Add Oid.__bool__ + clarify Oid docs/stubs

docs/oid.rst

@@ -56,9 +56,9 @@ The Oid type
      >>> raw = unhexlify("cff3ceaefc955f0dbe1957017db181bc49913781")
      >>> oid2 = Oid(raw=raw)
 
-And the other way around, from an Oid object we can get the hexadecimal and raw
-forms. You can use the built-in `str()` (or `unicode()` in python 2) to get the
-hexadecimal representation of the Oid.
+And the other way around, from an Oid object we can get the raw form via
+`oid.raw`. You can use `str(oid)` to get the hexadecimal representation of the
+Oid.
 
 .. method:: Oid.__str__()
 .. autoattribute:: pygit2.Oid.raw
@@ -68,8 +68,11 @@ The Oid type supports:
 - rich comparisons, not just for equality, also: lesser-than, lesser-or-equal,
   etc.
 
-- hashing, so Oid objects can be used as keys in a dictionary.
+- `hash(oid)`, so Oid objects can be used as keys in a dictionary.
 
+- `bool(oid)`, returning False if the Oid is a null SHA-1 (all zeros).
+
+- `str(oid)`, returning the hexadecimal representation of the Oid.
 
 Constants
 =========

pygit2/_pygit2.pyi

@@ -262,7 +262,6 @@ class OdbBackendPack(OdbBackend):
     def __init__(self, *args, **kwargs) -> None: ...
 
 class Oid:
-    hex: str
     raw: bytes
     def __init__(self, raw: bytes = ..., hex: str = ...) -> None: ...
     def __eq__(self, other) -> bool: ...
@@ -272,6 +271,7 @@ class Oid:
     def __le__(self, other) -> bool: ...
     def __lt__(self, other) -> bool: ...
     def __ne__(self, other) -> bool: ...
+    def __bool__(self) -> bool: ...
 
 class Patch:
     data: bytes

src/oid.c

@@ -34,6 +34,8 @@
 
 PyTypeObject OidType;
 
+static const git_oid oid_zero = GIT_OID_SHA1_ZERO;
+
 
 PyObject *
 git_oid_to_python(const git_oid *oid)
@@ -255,6 +257,13 @@ Oid__str__(Oid *self)
     return git_oid_to_py_str(&self->oid);
 }
 
+int
+Oid__bool(PyObject *self)
+{
+    git_oid *oid = &((Oid*)self)->oid;
+    return !git_oid_equal(oid, &oid_zero);
+}
+
 PyDoc_STRVAR(Oid_raw__doc__, "Raw oid, a 20 bytes string.");
 
 PyObject *
@@ -269,6 +278,45 @@ PyGetSetDef Oid_getseters[] = {
     {NULL},
 };
 
+PyNumberMethods Oid_as_number = {
+     0,                          /* nb_add */
+     0,                          /* nb_subtract */
+     0,                          /* nb_multiply */
+     0,                          /* nb_remainder */
+     0,                          /* nb_divmod */
+     0,                          /* nb_power */
+     0,                          /* nb_negative */
+     0,                          /* nb_positive */
+     0,                          /* nb_absolute */
+     Oid__bool,                  /* nb_bool */
+     0,                          /* nb_invert */
+     0,                          /* nb_lshift */
+     0,                          /* nb_rshift */
+     0,                          /* nb_and */
+     0,                          /* nb_xor */
+     0,                          /* nb_or */
+     0,                          /* nb_int */
+     0,                          /* nb_reserved */
+     0,                          /* nb_float */
+     0,                          /* nb_inplace_add */
+     0,                          /* nb_inplace_subtract */
+     0,                          /* nb_inplace_multiply */
+     0,                          /* nb_inplace_remainder */
+     0,                          /* nb_inplace_power */
+     0,                          /* nb_inplace_lshift */
+     0,                          /* nb_inplace_rshift */
+     0,                          /* nb_inplace_and */
+     0,                          /* nb_inplace_xor */
+     0,                          /* nb_inplace_or */
+     0,                          /* nb_floor_divide */
+     0,                          /* nb_true_divide */
+     0,                          /* nb_inplace_floor_divide */
+     0,                          /* nb_inplace_true_divide */
+     0,                          /* nb_index */
+     0,                          /* nb_matrix_multiply */
+     0,                          /* nb_inplace_matrix_multiply */
+};
+
 PyDoc_STRVAR(Oid__doc__, "Object id.");
 
 PyTypeObject OidType = {
@@ -282,7 +330,7 @@ PyTypeObject OidType = {
     0,                                         /* tp_setattr        */
     0,                                         /* tp_compare        */
     (reprfunc)Oid__str__,                      /* tp_repr           */
-    0,                                         /* tp_as_number      */
+    &Oid_as_number,                            /* tp_as_number      */
     0,                                         /* tp_as_sequence    */
     0,                                         /* tp_as_mapping     */
     (hashfunc)Oid_hash,                        /* tp_hash           */

test/test_oid.py

@@ -99,3 +99,10 @@ def test_hash():
     s.add(Oid(hex='0000000000000000000000000000000000000000'))
     s.add(Oid(hex='0000000000000000000000000000000000000001'))
     assert len(s) == 3
+
+
+def test_bool():
+    assert Oid(raw=RAW)
+    assert Oid(hex=HEX)
+    assert not Oid(raw=b'')
+    assert not Oid(hex='0000000000000000000000000000000000000000')