use set_rejected_and_compute_diff_provides for package removal

Patch by Anssi Hannula, fixes bug #52667

k1-1 provides k, but not k1-2
l-1 and l-2 requires k
m-1 requires k but not m-2
n requires m

User has l-1, m-1, n-1, k1-1.

There is only one upgrade path:
k1-1 -> k1-2
m-1 -> m-2
removal of l-1

When transaction is created with all of them (e.g. what --auto-select does
first), the path is resolved correctly.
However, when the upgrade is triggered with the upgrade of k1, and l is in RPM
db before n, resolving proceeds as follows:
1. k1 selected and old version rejected
2. l is promoted
3. m is promoted
4. l-2 is therefore selected
5. no packages are found for k (as k1-1 was rejected in step 1)
6. backtrack_selected calls resolve_rejected to reject the chain
7. rejection process rejects l, m, n
8. m-2 is selected because of step 3
End result: n is wrongly removed.

Therefore, when using --auto-select (with --split-length 1 --split-level 1 in
this small case, to force splitting) to trigger the upgrade, the early resolve
is done correctly, but the first splitted transaction ("rpms sorted by
dependencies" has k1 and m separately, so split is tried) tries to remove n and
URPM fallbacks to single big transaction.

In reverse, when using "urpmi k1" to trigger the upgrade, urpmi asks user
confirmation for n removal, but the transaction is created with both k1 and m
("rpms sorted by dependencies" has k1+m, so they are put in same transaction),
thus triggering the correct behaviour and n is not really removed after all,
even if user agreed to it.

Attached patch fixes this by switching backtrack_selected() to use
set_rejected_and_compute_diff_provides() for package removal instead of
resolve_rejected_(). The code already contained a comment indicating that
diff_provides code should be applied.
The patch introduces no regression in the urpmi and perl-URPM testsuites.

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 50a827b..2bafaa6 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,5 @@
+- backtrack_selected: use set_rejected_and_compute_diff_provides for package
+  removal (Anssi Hannula)
 - obey options (keep, nodeps) when unselecting current package in the case
   that was added in 3.31 (Anssi Hannula)