[MLIR][Python] make Sliceable inherit from Sequence (#170551)

Generates type stubs like

```python
class RegionSequence(Sequence[Region]):
    def __add__(self, arg: RegionSequence, /) -> list[Region]: ...

    def __iter__(self) -> RegionIterator:
        """Returns an iterator over the regions in the sequence."""
```

Author: makslevental

mlir/lib/Bindings/Python/NanobindUtils.h

@@ -19,6 +19,7 @@
 #include "llvm/Support/raw_ostream.h"
 
 #include <string>
+#include <typeinfo>
 #include <variant>
 
 template <>
@@ -344,7 +345,16 @@ class Sliceable {
 
   /// Binds the indexing and length methods in the Python class.
   static void bind(nanobind::module_ &m) {
-    auto clazz = nanobind::class_<Derived>(m, Derived::pyClassName)
+    const std::type_info &elemTy = typeid(ElementTy);
+    PyObject *elemTyInfo = nanobind::detail::nb_type_lookup(&elemTy);
+    assert(elemTyInfo &&
+           "expected nb_type_lookup to succeed for Sliceable elemTy");
+    nanobind::handle elemTyName = nanobind::detail::nb_type_name(elemTyInfo);
+    std::string sig = std::string("class ") + Derived::pyClassName +
+                      "(collections.abc.Sequence[" +
+                      nanobind::cast<std::string>(elemTyName) + "])";
+    auto clazz = nanobind::class_<Derived>(m, Derived::pyClassName,
+                                           nanobind::sig(sig.c_str()))
                      .def("__add__", &Sliceable::dunderAdd);
     Derived::bindDerived(clazz);
 

mlir/test/python/ir/operation.py

@@ -43,6 +43,10 @@ def testTraverseOpRegionBlockIterators():
     )
     op = module.operation
     assert op.context is ctx
+    # Note, __nb_signature__ stores the fully-qualified signature - the actual type stub emitted is
+    # class RegionSequence(Sequence[Region])
+    # CHECK: class RegionSequence(collections.abc.Sequence[mlir._mlir_libs._mlir.ir.Region])
+    print(RegionSequence.__nb_signature__)
     # Get the block using iterators off of the named collections.
     regions = list(op.regions[:])
     blocks = list(regions[0].blocks)