Fix report-link colour/style mismatch detection (bugtracker #974)

LinkElementCommand::redo() already had a check meant to catch exactly
this -- two report-linked conductors whose properties disagree -- and
ask the user which to keep via PotentialSelectorDialog. It never
worked: it built ONE combined list from three unrelated fields
(tension_protocol, wire_color, wire_section) and tested that whole
list for string equality, so a tension-protocol value could never
equal a wire-colour value even when every field individually matched
across every conductor. Worse, "wire_color"/"wire_section" are
ConductorProperties::m_wire_color/m_wire_section, a separate free-text
documentation pair that says nothing about how the wire is actually
drawn -- that's "color"/"style" -- so the one field #974 is actually
about was never compared at all.

Fixed by comparing each relevant field (text/num, function, tension
protocol, colour, line style) separately. Downloaded the reporter's
actual project, confirmed the mismatched wire reads color="#0000ff" on
one side of a "Folio suivant"/"Folio precedent" link and
color="#55aa00" on the other, with the link's other four conductors
matching correctly (ruling out a rendering artifact) -- see PR #980's
checkContinuity() extension, which now flags this class of mismatch on
sight.

Extracted the comparison into its own static
reportLinkNeedsPotentialChoice(), for the same reason
ConductorCreator::needsPotentialChoice() already exists as its own
method: a caller with nobody there to answer a modal dialog needs to
check first and decline, and the condition must not drift away from
the one redo() actually applies.

Fixing the comparison surfaced a real, previously-latent hang in this
session's own qet.linkElements(): PotentialSelectorDialog::exec() is a
plain QDialog::exec(), not routed through QET::QetMessageBox, so
headless --run has nobody to answer it. Measured directly -- hung
until killed with the property-comparison fix alone, clean refusal
after adding the guard. linkElements() now calls
reportLinkNeedsPotentialChoice() before constructing the command and
declines with a clear reason, the same choice addConductor() already
makes about ConductorCreator's own equivalent dialog.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

sources/undocommand/linkelementcommand.cpp

@@ -314,31 +314,15 @@ void LinkElementCommand::redo()
 	if(m_element->diagram()) m_element->diagram()->showMe();
 	makeLink(m_linked_after);
 
-		//If the action is to link two reports together, we check if the conductors
+		//If the action is to link two reports together, and the conductors
-		//of the new potential have the same text, function, and protocol.
+		//of the new potential disagree on a property that matters, a
-		//if not, a dialog ask what do to.
+		//dialog asks what to do. See reportLinkNeedsPotentialChoice() for
+		//what "disagree" checks and the bug fixed there (bugtracker #974).
 	if (m_first_redo && (m_element->linkType() & Element::AllReport) \
 		&& m_element->conductors().size() \
 		&& m_linked_after.size() && m_linked_after.first()->conductors().size())
 	{
-			//fill list of potential
+		if (reportLinkNeedsPotentialChoice(m_element, m_linked_after.first()))
-		QSet <Conductor *> c_list = m_element->conductors().first()->relatedPotentialConductors();
-		c_list << m_element->conductors().first();
-			//fill list of text
-		QStringList str_txt;
-		QStringList str_funct;
-		QStringList str_tens;
-		for (const Conductor *c : c_list)
-		{
-			str_txt   << c->properties().text;
-			str_funct << c->properties().m_function;
-			str_tens  << c->properties().m_tension_protocol;
-			str_tens  << c->properties().m_wire_color;
-			str_tens  << c->properties().m_wire_section;
-		}
-
-			//check text list, isn't same in potential, ask user what to do
-		if (!QET::eachStrIsEqual(str_txt) || !QET::eachStrIsEqual(str_funct) || !QET::eachStrIsEqual(str_tens))
 		{
 			PotentialSelectorDialog psd(m_element, this);
 			psd.exec();
@@ -348,6 +332,64 @@ void LinkElementCommand::redo()
 	QUndoCommand::redo();
 }
 
+/**
+	@brief LinkElementCommand::reportLinkNeedsPotentialChoice
+	Whether linking these two report elements (next_report/previous_report)
+	would pop PotentialSelectorDialog -- i.e. whether their conductors (if
+	any exist yet, on either side) disagree on a property redo() cares
+	about. Exposed as its own static method, rather than left inline in
+	redo(), for the same reason ConductorCreator::needsPotentialChoice()
+	is: a caller with nobody there to answer a modal dialog (the scripting
+	API) can check first and decline, and the condition cannot drift away
+	from the one redo() actually applies.
+
+	Bug fixed here (bugtracker #974): the original check built ONE
+	combined list from three unrelated fields (tension_protocol,
+	wire_color, wire_section) and tested that whole list for equality --
+	comparing a tension-protocol string against a wire-colour string is
+	never equal even when each field individually matches across every
+	conductor, and wire_color/wire_section are ConductorProperties::
+	m_wire_color/m_wire_section, a separate free-text documentation pair
+	that says nothing about how the wire is actually drawn (that is
+	"color"/"style"). Net effect: the dialog could not reliably detect a
+	real mismatch, including the exact case #974 reported -- two
+	report-linked conductors drawn in different colours -- and could just
+	as easily fire on conductors that matched in every way that mattered.
+	Comparing each relevant field (text/num, function, tension protocol,
+	colour, line style) on its own fixes both.
+
+	@param element_a @param element_b the two elements about to be (or
+	already) linked; order does not matter
+	@return true if the dialog would (or does) open
+*/
+bool LinkElementCommand::reportLinkNeedsPotentialChoice(Element *element_a, Element *element_b)
+{
+	if (!element_a || !element_b) return false;
+	if (element_a->conductors().isEmpty() || element_b->conductors().isEmpty()) return false;
+
+	QSet<Conductor *> c_list;
+	for (Element *e : {element_a, element_b})
+	{
+		if (e->conductors().isEmpty()) continue;
+		c_list << e->conductors().first();
+		c_list += e->conductors().first()->relatedPotentialConductors();
+	}
+	if (c_list.size() < 2) return false;
+
+	QStringList str_txt, str_funct, str_tens, str_color, str_style;
+	for (const Conductor *c : std::as_const(c_list))
+	{
+		str_txt   << c->properties().text;
+		str_funct << c->properties().m_function;
+		str_tens  << c->properties().m_tension_protocol;
+		str_color << c->properties().color.name();
+		str_style << QString::number(int(c->properties().style));
+	}
+	return !QET::eachStrIsEqual(str_txt) || !QET::eachStrIsEqual(str_funct)
+		|| !QET::eachStrIsEqual(str_tens) || !QET::eachStrIsEqual(str_color)
+		|| !QET::eachStrIsEqual(str_style);
+}
+
 /**
 	@brief LinkElementCommand::setUpNewLink
 	Update the content of m_link_after with the content of element_list.

sources/undocommand/linkelementcommand.h

@@ -38,6 +38,7 @@ class LinkElementCommand : public QUndoCommand
 		bool mergeWith(const QUndoCommand *other) override;
 
 		static bool isLinkable (Element *element_a, Element *element_b, bool already_linked = false);
+		static bool reportLinkNeedsPotentialChoice(Element *element_a, Element *element_b);
 
 		void setLink (const QList<Element *>& element_list);
 		void setLink (Element *element_);