refs: improve handling of special refs

Hi,

this is the third version of my patch series to improve handling of special refs.

Changes combpared to v2:

- Patch 1: We're now more careful around missing and symbolic refs.

- Patch 3: Document in the commit message that the extended list of special refs is not intended to stay like this forever.

Thanks for your reviews and the discussion!

Patrick

Patrick Steinhardt (4):
wt-status: read HEAD and ORIG_HEAD via the refdb
refs: propagate errno when reading special refs fails
refs: complete list of special refs
bisect: consistently write BISECT_EXPECTED_REV via the refdb

 bisect.c                    | 25 +++-------------
 builtin/bisect.c            |  8 ++---
 refs.c                      | 59 +++++++++++++++++++++++++++++++++++--
 t/t1403-show-ref.sh         | 10 +++++++
 t/t6030-bisect-porcelain.sh |  2 +-
 wt-status.c                 | 22 +++++++++-----
 6 files changed, 87 insertions(+), 39 deletions(-)

Range-diff against v2:
1: 1db3eb3945 ! 1: aea9410bd9 wt-status: read HEAD and ORIG_HEAD via the refdb
@@ Commit message
via the refdb layer so that we'll also be compatible with alternate reference backends.

- Note that we pass RESOLVE_REF_NO_RECURSE to read_ref_full(). This is
- because we didn't resolve symrefs before either, and in practice none of
- the refs in "rebase-merge/" would be symbolic. We thus don't want to
- resolve symrefs with the new code either to retain the old behaviour.
+ There are some subtleties involved here:
+
+ - We pass RESOLVE_REF_READING so that a missing ref will cause
+ read_ref_full() to return an error.
+
+ - We pass RESOLVE_REF_NO_RECURSE so that we do not try to resolve
+ symrefs. The old code didn't resolve symrefs either, and we only
+ ever write object IDs into the refs in "rebase-merge/".
+
+ - In the same spirit we verify that successfully-read refs are not
+ symbolic refs.

@@ wt-status.c: static char *read_line_from_git_path(const char *filename)
- char *head, *orig_head, *rebase_amend, *rebase_orig_head;
+ struct object_id head_oid, orig_head_oid;
+ char *rebase_amend, *rebase_orig_head;
++ int head_flags, orig_head_flags;

if ((!s->amend && !s->nowarn && !s->workdir_dirty) ||
!s->branch || strcmp(s->branch, "HEAD"))
@@ wt-status.c: static char *read_line_from_git_path(const char *filename)

- head = read_line_from_git_path("HEAD");
- orig_head = read_line_from_git_path("ORIG_HEAD");
-+ if (read_ref_full("HEAD", RESOLVE_REF_NO_RECURSE, &head_oid, NULL) ||
-+ read_ref_full("ORIG_HEAD", RESOLVE_REF_NO_RECURSE, &orig_head_oid, NULL))
++ if (read_ref_full("HEAD", RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
++ &head_oid, &head_flags) ||
++ read_ref_full("ORIG_HEAD", RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
++ &orig_head_oid, &orig_head_flags))
++ return 0;
++ if (head_flags & REF_ISSYMREF || orig_head_flags & REF_ISSYMREF)
+ return 0;
+
rebase_amend = read_line_from_git_path("rebase-merge/amend");

2:  24032a62e5 = 2:  455ab69177 refs: propagate errno when reading special refs fails
3:  3dd9089fd5 ! 3:  81ac092281 refs: complete list of special refs

@@ Commit message

We're already mostly good with regard to the first item, except for BISECT_EXPECTED_REV which will be addressed in a subsequent commit.
- But the current list of special refs is missing a lot of refs that
- really should be treated specially. Right now, we only treat
- FETCH_HEAD and MERGE_HEAD specially here.
+ But the current list of special refs is missing some refs that really
+ should be treated specially. Right now, we only treat FETCH_HEAD and
+ MERGE_HEAD specially here.

Introduce a new function is_special_ref() that contains all current instances of special refs to fix the reading path.

+ Note that this is only a temporary measure where we record and rectify
+ the current state. Ideally, the list of special refs should in the end
+ only contain FETCH_HEAD and MERGE_HEAD again because they both may
+ reference multiple objects and can contain annotations, so they indeed
+ are special.
+

4: 4a4447a3f5 = 4: 3244678161 bisect: consistently write BISECT_EXPECTED_REV via the refdb

base-commit: 1a87c842ece327d03d08096395969aca5e0a6996

2.43.GIT