dir-iterator: add flags parameter to dir_iterator_begin

Add the possibility of giving flags to dir_iterator_begin to initialize
a dir-iterator with special options.

Currently possible flags are:
- DIR_ITERATOR_PEDANTIC, which makes dir_iterator_advance abort
immediately in the case of an error, instead of keep looking for the
next valid entry;
- DIR_ITERATOR_FOLLOW_SYMLINKS, which makes the iterator follow
symlinks and include linked directories' contents in the iteration.

These new flags will be used in a subsequent patch.

Also add tests for the flags' usage and adjust refs/files-backend.c to
the new dir_iterator_begin signature.

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t0066-dir-iterator.sh b/t/t0066-dir-iterator.sh
index cc4b19c..9354d3f 100755
--- a/t/t0066-dir-iterator.sh
+++ b/t/t0066-dir-iterator.sh
@@ -65,4 +65,84 @@
 	test_cmp expected-non-dir-output actual-non-dir-output
 '
 
+test_expect_success POSIXPERM,SANITY 'advance should not fail on errors by default' '
+	cat >expected-no-permissions-output <<-EOF &&
+	[d] (a) [a] ./dir3/a
+	EOF
+
+	mkdir -p dir3/a &&
+	>dir3/a/b &&
+	chmod 0 dir3/a &&
+
+	test-tool dir-iterator ./dir3 >actual-no-permissions-output &&
+	test_cmp expected-no-permissions-output actual-no-permissions-output &&
+	chmod 755 dir3/a &&
+	rm -rf dir3
+'
+
+test_expect_success POSIXPERM,SANITY 'advance should fail on errors, w/ pedantic flag' '
+	cat >expected-no-permissions-pedantic-output <<-EOF &&
+	[d] (a) [a] ./dir3/a
+	dir_iterator_advance failure
+	EOF
+
+	mkdir -p dir3/a &&
+	>dir3/a/b &&
+	chmod 0 dir3/a &&
+
+	test_must_fail test-tool dir-iterator --pedantic ./dir3 \
+		>actual-no-permissions-pedantic-output &&
+	test_cmp expected-no-permissions-pedantic-output \
+		actual-no-permissions-pedantic-output &&
+	chmod 755 dir3/a &&
+	rm -rf dir3
+'
+
+test_expect_success SYMLINKS 'setup dirs with symlinks' '
+	mkdir -p dir4/a &&
+	mkdir -p dir4/b/c &&
+	>dir4/a/d &&
+	ln -s d dir4/a/e &&
+	ln -s ../b dir4/a/f &&
+
+	mkdir -p dir5/a/b &&
+	mkdir -p dir5/a/c &&
+	ln -s ../c dir5/a/b/d &&
+	ln -s ../ dir5/a/b/e &&
+	ln -s ../../ dir5/a/b/f
+'
+
+test_expect_success SYMLINKS 'dir-iterator should not follow symlinks by default' '
+	cat >expected-no-follow-sorted-output <<-EOF &&
+	[d] (a) [a] ./dir4/a
+	[d] (b) [b] ./dir4/b
+	[d] (b/c) [c] ./dir4/b/c
+	[f] (a/d) [d] ./dir4/a/d
+	[s] (a/e) [e] ./dir4/a/e
+	[s] (a/f) [f] ./dir4/a/f
+	EOF
+
+	test-tool dir-iterator ./dir4 >out &&
+	sort out >actual-no-follow-sorted-output &&
+
+	test_cmp expected-no-follow-sorted-output actual-no-follow-sorted-output
+'
+
+test_expect_success SYMLINKS 'dir-iterator should follow symlinks w/ follow flag' '
+	cat >expected-follow-sorted-output <<-EOF &&
+	[d] (a) [a] ./dir4/a
+	[d] (a/f) [f] ./dir4/a/f
+	[d] (a/f/c) [c] ./dir4/a/f/c
+	[d] (b) [b] ./dir4/b
+	[d] (b/c) [c] ./dir4/b/c
+	[f] (a/d) [d] ./dir4/a/d
+	[f] (a/e) [e] ./dir4/a/e
+	EOF
+
+	test-tool dir-iterator --follow-symlinks ./dir4 >out &&
+	sort out >actual-follow-sorted-output &&
+
+	test_cmp expected-follow-sorted-output actual-follow-sorted-output
+'
+
 test_done