[PATCH 2/8] ahead-behind: parse tip references

["Derrick Stolee via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Derrick Stolee <derrickstolee@xxxxxxxxxx>

Before implementing the logic to compute the ahead/behind counts, parse
the unknown options as commits and place them in a string_list.

Be sure to error out when the reference is not found.

Co-authored-by: Taylor Blau <me@xxxxxxxxxxxx>
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
Signed-off-by: Derrick Stolee <derrickstolee@xxxxxxxxxx>
---
 builtin/ahead-behind.c  | 39 +++++++++++++++++++++++++++++++++++++++
 t/t4218-ahead-behind.sh | 10 ++++++++++
 2 files changed, 49 insertions(+)

diff --git a/builtin/ahead-behind.c b/builtin/ahead-behind.c
index a56cc565def..c1212cc8d46 100644
--- a/builtin/ahead-behind.c
+++ b/builtin/ahead-behind.c
@@ -1,16 +1,31 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "config.h"
+#include "commit.h"
 
 static const char * const ahead_behind_usage[] = {
 	N_("git ahead-behind --base=<ref> [ --stdin | <revs> ]"),
 	NULL
 };
 
+static int handle_arg(struct string_list *tips, const char *arg)
+{
+	struct string_list_item *item;
+	struct commit *c = lookup_commit_reference_by_name(arg);
+
+	if (!c)
+		return error(_("could not resolve '%s'"), arg);
+
+	item = string_list_append(tips, arg);
+	item->util = c;
+	return 0;
+}
+
 int cmd_ahead_behind(int argc, const char **argv, const char *prefix)
 {
 	const char *base_ref = NULL;
 	int from_stdin = 0;
+	struct string_list tips = STRING_LIST_INIT_DUP;
 
 	struct option ahead_behind_opts[] = {
 		OPT_STRING('b', "base", &base_ref, N_("base"), N_("base reference to process")),
@@ -26,5 +41,29 @@ int cmd_ahead_behind(int argc, const char **argv, const char *prefix)
 
 	git_config(git_default_config, NULL);
 
+	if (from_stdin) {
+		struct strbuf line = STRBUF_INIT;
+
+		while (strbuf_getline(&line, stdin) != EOF) {
+			if (!line.len)
+				break;
+
+			if (handle_arg(&tips, line.buf))
+				return 1;
+		}
+
+		strbuf_release(&line);
+	} else {
+		int i;
+		for (i = 0; i < argc; ++i) {
+			if (handle_arg(&tips, argv[i]))
+				return 1;
+		}
+	}
+
+	/* Early return for no tips. */
+	if (!tips.nr)
+		return 0;
+
 	return 0;
 }
diff --git a/t/t4218-ahead-behind.sh b/t/t4218-ahead-behind.sh
index bc08f1207a0..3b8b9dc9887 100755
--- a/t/t4218-ahead-behind.sh
+++ b/t/t4218-ahead-behind.sh
@@ -14,4 +14,14 @@ test_expect_success 'git ahead-behind without --base' '
 	grep "usage:" err
 '
 
+test_expect_success 'git ahead-behind with broken tip' '
+	test_must_fail git ahead-behind --base=HEAD bogus 2>err &&
+	grep "could not resolve '\''bogus'\''" err
+'
+
+test_expect_success 'git ahead-behind without tips' '
+	git ahead-behind --base=HEAD 2>err &&
+	test_must_be_empty err
+'
+
 test_done
-- 
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