--feedback on migrate:rollback prints the import message with zero counts (regression in 6.1.4)

Problem/Motivation

With drush migrate:rollback --feedback=N, every Nth deleted row prints the import progress message instead of a rollback message:

[notice] Processed 0 items (0 created, 0 updated, 0 failed, 0 ignored) - continuing with 'my_migration'

The counters are then reset, so the closing Rolled back X items - done with '…' line only counts the rows since the last feedback point. A rollback of 975 rows with --feedback=500 prints Processed 0 items … followed by Rolled back 475 items - done, and the first 500 rows are not reported anywhere.

MigrateExecutable::onPostRowDelete() calls progressMessageEmit(FALSE), which reads the save counters. Nothing is saved during a rollback, so those counters are always zero there. rollbackMessage($done) already has a continuing with variant for this case.

The call was changed from rollbackMessage(FALSE) to progressMessageEmit(FALSE) in #3067165 (commit bf849bf5, first released in 6.1.4). The change is listed in comment #45's MR 7 → MR 19 comparison, but the thread does not give a reason for it. onPostRowDelete() only runs during a rollback, and MigrateBatchExecutable, which the progressMessage()/progressMessageEmit() split was made for, has no rollback path. 6.0.x and 6.1.0–6.1.3 print Rolled back N items - continuing with '…'.

#3590774 reverted another side effect of the same commit.

Steps to reproduce

1. Enable migrate_tools_test.
2. drush migrate:import fruit_terms (3 rows)
3. drush migrate:rollback fruit_terms --feedback=2

Actual:

[notice] Processed 0 items (0 created, 0 updated, 0 failed, 0 ignored) - continuing with 'fruit_terms'
[notice] Rolled back 1 item - done with 'fruit_terms'

Expected (6.1.3 behaviour):

[notice] Rolled back 2 items - continuing with 'fruit_terms'
[notice] Rolled back 1 item - done with 'fruit_terms'

Proposed resolution

Restore the rollbackMessage(FALSE) call in MigrateExecutable::onPostRowDelete(), and add a functional test (DrushCommandsTest::testRollbackFeedback()) next to the existing import testFeedback().

Remaining tasks

• Review the MR.

User interface changes

None.

API changes

None.

Data model changes

None.