Update tests to use c_char where appropriate

tests/BUCK

@@ -12,6 +12,7 @@ rust_test(
 rust_library(
     name = "ffi",
     srcs = [
+        "ffi/cast.rs",
         "ffi/lib.rs",
         "ffi/module.rs",
     ],

tests/BUILD

@@ -15,6 +15,7 @@ rust_test(
 rust_library(
     name = "cxx_test_suite",
     srcs = [
+        "ffi/cast.rs",
         "ffi/lib.rs",
         "ffi/module.rs",
     ],

tests/ffi/cast.rs

@@ -0,0 +1,14 @@
+use std::os::raw::c_char;
+use std::slice;
+
+pub fn c_char_to_unsigned(slice: &[c_char]) -> &[u8] {
+    let ptr = slice.as_ptr().cast::<u8>();
+    let len = slice.len();
+    unsafe { slice::from_raw_parts(ptr, len) }
+}
+
+pub fn unsigned_to_c_char(slice: &[u8]) -> &[c_char] {
+    let ptr = slice.as_ptr().cast::<c_char>();
+    let len = slice.len();
+    unsafe { slice::from_raw_parts(ptr, len) }
+}

tests/ffi/lib.rs

@@ -6,10 +6,12 @@
     clippy::unnecessary_wraps
 )]
 
+pub mod cast;
 pub mod module;
 
 use cxx::{CxxString, CxxVector, UniquePtr};
 use std::fmt::{self, Display};
+use std::os::raw::c_char;
 
 #[cxx::bridge(namespace = "tests")]
 pub mod ffi {
@@ -81,7 +83,7 @@ pub mod ffi {
         fn c_return_ref(shared: &Shared) -> &usize;
         fn c_return_mut(shared: &mut Shared) -> &mut usize;
         fn c_return_str(shared: &Shared) -> &str;
-        fn c_return_sliceu8(shared: &Shared) -> &[u8];
+        fn c_return_slice_char(shared: &Shared) -> &[c_char];
         fn c_return_mutsliceu8(slice: &mut [u8]) -> &mut [u8];
         fn c_return_rust_string() -> String;
         fn c_return_unique_ptr_string() -> UniquePtr<CxxString>;
@@ -110,7 +112,7 @@ pub mod ffi {
         fn c_take_ref_r(r: &R);
         fn c_take_ref_c(c: &C);
         fn c_take_str(s: &str);
-        fn c_take_sliceu8(s: &[u8]);
+        fn c_take_slice_char(s: &[c_char]);
         fn c_take_slice_shared(s: &[Shared]);
         fn c_take_rust_string(s: String);
         fn c_take_unique_ptr_string(s: UniquePtr<CxxString>);
@@ -214,7 +216,7 @@ pub mod ffi {
         fn r_take_ref_r(r: &R);
         fn r_take_ref_c(c: &C);
         fn r_take_str(s: &str);
-        fn r_take_sliceu8(s: &[u8]);
+        fn r_take_slice_char(s: &[c_char]);
         fn r_take_rust_string(s: String);
         fn r_take_unique_ptr_string(s: UniquePtr<CxxString>);
         fn r_take_ref_vector(v: &CxxVector<u8>);
@@ -472,8 +474,9 @@ fn r_take_rust_string(s: String) {
     assert_eq!(s, "2020");
 }
 
-fn r_take_sliceu8(s: &[u8]) {
+fn r_take_slice_char(s: &[c_char]) {
     assert_eq!(s.len(), 5);
+    let s = cast::c_char_to_unsigned(s);
     assert_eq!(std::str::from_utf8(s).unwrap(), "2020\0");
 }
 

tests/ffi/tests.cc

@@ -75,10 +75,9 @@ rust::Str c_return_str(const Shared &shared) {
   return "2020";
 }
 
-rust::Slice<const uint8_t> c_return_sliceu8(const Shared &shared) {
+rust::Slice<const char> c_return_slice_char(const Shared &shared) {
   (void)shared;
-  return rust::Slice<const uint8_t>(
-      reinterpret_cast<const uint8_t *>(SLICE_DATA), sizeof(SLICE_DATA));
+  return rust::Slice<const char>(SLICE_DATA, sizeof(SLICE_DATA));
 }
 
 rust::Slice<uint8_t> c_return_mutsliceu8(rust::Slice<uint8_t> slice) {
@@ -243,9 +242,8 @@ void c_take_str(rust::Str s) {
   }
 }
 
