From 467babf8d059caee9587567452fc8b46505b4e67 Mon Sep 17 00:00:00 2001
From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 3 Sep 2009 23:39:43 -0700
Subject: [PATCH] diff --whitespace=warn/error: fix blank-at-eof check

The "diff --check" logic used to share the same issue as the one fixed for
"git apply" earlier in this series, in that a patch that adds new blank
lines at end could appear as

    @@ -l,5 +m,7 @@$
    _context$
    _context$
    -deleted$
    +$
    +$
    +$
    _$
    _$

where _ stands for SP and $ shows a end-of-line.  Instead of looking at
each line in the patch in the callback, simply count the blank lines from
the end in two versions, and notice the presence of new ones.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 diff.c                     | 64 ++++++++++++++++++++++++++++----------
 t/t4015-diff-whitespace.sh |  7 +++++
 2 files changed, 55 insertions(+), 16 deletions(-)

diff --git a/diff.c b/diff.c
index a693d184c..c19c4760f 100644
--- a/diff.c
+++ b/diff.c
@@ -1149,7 +1149,6 @@ struct checkdiff_t {
 	struct diff_options *o;
 	unsigned ws_rule;
 	unsigned status;
-	int trailing_blanks_start;
 };
 
 static int is_conflict_marker(const char *line, unsigned long len)
@@ -1193,10 +1192,6 @@ static void checkdiff_consume(void *priv, char *line, unsigned long len)
 	if (line[0] == '+') {
 		unsigned bad;
 		data->lineno++;
-		if (!ws_blank_line(line + 1, len - 1, data->ws_rule))
-			data->trailing_blanks_start = 0;
-		else if (!data->trailing_blanks_start)
-			data->trailing_blanks_start = data->lineno;
 		if (is_conflict_marker(line + 1, len - 1)) {
 			data->status |= 1;
 			fprintf(data->o->file,
@@ -1216,14 +1211,12 @@ static void checkdiff_consume(void *priv, char *line, unsigned long len)
 			      data->o->file, set, reset, ws);
 	} else if (line[0] == ' ') {
 		data->lineno++;
-		data->trailing_blanks_start = 0;
 	} else if (line[0] == '@') {
 		char *plus = strchr(line, '+');
 		if (plus)
 			data->lineno = strtol(plus, NULL, 10) - 1;
 		else
 			die("invalid diff");
-		data->trailing_blanks_start = 0;
 	}
 }
 
@@ -1437,6 +1430,44 @@ static const struct funcname_pattern_entry *diff_funcname_pattern(struct diff_fi
 	return NULL;
 }
 
+static int count_trailing_blank(mmfile_t *mf, unsigned ws_rule)
+{
+	char *ptr = mf->ptr;
+	long size = mf->size;
+	int cnt = 0;
+
+	if (!size)
+		return cnt;
+	ptr += size - 1; /* pointing at the very end */
+	if (*ptr != '\n')
+		; /* incomplete line */
+	else
+		ptr--; /* skip the last LF */
+	while (mf->ptr < ptr) {
+		char *prev_eol;
+		for (prev_eol = ptr; mf->ptr <= prev_eol; prev_eol--)
+			if (*prev_eol == '\n')
+				break;
+		if (!ws_blank_line(prev_eol + 1, ptr - prev_eol, ws_rule))
+			break;
+		cnt++;
+		ptr = prev_eol - 1;
+	}
+	return cnt;
+}
+
+static int adds_blank_at_eof(mmfile_t *mf1, mmfile_t *mf2, unsigned ws_rule)
+{
+	int l1, l2, at;
+	l1 = count_trailing_blank(mf1, ws_rule);
+	l2 = count_trailing_blank(mf2, ws_rule);
+	if (l2 <= l1)
+		return 0;
+	/* starting where? */
+	at = count_lines(mf1->ptr, mf1->size);
+	return (at - l1) + 1; /* the line number counts from 1 */
+}
+
 static void builtin_diff(const char *name_a,
 			 const char *name_b,
 			 struct diff_filespec *one,
@@ -1650,15 +1681,16 @@ static void builtin_checkdiff(const char *name_a, const char *name_b,
 		ecb.priv = &data;
 		xdi_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
 
-		if ((data.ws_rule & WS_BLANK_AT_EOF) &&
-		    data.trailing_blanks_start) {
-			static char *err;
-
-			if (!err)
-				err = whitespace_error_string(WS_BLANK_AT_EOF);
-			fprintf(o->file, "%s:%d: %s\n",
-				data.filename, data.trailing_blanks_start, err);
-			data.status = 1; /* report errors */
+		if (data.ws_rule & WS_BLANK_AT_EOF) {
+			int blank_at_eof = adds_blank_at_eof(&mf1, &mf2, data.ws_rule);
+			if (blank_at_eof) {
+				static char *err;
+				if (!err)
+					err = whitespace_error_string(WS_BLANK_AT_EOF);
+				fprintf(o->file, "%s:%d: %s.\n",
+					data.filename, blank_at_eof, err);
+				data.status = 1; /* report errors */
+			}
 		}
 	}
  free_and_return:
diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index a5d446157..e0b481d42 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -341,6 +341,13 @@ test_expect_success 'checkdiff detects new trailing blank lines (1)' '
 	git diff --check | grep "new blank line"
 '
 
+test_expect_success 'checkdiff detects new trailing blank lines (2)' '
+	{ echo a; echo b; echo; echo; } >x &&
+	git add x &&
+	{ echo a; echo; echo; echo; echo; } >x &&
+	git diff --check | grep "new blank line"
+'
+
 test_expect_success 'checkdiff allows new blank lines' '
 	git checkout x &&
 	mv x y &&
-- 
2.30.2