builtin/am: allow disabling conflict advice

When 'git am' or 'git rebase --apply' encounter a conflict, they show a
message instructing the user how to continue the operation. This message
can't be disabled.

Use ADVICE_MERGE_CONFLICT introduced in the previous commit to allow
disabling it. Update the tests accordingly, as the advice output is now
on stderr instead of stdout. In t4150, redirect stdout to 'out' and
stderr to 'err', since this is less confusing. In t4254, as we are
testing a specific failure mode of 'git am', simply disable the advice.
Note that we are not testing that this advice is shown in 'git rebase'
for the apply backend since 2ac0d62 (rebase: change the default
backend from "am" to "merge", 2020-02-15).

Helped-by: Phillip Wood <[email protected]>
Helped-by: Junio C Hamano <[email protected]>
Signed-off-by: Philippe Blain <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: phil-blain

builtin/am.c

@@ -1150,19 +1150,23 @@ static const char *msgnum(const struct am_state *state)
 static void NORETURN die_user_resolve(const struct am_state *state)
 {
 	if (state->resolvemsg) {
-		printf_ln("%s", state->resolvemsg);
+		advise_if_enabled(ADVICE_MERGE_CONFLICT, "%s", state->resolvemsg);
 	} else {
 		const char *cmdline = state->interactive ? "git am -i" : "git am";
+		struct strbuf sb = STRBUF_INIT;
 
-		printf_ln(_("When you have resolved this problem, run \"%s --continue\"."), cmdline);
-		printf_ln(_("If you prefer to skip this patch, run \"%s --skip\" instead."), cmdline);
+		strbuf_addf(&sb, _("When you have resolved this problem, run \"%s --continue\".\n"), cmdline);
+		strbuf_addf(&sb, _("If you prefer to skip this patch, run \"%s --skip\" instead.\n"), cmdline);
 
 		if (advice_enabled(ADVICE_AM_WORK_DIR) &&
 		    is_empty_or_missing_file(am_path(state, "patch")) &&
 		    !repo_index_has_changes(the_repository, NULL, NULL))
-			printf_ln(_("To record the empty patch as an empty commit, run \"%s --allow-empty\"."), cmdline);
+			strbuf_addf(&sb, _("To record the empty patch as an empty commit, run \"%s --allow-empty\".\n"), cmdline);
 
-		printf_ln(_("To restore the original branch and stop patching, run \"%s --abort\"."), cmdline);
+		strbuf_addf(&sb, _("To restore the original branch and stop patching, run \"%s --abort\"."), cmdline);
+
+		advise_if_enabled(ADVICE_MERGE_CONFLICT, "%s", sb.buf);
+		strbuf_release(&sb);
 	}
 
 	exit(128);

t/t4150-am.sh

@@ -1224,8 +1224,8 @@ test_expect_success 'record as an empty commit when meeting e-mail message that
 
 test_expect_success 'skip an empty patch in the middle of an am session' '
 	git checkout empty-commit^ &&
-	test_must_fail git am empty-commit.patch >err &&
-	grep "Patch is empty." err &&
+	test_must_fail git am empty-commit.patch >out 2>err &&
+	grep "Patch is empty." out &&
 	grep "To record the empty patch as an empty commit, run \"git am --allow-empty\"." err &&
 	git am --skip &&
 	test_path_is_missing .git/rebase-apply &&
@@ -1236,8 +1236,8 @@ test_expect_success 'skip an empty patch in the middle of an am session' '
 
 test_expect_success 'record an empty patch as an empty commit in the middle of an am session' '
 	git checkout empty-commit^ &&
-	test_must_fail git am empty-commit.patch >err &&
-	grep "Patch is empty." err &&
+	test_must_fail git am empty-commit.patch >out 2>err &&
+	grep "Patch is empty." out &&
 	grep "To record the empty patch as an empty commit, run \"git am --allow-empty\"." err &&
 	git am --allow-empty >output &&
 	grep "No changes - recorded it as an empty commit." output &&

t/t4254-am-corrupt.sh

@@ -59,7 +59,7 @@ test_expect_success setup '
 # Also, it had the unwanted side-effect of deleting f.
 test_expect_success 'try to apply corrupted patch' '
 	test_when_finished "git am --abort" &&
-	test_must_fail git -c advice.amWorkDir=false am bad-patch.diff 2>actual &&
+	test_must_fail git -c advice.amWorkDir=false -c advice.mergeConflict=false am bad-patch.diff 2>actual &&
 	echo "error: git diff header lacks filename information (line 4)" >expected &&
 	test_path_is_file f &&
 	test_cmp expected actual