chore: drop support for PyPy < 7.3.1 and clean up old PyPy workarounds (#2456)

* Remove code inside 'PYPY_VERSION_NUM < 0x06000000' preprocessor if branch

* fix: more cleanup

* Remove more references to PyPy 5.7 and 5.9 in the docs

* Update comment on PyUnicode_UTF* in PyPy
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

README.rst

@@ -68,7 +68,7 @@ Goodies
 In addition to the core functionality, pybind11 provides some extra
 goodies:
 
--  Python 2.7, 3.5+, and PyPy (tested on 7.3) are supported with an
+-  Python 2.7, 3.5+, and PyPy/PyPy3 7.3 are supported with an
    implementation-agnostic interface.
 
 -  It is possible to bind C++11 lambda functions with captured

docs/advanced/misc.rst

@@ -223,7 +223,7 @@ avoids this issue involves weak reference with a cleanup callback:
 
 .. code-block:: cpp
 
-    // Register a callback function that is invoked when the BaseClass object is colelcted
+    // Register a callback function that is invoked when the BaseClass object is collected
     py::cpp_function cleanup_callback(
         [](py::handle weakref) {
             // perform cleanup here -- this function is called with the GIL held
@@ -237,9 +237,9 @@ avoids this issue involves weak reference with a cleanup callback:
 
 .. note::
 
-    PyPy (at least version 5.9) does not garbage collect objects when the
-    interpreter exits. An alternative approach (which also works on CPython) is to use
-    the :py:mod:`atexit` module [#f7]_, for example:
+    PyPy does not garbage collect objects when the interpreter exits. An alternative
+    approach (which also works on CPython) is to use the :py:mod:`atexit` module [#f7]_,
+    for example:
 
     .. code-block:: cpp
 

include/pybind11/cast.h

@@ -1277,10 +1277,8 @@ private:
             UTF_N == 16 ? PyUnicode_DecodeUTF16(buffer, nbytes, nullptr, nullptr) :
                           PyUnicode_DecodeUTF32(buffer, nbytes, nullptr, nullptr);
 #else
-        // PyPy seems to have multiple problems related to PyUnicode_UTF*: the UTF8 version
-        // sometimes segfaults for unknown reasons, while the UTF16 and 32 versions require a
-        // non-const char * arguments, which is also a nuisance, so bypass the whole thing by just
-        // passing the encoding as a string value, which works properly:
+        // PyPy segfaults when on PyUnicode_DecodeUTF16 (and possibly on PyUnicode_DecodeUTF32 as well),
+        // so bypass the whole thing by just passing the encoding as a string value, which works properly:
         return PyUnicode_Decode(buffer, nbytes, UTF_N == 8 ? "utf-8" : UTF_N == 16 ? "utf-16" : "utf-32", nullptr);
 #endif
     }

include/pybind11/detail/class.h

@@ -478,10 +478,6 @@ extern "C" inline int pybind11_clear(PyObject *self) {
 /// Give instances of this type a `__dict__` and opt into garbage collection.
 inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
     auto type = &heap_type->ht_type;
-#if defined(PYPY_VERSION) && (PYPY_VERSION_NUM < 0x06000000)
-    pybind11_fail(get_fully_qualified_tp_name(type) + ": dynamic attributes are currently not "
-                                                      "supported in conjunction with PyPy!");
-#endif
     type->tp_flags |= Py_TPFLAGS_HAVE_GC;
     type->tp_dictoffset = type->tp_basicsize; // place dict at the end
     type->tp_basicsize += (ssize_t)sizeof(PyObject *); // and allocate enough space for it

include/pybind11/eval.h

@@ -66,7 +66,7 @@ void exec(const char (&s)[N], object global = globals(), object local = object()
     eval<eval_statements>(s, global, local);
 }
 
-#if defined(PYPY_VERSION) && PY_VERSION_HEX >= 0x3000000
+#if defined(PYPY_VERSION) && PY_VERSION_HEX >= 0x03000000
 template <eval_mode mode = eval_statements>
 object eval_file(str, object, object) {
     pybind11_fail("eval_file not supported in PyPy3. Use eval");

tests/test_multiple_inheritance.cpp

@@ -193,14 +193,12 @@ TEST_SUBMODULE(multiple_inheritance, m) {
         .def_readwrite_static("static_value", &VanillaStaticMix2::static_value);
 
 
-#if !(defined(PYPY_VERSION) && (PYPY_VERSION_NUM < 0x06000000))
     struct WithDict { };
     struct VanillaDictMix1 : Vanilla, WithDict { };
     struct VanillaDictMix2 : WithDict, Vanilla { };
     py::class_<WithDict>(m, "WithDict", py::dynamic_attr()).def(py::init<>());
     py::class_<VanillaDictMix1, Vanilla, WithDict>(m, "VanillaDictMix1").def(py::init<>());
     py::class_<VanillaDictMix2, WithDict, Vanilla>(m, "VanillaDictMix2").def(py::init<>());
-#endif
 
     // test_diamond_inheritance
     // Issue #959: segfault when constructing diamond inheritance instance