ref-filter.c: use peeled tag for '*' format fields

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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
index f64fa8b406..9fa98e5872 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`,