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Preserve master/slave links when pasting or duplicating a folio

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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>
This commit is contained in:
ispyisail
2026-09-23 16:37:45 +12:00
parent 6d8459d647
commit de9b3eae06
4 changed files with 87 additions and 4 deletions
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sources/elementspanelwidget.cpp
+24 -3
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@@ -674,6 +674,27 @@ void ElementsPanelWidget::duplicateDiagram()
bool erase_labels = settings.value(
"diagramcommands/erase-label-on-copy", true).toBool();
// Resolve a linked pair duplicated together against each other
// (bugtracker #607) before the loop below renews their uuids or
// clears their pending links: at this exact moment a copy's
// tmp_uuids_link still holds its source's original partner
// uuid, which still equals the not-yet-renewed uuid of that
// partner's own copy if both were duplicated together. Scoped
// to this diagram's own copies, not a project-wide search, so
// this never links back to the source elements the copies were
// made from -- if only one half of a linked pair is here, its
// link entry simply finds no match and is dropped, same as
// clearPendingLinks() used to do unconditionally for every copy.
QList<Element *> new_elements;
for (QGraphicsItem *item : new_diagram->items()) {
if (Element *elmt = dynamic_cast<Element *>(item)) {
new_elements << elmt;
}
}
for (Element *elmt : new_elements) {
elmt->initLink(new_elements);
}
for (QGraphicsItem *item : new_diagram->items()) {
if (Element *elmt = dynamic_cast<Element *>(item)) {
// The XML round-trip kept the source elements' uuids. Give the
@@ -695,9 +716,9 @@ void ElementsPanelWidget::duplicateDiagram()
new_diagram->restoreText(elmt);
}
// Clear pending links so copies don't link back to
// the source elements via stale UUIDs.
elmt->clearPendingLinks();
// initLink() above already cleared tmp_uuids_link for
// every copy, matched or not -- nothing left here that
// could link back to a stale source uuid.
// Clean up copied element data:
// 1. Slaves always lose label/formula/comment/location