit_callback *ecbdata,
 			     const char *line, int len)
 {
@@ -2437,8 +2448,7 @@ static int fn_out_consume(void *priv, char *line, unsigned long len)
 			    ecbdata->last_line_kind);
 		}
 		ecbdata->lno_in_preimage++;
-		emit_diff_symbol(o, DIFF_SYMBOL_CONTEXT_INCOMPLETE,
-				 line, len, 0);
+		emit_incomplete_line_marker(ecbdata, line, len);
 		break;
 	default:
 		BUG("fn_out_consume: unknown line '%s'", line);