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Fix "git apply" to correctly enforce "match at the beginning"

An earlier commit 4be6096 (apply --unidiff-zero: loosen sanity checks for --unidiff=0 patches, 2006-09-17) made match_beginning and match_end computed incorrectly. If a hunk inserts at the beginning, old position recorded at the hunk is line 0, and if a hunk changes at the beginning, it is line 1. The new test added to t4104 exposes that the old code did not insist on matching at the beginning for a patch to add a line to an empty file. An even older 65aadb9 (apply: force matching at the beginning., 2006-05-24) was equally wrong in that it tried to take hints from the number of leading context lines, to decide if the hunk must match at the beginning, but we can just look at the line number in the hunk to decide. Signed-off-by: Junio C Hamano <gitster@pobox.com>

Junio C Hamano committed Apr 6, 2008 at 19:21 UTC ee5a317e0130ab2db59db97c644576335530512d
2 files changed +29 -13
builtin-apply.c
+16 -13
@@ -1736,21 +1736,24 @@ static int apply_one_fragment(struct strbuf *buf, struct fragment *frag,
1736 trailing = frag->trailing;
1737
1738 /*
1739 - * If we don't have any leading/trailing data in the patch,
1740 - * we want it to match at the beginning/end of the file.
1739 + * A hunk to change lines at the beginning would begin with
1740 + * @@ -1,L +N,M @@
1741 *
1742 - * But that would break if the patch is generated with
1743 - * --unified=0; sane people wouldn't do that to cause us
1744 - * trouble, but we try to please not so sane ones as well.
1742 + * And a hunk to add to an empty file would begin with
1743 + * @@ -0,0 +N,M @@
1744 + *
1745 + * In other words, a hunk that is (frag->oldpos <= 1) with or
1746 + * without leading context must match at the beginning.
1747 */
1746 - if (unidiff_zero) {
1747 - match_beginning = (!leading && !frag->oldpos);
1748 - match_end = 0;
1749 - }
1750 - else {
1751 - match_beginning = !leading && (frag->oldpos == 1);
1752 - match_end = !trailing;
1753 - }
1748 + match_beginning = frag->oldpos <= 1;
1749 +
1750 + /*
1751 + * A hunk without trailing lines must match at the end.
1752 + * However, we simply cannot tell if a hunk must match end
1753 + * from the lack of trailing lines if the patch was generated
1754 + * with unidiff without any context.
1755 + */
1756 + match_end = !unidiff_zero && !trailing;
1757
1758 lines = 0;
1759 pos = frag->newpos;
t/t4104-apply-boundary.sh
+13
@@ -112,4 +112,17 @@ do
112 '
113 done
114
115 +test_expect_success 'two lines' '
116 +
117 + >file &&
118 + git add file &&
119 + echo aaa >file &&
120 + git diff >patch &&
121 + git add file &&
122 + echo bbb >file &&
123 + git add file &&
124 + test_must_fail git apply --check patch
125 +
126 +'
127 +
128 test_done