LTspice import: don't try loading .asc files for non-subsheets.

Subsheets don't have "Prefix" attribute, components do.

eeschema/sch_plugins/ltspice/ltspice_schematic.cpp

@@ -75,6 +75,16 @@ void LTSPICE_SCHEMATIC::Load( SCHEMATIC* aSchematic, SCH_SHEET* aRootSheet,
                         } );
 
         for( LTSPICE_FILE& newSubSchematicElement : newSubSchematicElements )
+        {
+            wxString asyName = newSubSchematicElement.ElementName;
+            auto     it = mapOfAsyFiles.find( asyName );
+
+            if( it == mapOfAsyFiles.end() )
+                continue;
+
+            wxString asyBuffer = SafeReadFile( it->second, "r" );
+
+            if( IsAsySubsheet( asyBuffer ) )
             {
                 newSubSchematicElement.ParentIndex = parentSheetIndex;
                 newSubSchematicElement.Screen = screen;
@@ -83,6 +93,7 @@ void LTSPICE_SCHEMATIC::Load( SCHEMATIC* aSchematic, SCH_SHEET* aRootSheet,
                 ascFileQueue.push( newSubSchematicElement.ElementName );
                 ascFiles.push_back( newSubSchematicElement );
             }
+        }
 
         ascFileQueue.pop();
 
@@ -264,6 +275,25 @@ std::vector<LTSPICE_FILE> LTSPICE_SCHEMATIC::GetSchematicElements( const wxStrin
 }
 
 
+bool LTSPICE_SCHEMATIC::IsAsySubsheet( const wxString& aAsyFile )
+{
+    wxStringTokenizer lines( aAsyFile, "\n" );
+
+    while( lines.HasMoreTokens() )
+    {
+        wxStringTokenizer parts( lines.GetNextToken(), " " );
+
+        if( parts.GetNextToken().IsSameAs( wxS( "SYMATTR" ), false )
+            && parts.GetNextToken().IsSameAs( wxS( "Prefix" ), false ) )
+        {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
 int LTSPICE_SCHEMATIC::integerCheck( const wxString& aToken, int aLineNumber,
                                      const wxString& aFileName )
 {

eeschema/sch_plugins/ltspice/ltspice_schematic.h

@@ -314,6 +314,13 @@ public:
      */
     std::vector<LTSPICE_FILE> GetSchematicElements( const wxString& aAscFile );
 
+    /**
+     * Check if the asy file content indicates that we need to load subsheet.
+     *
+     * @param aAsyFile contents of .asy file.
+     */
+    bool IsAsySubsheet( const wxString& aAsyFile );
+
     /**
      * The function returns a map. This map has all the asy files in form of string. For asy files
      * the key will be symbol name.