From 1bbb284ad1ba270be165c576be736bfddae094f2 Mon Sep 17 00:00:00 2001
From: PJ Reiniger <pj.reiniger@gmail.com>
Date: Wed, 31 Dec 2025 12:03:24 -0500
Subject: [PATCH] [py][wpiutil] Add type caster for WPI_String (#8500)

This adds a type caster for `WPI_String` so that pybind11 can more
easily auto-convert between that and strings. This helps remove the need
to do things like
[this](https://github.com/wpilibsuite/allwpilib/pull/8498/commits/f1d77244c3c78a4777798068c8a2b8dd4dc83339)
in the opmodes fixup
---
 wpiutil/src/main/python/pyproject.toml        |  4 +++
 .../src/type_casters/wpi_string_type_caster.h | 34 +++++++++++++++++++
 .../test/python/cpp/wpiutil_test/module.cpp   | 33 ++++++++++++++++++
 wpiutil/src/test/python/test_wpi_string.py    | 15 ++++++++
 4 files changed, 86 insertions(+)
 create mode 100644 wpiutil/src/main/python/wpiutil/src/type_casters/wpi_string_type_caster.h
 create mode 100644 wpiutil/src/test/python/test_wpi_string.py

diff --git a/wpiutil/src/main/python/pyproject.toml b/wpiutil/src/main/python/pyproject.toml
index 9591848853..e90ce9c031 100644
--- a/wpiutil/src/main/python/pyproject.toml
+++ b/wpiutil/src/main/python/pyproject.toml
@@ -120,6 +120,10 @@ types = ["wpi::util::StringMap"]
 header = "wpi_ct_string_type_caster.h"
 types = ["wpi::util::ct_string"]
 
+[[tool.semiwrap.export_type_casters.wpiutil-casters.headers]]
+header = "wpi_string_type_caster.h"
+types = ["WPI_String"]
+
 [[tool.semiwrap.export_type_casters.wpiutil-casters.headers]]
 header = "wpystruct.h"
 types = ["WPyStruct"]
diff --git a/wpiutil/src/main/python/wpiutil/src/type_casters/wpi_string_type_caster.h b/wpiutil/src/main/python/wpiutil/src/type_casters/wpi_string_type_caster.h
new file mode 100644
index 0000000000..abb17adaf7
--- /dev/null
+++ b/wpiutil/src/main/python/wpiutil/src/type_casters/wpi_string_type_caster.h
@@ -0,0 +1,34 @@
+#include <pybind11/pybind11.h>
+
+#include "wpi/util/string.h"
+
+namespace pybind11::detail {
+
+template <> 
+struct type_caster<WPI_String> {
+public:
+    PYBIND11_TYPE_CASTER(WPI_String, _("str"));
+
+    bool load(handle src, bool convert) {
+        if (!src) {
+            return false;
+        }
+
+        Py_ssize_t size = -1;
+        const char *str = PyUnicode_AsUTF8AndSize(src.ptr(), &size);
+        if (!str) {
+            PyErr_Clear();
+            return false;
+        }
+
+        value = WPI_String(str, static_cast<size_t>(size));
+        
+        return true;
+    }
+
+    static handle cast(const WPI_String& str, return_value_policy /* policy */, handle /* parent */) {
+        return PyUnicode_FromStringAndSize(str.str, str.len);
+    }
+};
+
+} // namespace pybind11::detail
\ No newline at end of file
diff --git a/wpiutil/src/test/python/cpp/wpiutil_test/module.cpp b/wpiutil/src/test/python/cpp/wpiutil_test/module.cpp
index 8eb61211ea..2cef396bc3 100644
--- a/wpiutil/src/test/python/cpp/wpiutil_test/module.cpp
+++ b/wpiutil/src/test/python/cpp/wpiutil_test/module.cpp
@@ -9,6 +9,7 @@
 #include <wpi_string_map_caster.h>
 #include <wpi_json_type_caster.h>
 #include <wpi_ct_string_type_caster.h>
+#include <wpi_string_type_caster.h>
 
 #include <limits>
 #include <functional>
@@ -152,6 +153,29 @@ constexpr auto const_string() {
 void sendable_test(py::module &m);
 void struct_test(py::module &m);
 
+/* WPI_String tests */
+struct StructWithWPI_String {
+    int x;
+    WPI_String str;
+};
+
+WPI_String load_wpi_string(WPI_String str) {
+    return str;
+}
+
+WPI_String cast_wpi_string() {
+    WPI_String str = wpi::util::make_string("Hello WPI_String!");
+    return str;
+}
+
+StructWithWPI_String cast_struct_with_wpi_string() {
+    StructWithWPI_String output{
+        .x = 3504,
+        .str = wpi::util::make_string("I'm in a struct!")
+    };
+
+    return output;
+}
 
 PYBIND11_MODULE(module, m) {
 
@@ -192,4 +216,13 @@ PYBIND11_MODULE(module, m) {
     m.attr("min_int64") = std::numeric_limits<int64_t>::min();
     // ct_string
     m.def("const_string", &const_string);
+
+    // WPI_String
+    m.def("load_wpi_string", &load_wpi_string);
+    m.def("cast_wpi_string", &cast_wpi_string);
+    
+    py::class_<StructWithWPI_String> structWithWpiStringCls(m, "StructWithWPI_String");
+    structWithWpiStringCls.def_readwrite("x", &StructWithWPI_String::x);
+    structWithWpiStringCls.def_readonly("str", &StructWithWPI_String::str);
+    m.def("cast_struct_with_wpi_string", &cast_struct_with_wpi_string);
 };
diff --git a/wpiutil/src/test/python/test_wpi_string.py b/wpiutil/src/test/python/test_wpi_string.py
new file mode 100644
index 0000000000..719252835d
--- /dev/null
+++ b/wpiutil/src/test/python/test_wpi_string.py
@@ -0,0 +1,15 @@
+from wpiutil_test import module
+
+
+def test_wpi_string_load():
+    assert "Hello World" == module.load_wpi_string("Hello World")
+
+
+def test_wpi_string_cast():
+    assert "Hello WPI_String!" == module.cast_wpi_string()
+
+
+def test_wpi_string_in_struct_cast():
+    the_struct = module.cast_struct_with_wpi_string()
+    assert 3504 == the_struct.x
+    assert "I'm in a struct!" == the_struct.str