-void c_take_sliceu8(rust::Slice<const uint8_t> s) {
-  if (std::string(reinterpret_cast<const char *>(s.data()), s.size()) ==
-      "2020") {
+void c_take_slice_char(rust::Slice<const char> s) {
+  if (std::string(s.data(), s.size()) == "2020") {
     cxx_test_suite_set_correct();
   }
 }
@@ -626,8 +624,7 @@ extern "C" const char *cxx_run_test() noexcept {
   r_take_unique_ptr(std::unique_ptr<C>(new C{2020}));
   r_take_ref_c(C{2020});
   r_take_str(rust::Str("2020"));
-  r_take_sliceu8(rust::Slice<const uint8_t>(
-      reinterpret_cast<const uint8_t *>(SLICE_DATA), sizeof(SLICE_DATA)));
+  r_take_slice_char(rust::Slice<const char>(SLICE_DATA, sizeof(SLICE_DATA)));
   r_take_rust_string(rust::String("2020"));
   r_take_unique_ptr_string(
       std::unique_ptr<std::string>(new std::string("2020")));

tests/ffi/tests.h

@@ -83,7 +83,7 @@ const size_t &c_return_ns_ref(const ::A::AShared &shared);
 const size_t &c_return_nested_ns_ref(const ::A::B::ABShared &shared);
 size_t &c_return_mut(Shared &shared);
 rust::Str c_return_str(const Shared &shared);
-rust::Slice<const uint8_t> c_return_sliceu8(const Shared &shared);
+rust::Slice<const char> c_return_slice_char(const Shared &shared);
 rust::Slice<uint8_t> c_return_mutsliceu8(rust::Slice<uint8_t> slice);
 rust::String c_return_rust_string();
 std::unique_ptr<std::string> c_return_unique_ptr_string();
@@ -114,7 +114,7 @@ void c_take_ref_r(const R &r);
 void c_take_ref_c(const C &c);
 void c_take_ref_ns_c(const ::H::H &h);
 void c_take_str(rust::Str s);
-void c_take_sliceu8(rust::Slice<const uint8_t> s);
+void c_take_slice_char(rust::Slice<const char> s);
 void c_take_slice_shared(rust::Slice<const Shared> s);
 void c_take_rust_string(rust::String s);
 void c_take_unique_ptr_string(std::unique_ptr<std::string> s);

tests/test.rs

@@ -1,7 +1,7 @@
 #![allow(clippy::assertions_on_constants, clippy::float_cmp, clippy::unit_cmp)]
 
 use cxx_test_suite::module::ffi2;
-use cxx_test_suite::{ffi, R};
+use cxx_test_suite::{cast, ffi, R};
 use std::cell::Cell;
 use std::ffi::CStr;
 
@@ -41,7 +41,10 @@ fn test_c_return() {
     assert_eq!(2020, *ffi::c_return_ns_ref(&ns_shared));
     assert_eq!(2020, *ffi::c_return_nested_ns_ref(&nested_ns_shared));
     assert_eq!("2020", ffi::c_return_str(&shared));
-    assert_eq!(b"2020\0", ffi::c_return_sliceu8(&shared));
+    assert_eq!(
+        b"2020\0",
+        cast::c_char_to_unsigned(ffi::c_return_slice_char(&shared)),
+    );
     assert_eq!("2020", ffi::c_return_rust_string());
     assert_eq!("2020", ffi::c_return_unique_ptr_string().to_str().unwrap());
     assert_eq!(4, ffi::c_return_unique_ptr_vector_u8().len());
@@ -116,7 +119,7 @@ fn test_c_take() {
     check!(ffi2::c_take_ref_ns_c(&unique_ptr_ns));
     check!(cxx_test_suite::module::ffi::c_take_unique_ptr(unique_ptr));
     check!(ffi::c_take_str("2020"));
-    check!(ffi::c_take_sliceu8(b"2020"));
+    check!(ffi::c_take_slice_char(cast::unsigned_to_c_char(b"2020")));
     check!(ffi::c_take_slice_shared(&[
         ffi::Shared { z: 2020 },
         ffi::Shared { z: 2021 },