Fix a crash in Eeschema when creating a netlist just after saving the project.

This is more a workaround than a fix.
The crash was due to the fact the library cache is modified on the disk with the saving process.

Fixes: lp:1702707
https://bugs.launchpad.net/kicad/+bug/1702707

eeschema/class_library.h

@@ -146,7 +146,7 @@ public:
 
     /**
      * Function GetLibSource
-     * @return the name of the lib to use to load a part, or an a emty string
+     * @return the name of the lib to use to load a part, or an a empty string
      * Useful to load (in lib editor or lib viewer) a part from a given library
      */
     const wxString& GetLibSource() const
@@ -339,8 +339,18 @@ public:
               SCH_IO_MGR::SCH_FILE_T aPluginType = SCH_IO_MGR::SCH_LEGACY );
     ~PART_LIB();
 
+    /**
+     * @return a magic number that changes if the library has changed
+     */
     int GetModHash() const { return m_mod_hash; }
 
+    /**
+     * Forces a change of the magic number that usually changes
+     * if the library has changed. Usefull to force initializations
+     * only made on library change.
+     */
+    void IncModHash() { ++m_mod_hash; }
+
     SCH_IO_MGR::SCH_FILE_T GetPluginType() const { return m_pluginType; }
 
     void SetPluginType( SCH_IO_MGR::SCH_FILE_T aPluginType );

eeschema/class_sch_screen.h

@@ -587,7 +587,16 @@ public:
     int GetMarkerCount( enum MARKER_BASE::TYPEMARKER aMarkerType,
                         enum MARKER_BASE::MARKER_SEVERITY aSeverity );
 
+    /**
+      * initializes or reinitializes the weak reference
+     * to the LIB_PART for each SCH_COMPONENT found in the full schematic
+     * It must be called from:
+     * - Draw function
+     * - when loading a schematic file
+     * - before creating a netlist (in case a library is modified)
+     */
     void UpdateSymbolLinks();
+
     void TestDanglingEnds();
 
     /**

eeschema/libarch.cpp

@@ -52,7 +52,21 @@ bool SCH_EDIT_FRAME::CreateArchiveLibraryCacheFile( bool aUseCurrentSheetFilenam
     fn.SetName( fn.GetName() + "-cache" );
     fn.SetExt( SchematicLibraryFileExtension );
 
-    return CreateArchiveLibrary( fn.GetFullPath() );
+    bool success = CreateArchiveLibrary( fn.GetFullPath() );
+
+    // Mark the library cache as modified:
+    PART_LIBS* libs = Prj().SchLibs();
+    PART_LIB* libcache = libs->FindLibrary( fn.GetName() );
+
+    if( libcache )
+        libcache->IncModHash();
+
+    // Update the schematic symbol library links.
+    // because the lib cache has changed
+    SCH_SCREENS schematic;
+    schematic.UpdateSymbolLinks();
+
+    return success;
 }
 
 
@@ -65,8 +79,8 @@ bool SCH_EDIT_FRAME::CreateArchiveLibrary( const wxString& aFileName )
     // Create a new empty library to archive components:
     std::unique_ptr<PART_LIB> archLib( new PART_LIB( LIBRARY_TYPE_EESCHEMA, aFileName ) );
 
-    archLib->SetCache();
+    // Save symbols to file only when the library will be fully filled
-    archLib->EnableBuffering();    // To save symbols to file only when the library will be fully filled
+    archLib->EnableBuffering();
 
     /* Examine all screens (not hierarchical sheets) used in the schematic and build a
      * library of unique symbols found in all screens.  Complex hierarchies are not a