Eeschema: fix copy and paste bug.

Add required library symbols to new file formatter and parser when copying
schematic symbols to prevent missing library symbol when pasting into a
different schematic which may not have the same library symbol available.

Fix a minor bug where the default schematic symbol reference was not set
by the parser when loading.

Fixes https://gitlab.com/kicad/code/kicad/issues/4442

eeschema/sch_sexpr_parser.cpp

@@ -1937,9 +1937,6 @@ void SCH_SEXPR_PARSER::ParseSchematic( SCH_SHEET* aSheet, bool aIsCopyableOnly,
 
         case T_lib_symbols:
         {
-            if( aIsCopyableOnly )
-                Unexpected( T_lib_symbols );
-
             // Dummy map.  No derived symbols are allowed in the library cache.
             LIB_PART_MAP symbolLibMap;
 
@@ -2032,7 +2029,6 @@ void SCH_SEXPR_PARSER::ParseSchematic( SCH_SHEET* aSheet, bool aIsCopyableOnly,
         }
     }
 
-    if( !aIsCopyableOnly )
     screen->UpdateLocalLibSymbolLinks();
 }
 
@@ -2153,6 +2149,33 @@ SCH_COMPONENT* SCH_SEXPR_PARSER::parseSchematicSymbol()
             // the field positions are set.
             field = parseSchField( symbol.get() );
 
+            // Set the default symbol reference prefix.
+            if( field->GetId() == REFERENCE )
+            {
+                wxString refDesignator = field->GetText();
+
+                refDesignator.Replace( "~", " " );
+
+                wxString prefix = refDesignator;
+
+                while( prefix.Length() )
+                {
+                    if( ( prefix.Last() < '0' || prefix.Last() > '9') && prefix.Last() != '?' )
+                        break;
+
+                    prefix.RemoveLast();
+                }
+
+                // Avoid a prefix containing trailing/leading spaces
+                prefix.Trim( true );
+                prefix.Trim( false );
+
+                if( prefix.IsEmpty() )
+                    symbol->SetPrefix( wxString( "U" ) );
+                else
+                    symbol->SetPrefix( prefix );
+            }
+
             if( symbol->GetField( field->GetId() ) )
                 *symbol->GetField( field->GetId() ) = *field;
             else

eeschema/sch_sexpr_plugin.cpp

@@ -77,7 +77,7 @@
 #include <sch_sexpr_parser.h>
 #include <symbol_lib_table.h>  // for PropPowerSymsOnly definintion.
 #include <confirm.h>
-#include <tool/selection.h>
+#include <ee_selection.h>
 #include <default_values.h>    // For some default values
 
 
@@ -771,13 +771,54 @@ void SCH_SEXPR_PLUGIN::Format( SCH_SHEET* aSheet )
 }
 
 
-void SCH_SEXPR_PLUGIN::Format( SELECTION* aSelection, OUTPUTFORMATTER* aFormatter )
+void SCH_SEXPR_PLUGIN::Format( EE_SELECTION* aSelection, OUTPUTFORMATTER* aFormatter )
 {
+    wxCHECK( aSelection && aFormatter, /* void */ );
+
     m_out = aFormatter;
 
-    for( unsigned i = 0; i < aSelection->GetSize(); ++i )
+    size_t i;
+    SCH_ITEM* item;
+    std::map<wxString, LIB_PART*> libSymbols;
+    SCH_SCREEN* screen = aSelection->GetScreen();
+
+    for( i = 0; i < aSelection->GetSize(); ++i )
     {
-        SCH_ITEM* item = (SCH_ITEM*) aSelection->GetItem( i );
+        item = dynamic_cast<SCH_ITEM*>( aSelection->GetItem( i ) );
+
+        wxCHECK2( item, continue );
+
+        if( item->Type() != SCH_COMPONENT_T )
+            continue;
+
+        SCH_COMPONENT* symbol = dynamic_cast<SCH_COMPONENT*>( item );
+
+        wxCHECK2( symbol, continue );
+
+        wxString libSymbolLookup = symbol->GetLibId().Format().wx_str();
+
+        if( !symbol->UseLibIdLookup() )
+            libSymbolLookup = symbol->GetSchSymbolLibraryName();
+
+        auto it = screen->GetLibSymbols().find( libSymbolLookup );
+
+        if( it != screen->GetLibSymbols().end() )
+            libSymbols[ libSymbolLookup ] = it->second;
+    }
+
+    if( !libSymbols.empty() )
+    {
+        m_out->Print( 0, "(lib_symbols\n" );
+
+        for( auto libSymbol : libSymbols )
+            SCH_SEXPR_PLUGIN_CACHE::SaveSymbol( libSymbol.second, *m_out, 1, libSymbol.first );
+
+        m_out->Print( 0, ")\n\n" );
+    }
+
+    for( i = 0; i < aSelection->GetSize(); ++i )
+    {
+        item = (SCH_ITEM*) aSelection->GetItem( i );
 
         switch( item->Type() )
         {

eeschema/sch_sexpr_plugin.h

@@ -41,7 +41,7 @@ class SCH_TEXT;
 class SCH_COMPONENT;
 class SCH_FIELD;
 class PROPERTIES;
-class SELECTION;
+class EE_SELECTION;
 class SCH_SEXPR_PLUGIN_CACHE;
 class LIB_PART;
 class PART_LIB;
@@ -96,7 +96,7 @@ public:
 
     void Format( SCH_SHEET* aSheet );
 
-    void Format( SELECTION* aSelection, OUTPUTFORMATTER* aFormatter );
+    void Format( EE_SELECTION* aSelection, OUTPUTFORMATTER* aFormatter );
 
     void EnumerateSymbolLib( wxArrayString&    aSymbolNameList,
                              const wxString&   aLibraryPath,

eeschema/tools/ee_selection.cpp

@@ -25,6 +25,13 @@
 #include <tools/ee_selection.h>
 
 
+EE_SELECTION::EE_SELECTION( SCH_SCREEN* aScreen ) :
+    SELECTION()
+{
+    m_screen = aScreen;
+}
+
+
 EDA_ITEM* EE_SELECTION::GetTopLeftItem( bool onlyModules ) const
 {
     EDA_ITEM* topLeftItem = nullptr;

eeschema/tools/ee_selection.h

@@ -25,13 +25,26 @@
 #ifndef EE_SELECTION_H
 #define EE_SELECTION_H
 
+class SCH_SCREEN;
+
+
 #include <tool/selection.h>
 
 
 class EE_SELECTION : public SELECTION
 {
+    /**
+     * Screen of selected objects.  Used to fetch library symbols for copy.
+     */
+    SCH_SCREEN* m_screen;
+
 public:
+    EE_SELECTION( SCH_SCREEN* aScreen = nullptr );
+
     EDA_ITEM* GetTopLeftItem( bool onlyModules = false ) const override;
+
+    void SetScreen( SCH_SCREEN* aScreen ) { m_screen = aScreen; }
+    SCH_SCREEN* GetScreen() { return m_screen; }
 };
 
 #endif  //  EE_SELECTION_H

eeschema/tools/sch_editor_control.cpp

@@ -1094,6 +1094,7 @@ bool SCH_EDITOR_CONTROL::doCopy()
     if( !selection.GetSize() )
         return false;
 
+    selection.SetScreen( m_frame->GetScreen() );
     m_supplementaryClipboard.clear();
 
     for( EDA_ITEM* item : selection )