[PATCH v2 09/10] ref-filter.c: use peeled tag for '*' format fields

["Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com>]

From: Victoria Dye <vdye@github.com>

In most builtins ('rev-parse <revision>^{}', 'show-ref --dereference'),
"dereferencing" a tag refers to a recursive peel of the tag object. Unlike
these cases, the dereferencing prefix ('*') in 'for-each-ref' format
specifiers triggers only a single, non-recursive dereference of a given tag
object. For most annotated tags, a single dereference is all that is needed
to access the tag's associated commit or tree; "recursive" and
"non-recursive" dereferencing are functionally equivalent in these cases.
However, nested tags (annotated tags whose target is another annotated tag)
dereferenced once return another tag, where a recursive dereference would
return the commit or tree.

Currently, if a user wants to filter & format refs and include information
about a recursively-dereferenced tag, they can do so with something like
'cat-file --batch-check':

    git for-each-ref --format="%(objectname)^{} %(refname)" <pattern> |
        git cat-file --batch-check="%(objectname) %(rest)"

But the combination of commands is inefficient. So, to improve the
performance of this use case and align the defererencing behavior of
'for-each-ref' with that of other commands, update the ref formatting code
to use the peeled tag (from 'peel_iterated_oid()') to populate '*' fields
rather than the tag's immediate target object (from 'get_tagged_oid()').

Additionally, add a test to 't6300-for-each-ref' to verify new nested tag
behavior and update 't6302-for-each-ref-filter.sh' to print the correct
value for nested dereferenced fields.

Signed-off-by: Victoria Dye <vdye@github.com>
---
 Documentation/git-for-each-ref.txt |  4 ++--
 ref-filter.c                       | 13 ++++---------
 t/t6300-for-each-ref.sh            | 22 ++++++++++++++++++++++
 t/t6302-for-each-ref-filter.sh     |  4 ++--
 4 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
index b136c9fa908..be9543f6840 100644
--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt
@@ -296,8 +296,8 @@ from the `committer` or `tagger` fields depending on the object type.
 These are intended for working on a mix of annotated and lightweight tags.
 
 For tag objects, a `fieldname` prefixed with an asterisk (`*`) expands to
-the `fieldname` value of object the tag points at, rather than that of the
-tag object itself.
+the `fieldname` value of the peeled object, rather than that of the tag
+object itself.
 
 Fields that have name-email-date tuple as its value (`author`,
 `committer`, and `tagger`) can be suffixed with `name`, `email`,
diff --git a/ref-filter.c b/ref-filter.c
index 48453db24f7..fdaabb5bb45 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -2508,17 +2508,12 @@ static int populate_value(struct ref_array_item *ref, struct strbuf *err)
 		return 0;
 
 	/*
-	 * If it is a tag object, see if we use a value that derefs
-	 * the object, and if we do grab the object it refers to.
+	 * If it is a tag object, see if we use the peeled value. If we do,
+	 * grab the peeled OID.
 	 */
-	oi_deref.oid = *get_tagged_oid((struct tag *)obj);
+	if (need_tagged && peel_iterated_oid(&obj->oid, &oi_deref.oid))
+		die("bad tag");
 
-	/*
-	 * NEEDSWORK: This derefs tag only once, which
-	 * is good to deal with chains of trust, but
-	 * is not consistent with what deref_tag() does
-	 * which peels the onion to the core.
-	 */
 	return get_object(ref, 1, &obj, &oi_deref, err);
 }
 
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index 0613e5e3623..54e22812598 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -1839,6 +1839,28 @@ test_expect_success 'git for-each-ref with non-existing refs' '
 	test_must_be_empty actual
 '
 
+test_expect_success 'git for-each-ref with nested tags' '
+	git tag -am "Normal tag" nested/base HEAD &&
+	git tag -am "Nested tag" nested/nest1 refs/tags/nested/base &&
+	git tag -am "Double nested tag" nested/nest2 refs/tags/nested/nest1 &&
+
+	head_oid="$(git rev-parse HEAD)" &&
+	base_tag_oid="$(git rev-parse refs/tags/nested/base)" &&
+	nest1_tag_oid="$(git rev-parse refs/tags/nested/nest1)" &&
+	nest2_tag_oid="$(git rev-parse refs/tags/nested/nest2)" &&
+
+	cat >expect <<-EOF &&
+	refs/tags/nested/base $base_tag_oid tag $head_oid commit
+	refs/tags/nested/nest1 $nest1_tag_oid tag $head_oid commit
+	refs/tags/nested/nest2 $nest2_tag_oid tag $head_oid commit
+	EOF
+
+	git for-each-ref \
+		--format="%(refname) %(objectname) %(objecttype) %(*objectname) %(*objecttype)" \
+		refs/tags/nested/ >actual &&
+	test_cmp expect actual
+'
+
 GRADE_FORMAT="%(signature:grade)%0a%(signature:key)%0a%(signature:signer)%0a%(signature:fingerprint)%0a%(signature:primarykeyfingerprint)"
 TRUSTLEVEL_FORMAT="%(signature:trustlevel)%0a%(signature:key)%0a%(signature:signer)%0a%(signature:fingerprint)%0a%(signature:primarykeyfingerprint)"
 
diff --git a/t/t6302-for-each-ref-filter.sh b/t/t6302-for-each-ref-filter.sh
index af223e44d67..82f3d1ea0f2 100755
--- a/t/t6302-for-each-ref-filter.sh
+++ b/t/t6302-for-each-ref-filter.sh
@@ -45,8 +45,8 @@ test_expect_success 'check signed tags with --points-at' '
 	sed -e "s/Z$//" >expect <<-\EOF &&
 	refs/heads/side Z
 	refs/tags/annotated-tag four
-	refs/tags/doubly-annotated-tag An annotated tag
-	refs/tags/doubly-signed-tag A signed tag
+	refs/tags/doubly-annotated-tag four
+	refs/tags/doubly-signed-tag four
 	refs/tags/four Z
 	refs/tags/signed-tag four
 	EOF
-- 
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