[mypyc] Support isinstance with librt.vecs.vec objects (python#20699)

Use a common base class 'vec' for isinstance support. The base class is
currently only used for isinstance, but we could add some other common
functionality there in the future.

I used some coding agent assist.

Author: JukkaL

mypyc/lib-rt/vecs/librt_vecs.c

@@ -241,10 +241,8 @@ PyTypeObject VecGenericAliasType = {
 // The 'vec' type
 //
 // This cannot be instantiated, and it's only used for isinstance and indexing: vec[T].
-
-typedef struct {
-    PyObject_HEAD
-} Vec;
+// All specialized vec types (VecI64Type, VecI32Type, etc.) inherit from this base type,
+// so isinstance(v, vec) returns True for any specialized vec instance.
 
 static PyObject *extract_optional_item(PyObject *item) {
     PyObject *args = PyObject_GetAttrString(item, "__args__");
@@ -374,9 +372,9 @@ static PyMethodDef vec_methods[] = {
 PyTypeObject VecType = {
     PyVarObject_HEAD_INIT(NULL, 0)
     .tp_name = "vec",
-    .tp_basicsize = sizeof(Vec),
+    .tp_basicsize = sizeof(VecBaseObject),
     .tp_itemsize = 0,
-    .tp_flags = Py_TPFLAGS_DEFAULT,
+    .tp_flags = Py_TPFLAGS_DEFAULT,  // No Py_TPFLAGS_BASETYPE - prevent Python subclassing
     .tp_methods = vec_methods,
 };
 

mypyc/lib-rt/vecs/librt_vecs.h

@@ -157,6 +157,13 @@ typedef struct _VecObject {
     Py_ssize_t len;
 } VecObject;
 
+// Base vec type object (for isinstance checks)
+// This is an abstract base type that all specialized vec types inherit from.
+// It cannot be instantiated directly - only used for isinstance(x, vec).
+typedef struct _VecBaseObject {
+    PyObject_HEAD
+} VecBaseObject;
+
 // Boxed vec[i64]
 typedef struct _VecI64Object {
     PyObject_HEAD

mypyc/lib-rt/vecs/vec_nested.c

@@ -9,6 +9,7 @@
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "librt_vecs.h"
+#include "vecs_internal.h"
 
 static inline VecNested vec_error() {
     VecNested v = { .len = -1 };
@@ -439,6 +440,7 @@ PyTypeObject VecNestedType = {
     .tp_doc = "Mutable sequence-like container optimized for compilation with mypyc",
     .tp_basicsize = sizeof(VecNestedObject),
     .tp_itemsize = 0,
+    .tp_base = &VecType,  // Inherit from base vec type for isinstance() support
     .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
     .tp_traverse = (traverseproc)VecNested_traverse,
     .tp_clear = (inquiry)VecNested_clear,

mypyc/lib-rt/vecs/vec_t.c

@@ -11,6 +11,7 @@
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "librt_vecs.h"
+#include "vecs_internal.h"
 
 static inline VecT vec_error() {
     VecT v = { .len = -1 };
@@ -433,6 +434,7 @@ PyTypeObject VecTType = {
     .tp_doc = "Mutable sequence-like container optimized for compilation with mypyc",
     .tp_basicsize = sizeof(VecTObject),
     .tp_itemsize = 0,
+    .tp_base = &VecType,  // Inherit from base vec type for isinstance() support
     .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
     .tp_traverse = (traverseproc)VecT_traverse,
     .tp_clear = (inquiry)VecT_clear,

mypyc/lib-rt/vecs/vec_template.c

@@ -28,6 +28,7 @@
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "librt_vecs.h"
+#include "vecs_internal.h"
 
 inline static VEC vec_error() {
     VEC v = { .len = -1 };
@@ -370,6 +371,7 @@ PyTypeObject VEC_TYPE = {
     .tp_doc = "Mutable sequence-like container optimized for compilation with mypyc",
     .tp_basicsize = sizeof(VEC_OBJECT),
     .tp_itemsize = 0,
+    .tp_base = &VecType,  // Inherit from base vec type for isinstance() support
     .tp_flags = Py_TPFLAGS_DEFAULT,
     .tp_new = vec_new,
     //.tp_free = PyObject_Del,

mypyc/lib-rt/vecs/vecs_internal.h

@@ -0,0 +1,11 @@
+#ifndef VECS_INTERNAL_H_INCL
+#define VECS_INTERNAL_H_INCL
+
+// Internal header for mypyc/lib-rt/vecs implementation
+
+#include <Python.h>
+
+// The base vec type
+extern PyTypeObject VecType;
+
+#endif  // VECS_INTERNAL_H_INCL

mypyc/test-data/run-vecs-misc-interp.test

@@ -69,6 +69,14 @@ def test_construct_empty() -> None:
         assert type(v) is vec[t]
         assert len(v) == 0
 
+def test_isinstance() -> None:
+    for t in ITEM_TYPES:
+        v = vec[t]()
+        assert isinstance(v, vec)
+        assert not isinstance(vec[t], vec)
+    assert not isinstance("x", vec)
+    assert not isinstance(vec, vec)
+
 def test_basic_int_operations() -> None:
     # All of the non-bool item types support int values 0 to 255
     for t in ITEM_TYPES:

mypyc/test-data/run-vecs-nested-interp.test

@@ -62,6 +62,10 @@ def test_construct_from_initializer_nested() -> None:
     with assertRaises(TypeError):
         vec[str]([vec[bytes]()])
 
+def test_isinstance() -> None:
+    assert isinstance(vec[vec[str]](), vec)
+    assert isinstance(vec[vec[Optional[str]]](), vec)
+
 def test_repr() -> None:
     assert str(vec[vec[str]]()) == "vec[vec[str]]([])"
     assert str(vec[vec[Optional[str]]]()) == "vec[vec[str | None]]([])"

mypyc/test-data/run-vecs-t-interp.test

@@ -100,6 +100,10 @@ def test_construct_from_initializer_optional() -> None:
     with assertRaises(TypeError):
         vec[Optional[str]]([1])
 
+def test_isinstance() -> None:
+    assert isinstance(vec[str](), vec)
+    assert isinstance(vec[Optional[str]](), vec)
+
 def test_append() -> None:
     v = vec[str]()
     v = append(v, '1')