KiCad 9 refuses to load any schematic whose lib_symbols section contains
an (extends ...) clause, because the extends mechanism is only valid
inside .kicad_sym library files - not inside schematics.
The previous implementation kept the (extends ...) clause and prepended
the parent symbol block with a qualified name, but left the child's
extends referring to the unqualified parent name, causing:
'Error loading schematic: No parent for extended symbol Q_NMOS_GSD'
Fix: add _iter_top_level_items() and _inline_extends_symbol() helpers.
When a library symbol uses extends, the parent's content (pins, graphics,
sub-symbols) is now merged directly into the child definition:
- Parent properties are overridden by child property values
- Sub-symbol names are renamed from ParentName_X_Y to ChildName_X_Y
- The (extends ...) clause is removed entirely
- Only the fully-resolved child symbol is injected into lib_symbols
Affected symbols include Transistor_FET:2N7002, Transistor_BJT:*,
Regulator_Linear:*, Regulator_Switching:* and many others (~30% of the
KiCad standard library uses extends).
Fixes#52
2340afe9a4