Reviving #659, closed 2026-09-10 purely to clear a review backlog
(#630), not on merit. Rebuilt fresh against current master rather than
merged from the old branch (elementspanelwidget.cpp had drifted enough
that a textual merge risked silently losing content, as it did earlier
in this same session for a different revival). Builds discussion #607.
Cutting/copying a linked group of elements -- a relay coil with its
contacts, a PLC master with its slave I/O elements -- dropped the
master/slave link entirely. Traced end to end: Element::toXml() writes
each partner's uuid into <link_uuid>, Element::fromXml() reads it back
into a deferred, unresolved buffer (tmp_uuids_link), and the only code
that ever resolves that buffer is initLink(QETProject *) -- called
only from Diagram::refreshContents(), itself only called from full
project load and macro-block insertion. Neither DiagramView::paste()
nor ElementsPanelWidget::duplicateDiagram() ever call it, so
tmp_uuids_link is populated correctly and never resolved: the link is
silently dropped. duplicateDiagram() already knew this and worked
around it by calling clearPendingLinks() -- correct to not link back
to a stale source, but it meant folio duplication never preserved a
link either.
Added Element::initLink(const QList<Element *> &candidates) --
resolves against a caller-supplied list instead of a project-wide
search. The scoping is the subtle part: right after the XML round-trip
and before uuids are renewed, a pasted/duplicated element's
tmp_uuids_link still holds its source's original partner uuid, which
at that exact moment still equals the not-yet-renewed uuid of that
partner's own copy, if it was carried along in the same batch.
Resolving only within the batch is what stops a linked pair pasted
together from matching an original element left elsewhere that
happens to still carry that same soon-to-be-replaced uuid. If only one
half of a linked group is in the batch, its entry finds no match and
is dropped -- the same "leave it unlinked" outcome as before.
Wired into PasteDiagramCommand::redo(), before the existing newUuid()
loop and gated by the same first_redo flag. Wired into
duplicateDiagram() the same way, replacing its clearPendingLinks()
call (initLink() clears tmp_uuids_link internally, matched or not).
Verified live -- the original PR's own test plan left both of these
unchecked, so this closes that gap rather than repeating it. Built a
project with a linked PLC master/slave pair (qet-mcp's link_elements),
then drove the real interaction under Xvfb:
Ctrl+A, Ctrl+C, Ctrl+V:
originals 95ad58fc <-> e728632c (unchanged)
pasted 513e6bf8 <-> 29aa60b4 (linked to each other)
Right-click folio > "Copier et coller":
originals 95ad58fc <-> e728632c (unchanged)
duplicated 0a33ccb4 <-> 3264fe66 (linked to each other)
Neither copy links back to an original or comes in unlinked. Qt 6.10.2,
ctest 13/13.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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