[PATCH 1/3] refs: allow "HEAD" as decoration filter

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

The normalize_glob_ref() method was introduced in 65516f586b693 (log:
add option to choose which refs to decorate, 2017-11-21) to help with
decoration filters such as --decorate-refs=<filter> and
--decorate-refs-exclude=<filter>. The method has not been used anywhere
else.

At the moment, it is impossible to specify HEAD as a decoration filter
since normalize_glob_ref() prepends "refs/" to the filter if it isn't
already there.

Allow adding HEAD as a decoration filter by allowing the exact string
"HEAD" to not be prepended with "refs/". Add a test in t4202-log.sh that
would previously fail since the HEAD decoration would exist in the
output.

It is sufficient to only cover "HEAD" here and not include other special
refs like REBASE_HEAD. This is because HEAD is the only ref outside of
refs/* that is added to the list of decorations.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 refs.c         | 4 ++--
 t/t4202-log.sh | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/refs.c b/refs.c
index 90bcb271687..ec3134e4842 100644
--- a/refs.c
+++ b/refs.c
@@ -457,8 +457,8 @@ void normalize_glob_ref(struct string_list_item *item, const char *prefix,
 
 	if (prefix) {
 		strbuf_addstr(&normalized_pattern, prefix);
-	}
-	else if (!starts_with(pattern, "refs/"))
+	} else if (!starts_with(pattern, "refs/") &&
+		   strcmp(pattern, "HEAD"))
 		strbuf_addstr(&normalized_pattern, "refs/");
 	strbuf_addstr(&normalized_pattern, pattern);
 	strbuf_strip_suffix(&normalized_pattern, "/");
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 6e663525582..6b7d8e269f7 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -1025,6 +1025,12 @@ test_expect_success 'decorate-refs and simplify-by-decoration without output' '
 	test_cmp expect actual
 '
 
+test_expect_success 'decorate-refs-exclude HEAD' '
+	git log --decorate=full --oneline \
+		--decorate-refs-exclude="HEAD" >actual &&
+	! grep HEAD actual
+'
+
 test_expect_success 'log.decorate config parsing' '
 	git log --oneline --decorate=full >expect.full &&
 	git log --oneline --decorate=short >expect.short &&
-- 
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