prepare_revision_walk() allows callers to take ownership of the array of
pending objects by setting the rev_info flag "leak_pending" and copying
the object_array "pending".  They use it to clear commit marks after
setup is done.  This interface is brittle enough that it requires
extensive comments.

Provide an easier way by adding a function that can hand over the array
to a caller-supplied output parameter and converting all users of the
flag "leak_pending" to call prepare_revision_walk_extended() instead.

Signed-off-by: Rene Scharfe <l....@web.de>
---
 Documentation/technical/api-revision-walking.txt |  6 ++++++
 bisect.c                                         | 17 +++++------------
 builtin/checkout.c                               |  9 +--------
 bundle.c                                         |  9 +--------
 revision.c                                       | 10 +++++++++-
 revision.h                                       | 14 ++------------
 6 files changed, 24 insertions(+), 41 deletions(-)

diff --git a/Documentation/technical/api-revision-walking.txt 
b/Documentation/technical/api-revision-walking.txt
index 55b878ade8..9dc573d2ec 100644
--- a/Documentation/technical/api-revision-walking.txt
+++ b/Documentation/technical/api-revision-walking.txt
@@ -50,6 +50,12 @@ function.
        returns any error (non-zero return code) and if it does not, you can
        start using get_revision() to do the iteration.
 
+`prepare_revision_walk_extended`::
+
+       Like prepare_revision_walk(), but allows callers to take ownership
+       of the array of pending objects by passing an object_array pointer
+       as the second parameter; passing NULL clears the array.
+
 `get_revision`::
 
        Takes a pointer to a `rev_info` structure and iterates over it,
diff --git a/bisect.c b/bisect.c
index 0fca17c02b..a2af405d28 100644
--- a/bisect.c
+++ b/bisect.c
@@ -641,9 +641,10 @@ static void bisect_rev_setup(struct rev_info *revs, const 
char *prefix,
        /* XXX leak rev_argv, as "revs" may still be pointing to it */
 }
 
-static void bisect_common(struct rev_info *revs)
+static void bisect_common(struct rev_info *revs,
+                         struct object_array *old_pending_ptr)
 {
-       if (prepare_revision_walk(revs))
+       if (prepare_revision_walk_extended(revs, old_pending_ptr))
                die("revision walk setup failed");
        if (revs->tree_objects)
                mark_edges_uninteresting(revs, NULL);
@@ -825,15 +826,7 @@ static int check_ancestors(const char *prefix)
        bisect_rev_setup(&revs, prefix, "^%s", "%s", 0);
 
        /* Save pending objects, so they can be cleaned up later. */
-       pending_copy = revs.pending;
-       revs.leak_pending = 1;
-
-       /*
-        * bisect_common calls prepare_revision_walk right away, which
-        * (together with .leak_pending = 1) makes us the sole owner of
-        * the list of pending objects.
-        */
-       bisect_common(&revs);
+       bisect_common(&revs, &pending_copy);
        res = (revs.commits != NULL);
 
        /* Clean up objects used, as they will be reused. */
@@ -964,7 +957,7 @@ int bisect_next_all(const char *prefix, int no_checkout)
        bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
        revs.limited = 1;
 
-       bisect_common(&revs);
+       bisect_common(&revs, NULL);
 
        find_bisection(&revs.commits, &reaches, &all, !!skipped_revs.nr);
        revs.commits = managed_skipped(revs.commits, &tried);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index e1e157d205..1f04f5d5e5 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -796,14 +796,7 @@ static void orphaned_commit_warning(struct commit *old, 
struct commit *new)
        add_pending_oid(&revs, "HEAD", &new->object.oid, UNINTERESTING);
 
        /* Save pending objects, so they can be cleaned up later. */
-       refs = revs.pending;
-       revs.leak_pending = 1;
-
-       /*
-        * prepare_revision_walk (together with .leak_pending = 1) makes us
-        * the sole owner of the list of pending objects.
-        */
-       if (prepare_revision_walk(&revs))
+       if (prepare_revision_walk_extended(&revs, &refs))
                die(_("internal error in revision walk"));
        if (!(old->object.flags & UNINTERESTING))
                suggest_reattach(old, &revs);
diff --git a/bundle.c b/bundle.c
index 93290962c9..6af6e38c40 100644
--- a/bundle.c
+++ b/bundle.c
@@ -158,14 +158,7 @@ int verify_bundle(struct bundle_header *header, int 
verbose)
        setup_revisions(2, argv, &revs, NULL);
 
        /* Save pending objects, so they can be cleaned up later. */
-       refs = revs.pending;
-       revs.leak_pending = 1;
-
-       /*
-        * prepare_revision_walk (together with .leak_pending = 1) makes us
-        * the sole owner of the list of pending objects.
-        */
-       if (prepare_revision_walk(&revs))
+       if (prepare_revision_walk_extended(&revs, &refs))
                die(_("revision walk setup failed"));
 
        i = req_nr;
diff --git a/revision.c b/revision.c
index f6a3da5cd9..3a231451a4 100644
--- a/revision.c
+++ b/revision.c
@@ -2841,6 +2841,12 @@ void reset_revision_walk(void)
 }
 
 int prepare_revision_walk(struct rev_info *revs)
+{
+       return prepare_revision_walk_extended(revs, NULL);
+}
+
+int prepare_revision_walk_extended(struct rev_info *revs,
+                                  struct object_array *old_pending_ptr)
 {
        int i;
        struct object_array old_pending;
@@ -2860,7 +2866,9 @@ int prepare_revision_walk(struct rev_info *revs)
                        }
                }
        }
-       if (!revs->leak_pending)
+       if (old_pending_ptr)
+               *old_pending_ptr = old_pending;
+       else
                object_array_clear(&old_pending);
 
        /* Signal whether we need per-parent treesame decoration */
diff --git a/revision.h b/revision.h
index 54761200ad..5d4b475334 100644
--- a/revision.h
+++ b/revision.h
@@ -150,18 +150,6 @@ struct rev_info {
                        date_mode_explicit:1,
                        preserve_subject:1;
        unsigned int    disable_stdin:1;
-       /*
-        * Set `leak_pending` to prevent `prepare_revision_walk()` from clearing
-        * the array of pending objects (`pending`). It will still forget about
-        * the array and its entries, so they really are leaked. This can be
-        * useful if the `struct object_array` `pending` is copied before
-        * calling `prepare_revision_walk()`. By setting `leak_pending`, you
-        * effectively claim ownership of the old array, so you should most
-        * likely call `object_array_clear(&pending_copy)` once you are done.
-        * Observe that this is about ownership of the array and its entries,
-        * not the commits referenced by those entries.
-        */
-       unsigned int    leak_pending:1;
        /* --show-linear-break */
        unsigned int    track_linear:1,
                        track_first_time:1,
@@ -270,6 +258,8 @@ extern int handle_revision_arg(const char *arg, struct 
rev_info *revs,
 
 extern void reset_revision_walk(void);
 extern int prepare_revision_walk(struct rev_info *revs);
+extern int prepare_revision_walk_extended(struct rev_info *revs,
+                                         struct object_array *old_pending_ptr);
 extern struct commit *get_revision(struct rev_info *revs);
 extern char *get_revision_mark(const struct rev_info *revs,
                               const struct commit *commit);
-- 
2.15.1

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