bisect--helper: use BISECT_TERMS in 'bisect skip' command

Commit e4c7b33 ("bisect--helper: reimplement `bisect_skip` shell
function in C", 2021-02-03), as part of the shell-to-C conversion,
forgot to read the 'terms' file (.git/BISECT_TERMS) during the new
'bisect skip' command implementation. As a result, the 'bisect skip'
command will use the default 'bad'/'good' terms. If the bisection
terms have been set to non-default values (for example by the
'bisect start' command), then the 'bisect skip' command will fail.

In order to correct this problem, we insert a call to the get_terms()
function, which reads the non-default terms from that file (if set),
in the '--bisect-skip' command implementation of 'bisect--helper'.

Also, add a test[1] to protect against potential future regression.

[1] https://lore.kernel.org/git/[email protected]/T/#m207791568054b0f8cf1a3942878ea36293273c7d

Reported-by: Trygve Aaberge <[email protected]>
Signed-off-by: Bagas Sanjaya <[email protected]>
Signed-off-by: Ramsay Jones <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ramsay-jones

builtin/bisect--helper.c

@@ -1126,6 +1126,7 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 		break;
 	case BISECT_SKIP:
 		set_terms(&terms, "bad", "good");
+		get_terms(&terms);
 		res = bisect_skip(&terms, argv, argc);
 		break;
 	default:

t/t6030-bisect-porcelain.sh

@@ -922,6 +922,17 @@ test_expect_success 'bisect start takes options and revs in any order' '
 	test_cmp expected actual
 '
 
+# Bisect is started with --term-new and --term-old arguments,
+# then skip. The HEAD should be changed.
+test_expect_success 'bisect skip works with --term*' '
+	git bisect reset &&
+	git bisect start --term-new=fixed --term-old=unfixed HEAD $HASH1 &&
+	hash_skipped_from=$(git rev-parse --verify HEAD) &&
+	git bisect skip &&
+	hash_skipped_to=$(git rev-parse --verify HEAD) &&
+	test "$hash_skipped_from" != "$hash_skipped_to"
+'
+
 test_expect_success 'git bisect reset cleans bisection state properly' '
 	git bisect reset &&
 	git bisect start &&