Add a simple hash for sch_tables to avoid too much reordering in the saved schematic file

Fixes https://gitlab.com/kicad/code/kicad/-/issues/20918

eeschema/sch_io/kicad_sexpr/sch_io_kicad_sexpr.cpp

@@ -401,6 +401,15 @@ void SCH_IO_KICAD_SEXPR::Format( SCH_SHEET* aSheet )
                 if( a->Type() != b->Type() )
                     return a->Type() < b->Type();
 
+                // sorting fix specific for 9.0 to avoid format change
+                if( a->Type() == SCH_TABLE_T && b->Type() == SCH_TABLE_T )
+                {
+                    const SCH_TABLE* aTable = static_cast<const SCH_TABLE*>( a );
+                    const SCH_TABLE* bTable = static_cast<const SCH_TABLE*>( b );
+
+                    return aTable->GetHash() < bTable->GetHash();
+                }
+
                 return a->m_Uuid < b->m_Uuid;
             };
 

eeschema/sch_table.cpp

@@ -628,6 +628,25 @@ double SCH_TABLE::Similarity( const SCH_ITEM& aOther ) const
 }
 
 
+size_t SCH_TABLE::GetHash() const
+{
+    size_t hash = 0;
+
+    // The goal here is to generate an hash that would change the least for
+    // mundane things like just moving the table.
+
+    hash_combine( hash, m_colCount );
+    hash_combine( hash, m_rowHeights.size() );
+
+    for( SCH_TABLECELL* cell : m_cells )
+    {
+        hash_combine( hash, cell->GetText() );
+    }
+
+    return hash;
+}
+
+
 static struct SCH_TABLE_DESC
 {
     SCH_TABLE_DESC()

eeschema/sch_table.h

@@ -245,6 +245,12 @@ public:
     void Show( int nestLevel, std::ostream& os ) const override { ShowDummy( os ); }
 #endif
 
+    /**
+     * This function exists to keep tables sorted on save in 9.0 as the uuid
+     * is missing.
+     */
+    size_t GetHash() const;
+
 protected:
     bool                        m_strokeExternal;
     bool                        m_StrokeHeaderSeparator;