Added rework of arg/return typing

Author: timohl

include/pybind11/detail/descr.h

@@ -99,6 +99,13 @@ constexpr descr<1, Type> const_name() {
     return {'%'};
 }
 
+// Use a different name based on whether the parameter is used as input or output
+template <size_t N1, size_t N2>
+constexpr auto io_name(char const (&text1)[N1], char const (&text2)[N2]) {
+    return const_name("@") + const_name(text1) + const_name("@") + const_name(text2)
+           + const_name("@");
+}
+
 // If "_" is defined as a macro, py::detail::_ cannot be provided.
 // It is therefore best to use py::detail::const_name universally.
 // This block is for backward compatibility only.

include/pybind11/pybind11.h

@@ -440,6 +440,7 @@ class cpp_function : public function {
         std::string signature;
         size_t type_index = 0, arg_index = 0;
         bool is_starred = false;
+        bool is_return_value = false;
         for (const auto *pc = text; *pc != '\0'; ++pc) {
             const auto c = *pc;
 
@@ -493,7 +494,29 @@ class cpp_function : public function {
                 } else {
                     signature += detail::quote_cpp_type_name(detail::clean_type_id(t->name()));
                 }
+            } else if (c == '@') {
+                // Handle types that differ depending on whether they appear
+                // in an argument or a return value position
+                ++pc;
+                if (!is_return_value) {
+                    while (*pc && *pc != '@')
+                        signature += *pc++;
+                    if (*pc == '@')
+                        ++pc;
+                    while (*pc && *pc != '@')
+                        ++pc;
+                } else {
+                    while (*pc && *pc != '@')
+                        ++pc;
+                    if (*pc == '@')
+                        ++pc;
+                    while (*pc && *pc != '@')
+                        signature += *pc++;
+                }
             } else {
+                if (c == '-' && *(pc + 1) == '>') {
+                    is_return_value = true;
+                }
                 signature += c;
             }
         }

include/pybind11/stl/filesystem.h

@@ -106,9 +106,7 @@ struct path_caster {
         return true;
     }
 
-    PYBIND11_TYPE_CASTER(T, const_name("os.PathLike"));
-    static constexpr auto arg_name = const_name("Union[os.PathLike, str, bytes]");
-    static constexpr auto return_name = const_name("Path");
+    PYBIND11_TYPE_CASTER(T, io_name("Union[os.PathLike, str, bytes]", "Path"));
 };
 
 #endif // PYBIND11_HAS_FILESYSTEM || defined(PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM)

tests/test_stl.py

@@ -267,11 +267,11 @@ def __fspath__(self):
         doc(m.parent_path)
         == "parent_path(arg0: Union[os.PathLike, str, bytes]) -> Path"
     )
-    # std::vector should use name (for arg_name/return_name typing classes must be used)
+    # std::vector
     assert m.parent_paths(["foo/bar", "foo/baz"]) == [Path("foo"), Path("foo")]
     assert (
         doc(m.parent_paths)
-        == "parent_paths(arg0: list[os.PathLike]) -> list[os.PathLike]"
+        == "parent_paths(arg0: list[Union[os.PathLike, str, bytes]]) -> list[Path]"
     )
     # py::typing::List
     assert m.parent_paths_list(["foo/bar", "foo/baz"]) == [Path("foo"), Path("foo")]