DIALOG_LABEL_PROPERTIES, add global label: better filtering of candidates.

The list of candidates (names) must be restricted to existing global labels
and symbols creating a global net name: power symbols having only one power
input pin (a power output does not create net name).
Fixes #14319
https://gitlab.com/kicad/code/kicad/issues/14319

eeschema/dialogs/dialog_label_properties.cpp

@@ -286,6 +286,10 @@ bool DIALOG_LABEL_PROPERTIES::TransferDataToWindow()
                 for( SCH_ITEM* item : screen->Items().OfType( SCH_SYMBOL_LOCATE_POWER_T ) )
                 {
                     const SCH_SYMBOL* power = static_cast<const SCH_SYMBOL*>( item );
+
+                    // Ensure the symbol has the Power (i.e. equivalent to a global label
+                    // before adding its value in list
+                    if( power->IsSymbolLikePowerGlobalLabel() )
                         existingLabels.insert( UnescapeString( power->GetValueFieldText( false ) ) );
                 }
             }

eeschema/sch_symbol.cpp

@@ -2329,3 +2329,22 @@ bool SCH_SYMBOL::IsPointClickableAnchor( const VECTOR2I& aPos ) const
 
     return false;
 }
+
+
+bool SCH_SYMBOL::IsSymbolLikePowerGlobalLabel() const
+{
+    // return true if the symbol is equivalent to a global label:
+    // It is a Power symbol
+    // It has only one pin type Power input
+
+    if( !GetLibSymbolRef() || !GetLibSymbolRef()->IsPower() )
+        return false;
+
+    std::vector<LIB_PIN*> pin_list = GetAllLibPins();
+
+    if( pin_list.size() != 1 )
+        return false;
+
+    return pin_list[0]->GetType() == ELECTRICAL_PINTYPE::PT_POWER_IN;
+}
+

eeschema/sch_symbol.h

@@ -756,6 +756,13 @@ public:
 
     bool IsPointClickableAnchor( const VECTOR2I& aPos ) const override;
 
+    /**
+     * @return true if the symbol is equivalent to a global label:
+     * It is a Power symbol
+     * It has only one pin type Power input
+     */
+    bool IsSymbolLikePowerGlobalLabel() const;
+
 private:
     BOX2I doGetBoundingBox( bool aIncludePins, bool aIncludeFields ) const;