Compare entity instances in one file by identity again

entity_instance.file is a property backed by a fresh SWIG wrapper on every
access, and ifcopenshell::file had no __eq__, so `self.file != other.file`
in entity_instance.__eq__ compared two throwaway wrappers and was always
true - even for an instance against itself. Every entity comparison
therefore took the deep get_info() branch, making distinct but structurally
identical instances compare equal and leaving the final `return False`
unreachable. Bonsai's TestAddRepresentationItemToShapeAspect showed this as
two separate IfcShapeAspects being treated as one, so the stale aspect was
never removed.

Restore the file_pointer() pair that was commented out on both
ifcopenshell::file and express::Base - IfcParseWrapper.i already described
it as the way to "trace file ownership of instances on the python side" -
and give file the __eq__/__hash__ it was missing. The express::Base one
needs $self->file() now that file_ lives on instance_data. This also
repairs rocksdb_lazy_instance.__eq__, which already called file_pointer().

EXPRESS `=` is value comparison and `:=:` is instance comparison, but
rule_compiler emits `==` for both (see the @todo on process_rel_op), and
derived attributes build their operands in the shared global file, so rules
compare same-file instances and need value semantics. Restore those for the
duration of rule execution with settings.compare_instances_by_value,
alongside the existing unpack_non_aggregate_inverses.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/ifcopenshell-python/ifcopenshell/entity_instance.py

@@ -218,7 +218,11 @@ class entity_instance_mixin:
         if self.is_a(True) != other.is_a(True):
             return False
 
-        if self.file != other.file or not self.is_entity():
+        if (
+            settings.compare_instances_by_value
+            or self.file_pointer() != other.file_pointer()
+            or not self.is_entity()
+        ):
             return self.get_info(recursive=True, include_identifier=False) == other.get_info(
                 recursive=True, include_identifier=False
             )

src/ifcopenshell-python/ifcopenshell/express/rule_executor.py

@@ -90,6 +90,12 @@ def run(f: ifcopenshell.file, logger: Logger) -> None:
     orig = ifcopenshell.settings.unpack_non_aggregate_inverses
     ifcopenshell.settings.unpack_non_aggregate_inverses = True
 
+    # Rules are transpiled with EXPRESS `=` emitted as Python `==`, so `==` has
+    # to mean value comparison for the duration. See the @todo on
+    # rule_compiler.process_rel_op.
+    orig_compare = ifcopenshell.settings.compare_instances_by_value
+    ifcopenshell.settings.compare_instances_by_value = True
+
     fn = os.path.join(os.path.dirname(__file__), "rules", f"{f.schema_identifier}.py")
     try:
         source = open(fn, "r").read()
@@ -272,6 +278,7 @@ def run(f: ifcopenshell.file, logger: Logger) -> None:
                 )
 
     ifcopenshell.settings.unpack_non_aggregate_inverses = orig
+    ifcopenshell.settings.compare_instances_by_value = orig_compare
 
 
 if __name__ == "__main__":

src/ifcopenshell-python/ifcopenshell/ifcopenshell_wrapper.pyi

@@ -750,6 +750,7 @@ class entity_instance(entity_instance_mixin):
     def declaration(self) -> declaration: ...
     @property
     def file(self) -> ifcopenshell.file: ...
+    def file_pointer(self) -> int: ...
     def get_argument(self, *args: int | str) -> Any: ...
     def get_argument_index(self, a: str) -> int: ...
     def attribute_name(self, i: int) -> str: ...
@@ -836,6 +837,7 @@ class face:
     def print_impl(self, o, indent): ...
 
 class file(file_mixin):
+    def file_pointer(self) -> int: ...
     def fresh_id(self) -> int: ...
     def __init__(
         self,

src/ifcopenshell-python/ifcopenshell/settings.py

@@ -34,3 +34,24 @@ element or None. Example:
 """
 
 unpack_non_aggregate_inverses = False
+
+"""
+When true compare entity instances by value rather than by identity, even
+when they belong to the same file. EXPRESS uses `=` for value comparison and
+`:=:` for instance comparison, whereas the Python API only has `==`, which
+normally means "the same instance". Example:
+
+>>> import ifcopenshell
+>>> f = ifcopenshell.file(schema='ifc2x3')
+>>> f.createIfcCartesianPoint((0., 0.))
+#1=IfcCartesianPoint((0.,0.))
+>>> f.createIfcCartesianPoint((0., 0.))
+#2=IfcCartesianPoint((0.,0.))
+>>> f[1] == f[2]
+False
+>>> ifcopenshell.settings.compare_instances_by_value = True
+>>> f[1] == f[2]
+True
+"""
+
+compare_instances_by_value = False

src/ifcopenshell-python/test/test_entity_instance.py

@@ -75,6 +75,20 @@ def test_equality():
     assert f[1] == g[1]
     g[1].Coordinates = (1.0, 0.0)
     assert f[1] != g[1]
+    f.createIfcCartesianPoint((0.0, 0.0))
+    assert f[1] == f[1]
+    assert f[1] != f[2]
+
+
+def test_equality_of_owning_file():
+    f = ifcopenshell.file()
+    g = ifcopenshell.file()
+    f.createIfcCartesianPoint((0.0, 0.0))
+    f.createIfcCartesianPoint((0.0, 0.0))
+    g.createIfcCartesianPoint((0.0, 0.0))
+    assert f[1].file == f[1].file
+    assert f[1].file == f[2].file
+    assert f[1].file != g[1].file
 
 
 def test_setting_logical():