git: ad488c9793fd - stable/12 - grep: fix -A handling in conjunction with -m match limitation

[Kyle Evans]

The branch stable/12 has been updated by kevans:

URL: https://cgit.FreeBSD.org/src/commit/?id=ad488c9793fd5040f8267620f370f319df31af2d

commit ad488c9793fd5040f8267620f370f319df31af2d
Author:     Kyle Evans <kevans at FreeBSD.org>
AuthorDate: 2021-02-08 18:31:17 +0000
Commit:     Kyle Evans <kevans at FreeBSD.org>
CommitDate: 2021-02-11 15:20:26 +0000

    grep: fix -A handling in conjunction with -m match limitation
    
    The basic issue here is that grep, when given -m 1, would stop all
    line processing once it hit the match count and exit immediately.  The
    problem with exiting immediately is that -A processing only happens when
    subsequent lines are processed and do not match.
    
    The fix here is relatively easy; when bsdgrep matches a line, it resets
    the 'tail' of the matching context to the value supplied to -A and
    dumps anything that's been queued up for -B. After the current line has
    been printed and tail is reset, we check our mcount and do what's
    needed. Therefore, at the time that we decide we're doing nothing, we
    know that 'tail' of the context is correct and we can simply continue
    on if there's still more to pick up.
    
    With this change, we still bail out immediately if there's been no -A
    flag. If -A was supplied, we signal that we should continue on. However,
    subsequent lines will not even bothere to try and process the line.  We
    have reached the match count, so even if the next line would match then
    we must process it if it hadn't. Thus, the loop in procfile() can
    short-circuit and just process the line as a non-match until
    procmatches() indicates that it's safe to stop.
    
    A test has been added to reflect both that we should be picking up the
    next line and that the next line should be considered a non-match even
    if it should have been.
    
    PR:             253350
    
    (cherry picked from commit 3e2d96ac974db823255a6f40b90eeffa6e38d022)
---
 contrib/netbsd-tests/usr.bin/grep/t_grep.sh | 17 +++++++++++++++++
 usr.bin/grep/util.c                         | 21 ++++++++++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/contrib/netbsd-tests/usr.bin/grep/t_grep.sh b/contrib/netbsd-tests/usr.bin/grep/t_grep.sh
index ef3f0617465e..d2539a8250de 100755
--- a/contrib/netbsd-tests/usr.bin/grep/t_grep.sh
+++ b/contrib/netbsd-tests/usr.bin/grep/t_grep.sh
@@ -907,6 +907,22 @@ mflag_body()
 	atf_check -o inline:"test1:2\n" grep -m 2 -EHc "a|b|e|f" test1
 }
 
+atf_test_case mflag_trail_ctx
+mflag_trail_ctx_head()
+{
+	atf_set "descr" "Check proper handling of -m with trailing context (PR 253350)"
+}
+mflag_trail_ctx_body()
+{
+	printf "foo\nfoo\nbar\nfoo\nbar\nfoo\nbar\n" > test1
+
+	# Should pick up the next line after matching the first.
+	atf_check -o inline:"foo\nfoo\n" grep -A1 -m1 foo test1
+
+	# Make sure the trailer is picked up as a non-match!
+	atf_check -o inline:"1:foo\n2-foo\n" grep -A1 -nm1 foo test1
+}
+
 atf_test_case zgrep_multiple_files
 zgrep_multiple_files_head()
 {
@@ -978,6 +994,7 @@ atf_init_test_cases()
 	atf_add_test_case fgrep_oflag
 	atf_add_test_case cflag
 	atf_add_test_case mflag
+	atf_add_test_case mflag_trail_ctx
 	atf_add_test_case zgrep_multiple_files
 # End FreeBSD
 }
diff --git a/usr.bin/grep/util.c b/usr.bin/grep/util.c
index f2d845c97fed..220ffaef7dab 100644
--- a/usr.bin/grep/util.c
+++ b/usr.bin/grep/util.c
@@ -250,6 +250,16 @@ static bool
 procmatches(struct mprintc *mc, struct parsec *pc, bool matched)
 {
 
+	if (mflag && mcount <= 0) {
+		/*
+		 * We already hit our match count, but we need to keep dumping
+		 * lines until we've lost our tail.
+		 */
+		grep_printline(&pc->ln, '-');
+		mc->tail--;
+		return (mc->tail != 0);
+	}
+
 	/*
 	 * XXX TODO: This should loop over pc->matches and handle things on a
 	 * line-by-line basis, setting up a `struct str` as needed.
@@ -263,7 +273,7 @@ procmatches(struct mprintc *mc, struct parsec *pc, bool matched)
 			/* XXX TODO: Decrement by number of matched lines */
 			mcount -= 1;
 			if (mcount <= 0)
-				return (false);
+				return (mc->tail != 0);
 		}
 	} else if (mc->doctx)
 		procmatch_nomatch(mc, pc);
@@ -355,6 +365,15 @@ procfile(const char *fn)
 			return (0);
 		}
 
+		if (mflag && mcount <= 0) {
+			/*
+			 * Short-circuit, already hit match count and now we're
+			 * just picking up any remaining pieces.
+			 */
+			if (!procmatches(&mc, &pc, false))
+				break;
+			continue;
+		}
 		line_matched = procline(&pc) == !vflag;
 		if (line_matched)
 			++lines;