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Reject non-finite element/terminal coordinates on load (fixes #781, #782)

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QString::toDouble() reports a successful conversion for "nan"/"inf"/
"-inf" -- confirmed directly -- so the existing conv_ok checks in
Element::valideXml() and Terminal::valideXml() never caught a
non-finite x/y. A NaN-positioned element reaching the scene can hang
QGraphicsScene::addItem() forever: an existing conductor's itemChange()
runs a collision test (calculateTextItemPosition() ->
QGraphicsItem::collidesWithPath()) whose underlying QPathClipper spins
without terminating when fed a NaN-valued QPainterPath, since NaN
breaks the ordering comparisons the clipping algorithm's termination
depends on (#781). Short of that, a non-finite value that doesn't
happen to trigger a collision test simply gets written straight back
out on save with nothing to stop it (#782).

Element::valideXml() and Terminal::valideXml() now also check
qIsFinite() on the parsed x/y, rejecting the whole item the same way a
missing attribute already does. DynamicElementTextItem::fromXml() has
no such reject-the-item gate (void return, no caller check), so its x/y
are clamped to 0 instead -- the same fallback the attribute lookup
already uses when x/y is missing entirely.

Verified against both original findings' exact repro steps:
- #781: Habitat-Unifilaire.qet with x="nan" on one element -- hung
  (SIGTERM'd by a 25s timeout) on an unfixed build, resaves cleanly
  (exit 0) on this one.
- #782: grafcet.qet with y="nan" on a dynamic_elmt_text -- the value
  passed straight through to the resaved file on an unfixed build;
  clamped to 0 on this one. The specific field is now stable (y="0" on
  two consecutive resaves) where it read "nan" both times before.
  (grafcet.qet has an unrelated, already-known, unmerged fix
  (PR #779) for element/terminal-order non-determinism, so a whole-file
  diff across resaves still differs for reasons unconnected to this
  change -- checked the specific once-NaN field in isolation instead.)
- Also checked -inf on affuteuse_250h.qet: same rejection, same result.

Full qet-dbcheck.py sweep of the unmutated example corpus (23
projects), 0 regressions.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
ispyisail
2026-08-25 13:23:05 +12:00
parent 26d7c03a76
commit 68e507a522
3 changed files with 30 additions and 10 deletions
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sources/qetgraphicsitem/element.cpp
+10 -4
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@@ -53,6 +53,7 @@ static const QString plcTerminalKeys[] = {
#include <QDebug>
#include <QDomElement>
#include <QtCore/qnumeric.h>
#include <utility>
class ElementXmlRetroCompatibility
@@ -699,11 +700,16 @@ bool Element::valideXml(QDomElement &e)
}
bool conv_ok;
e.attribute(QStringLiteral("x")).toDouble(&conv_ok);
if (!conv_ok) return(false);
//QString::toDouble() accepts "nan"/"inf"/"-inf" and reports a
//successful conversion for them, so conv_ok alone doesn't reject a
//non-finite coordinate. A NaN position reaching the scene can hang
//QGraphicsScene::addItem() forever inside Qt's own polygon-clipping
//code when an existing conductor's collision test runs against it.
double x = e.attribute(QStringLiteral("x")).toDouble(&conv_ok);
if (!conv_ok || !qIsFinite(x)) return(false);
e.attribute(QStringLiteral("y")).toDouble(&conv_ok);
if (!conv_ok) return(false);
double y = e.attribute(QStringLiteral("y")).toDouble(&conv_ok);
if (!conv_ok || !qIsFinite(y)) return(false);
return(true);
}