Mirror c_char configuration from rust-lang/rust

Create a module providing the same definitions of `c_char` as in
`rust-lang/rust`, which in most cases are based on the architecture
rather than the OS. This will allow individual platforms to reexport the
definition rather than having configuration repeated in numerous
modules.

(backport <#4198>)
(cherry picked from commit 28d4064)

libc-test/build.rs

@@ -364,6 +364,9 @@ fn test_apple(target: &str) {
             // FIXME: "'__uint128' undeclared" in C
             "__uint128" => true,
 
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
+
             _ => false,
         }
     });
@@ -758,6 +761,8 @@ fn test_windows(target: &str) {
         "ssize_t" if !gnu => true,
         // FIXME: The size and alignment of this type are incorrect
         "time_t" if gnu && i686 => true,
+        // `c_char_def` is always public but not always reexported.
+        "c_char_def" => true,
         _ => false,
     });
 
@@ -975,6 +980,8 @@ fn test_solarish(target: &str) {
 
     cfg.skip_type(move |ty| match ty {
         "sighandler_t" => true,
+        // `c_char_def` is always public but not always reexported.
+        "c_char_def" => true,
         _ => false,
     });
 
@@ -1278,6 +1285,8 @@ fn test_netbsd(target: &str) {
         match ty {
             // FIXME: sighandler_t is crazy across platforms
             "sighandler_t" => true,
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
             _ => false,
         }
     });
@@ -1497,7 +1506,8 @@ fn test_dragonflybsd(target: &str) {
         match ty {
             // sighandler_t is crazy across platforms
             "sighandler_t" => true,
-
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
             _ => false,
         }
     });
@@ -1659,6 +1669,8 @@ fn test_wasi(target: &str) {
         }
     });
 
+    cfg.skip_type(|ty| ty == "c_char_def");
+
     // These have a different and internal type in header files and are only
     // used here to generate a pointer to them in bindings so skip these tests.
     cfg.skip_static(|c| c.starts_with("_CLOCK_"));
@@ -1907,6 +1919,9 @@ fn test_android(target: &str) {
             // FIXME: "'__uint128' undeclared" in C
             "__uint128" => true,
 
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
+
             _ => false,
         }
     });
@@ -2669,6 +2684,9 @@ fn test_freebsd(target: &str) {
             // `eventfd(2)` and things come with it are added in FreeBSD 13
             "eventfd_t" if Some(13) > freebsd_ver => true,
 
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
+
             _ => false,
         }
     });
@@ -2989,6 +3007,9 @@ fn test_emscripten(target: &str) {
             // https://github.com/emscripten-core/emscripten/issues/5033
             ty if ty.starts_with("epoll") => true,
 
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
+
             // LFS64 types have been removed in Emscripten 3.1.44
             // https://github.com/emscripten-core/emscripten/pull/19812
             t => t.ends_with("64") || t.ends_with("64_t"),
@@ -3260,6 +3281,9 @@ fn test_neutrino(target: &str) {
             // Does not exist in Neutrino
             "locale_t" => true,
 
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
+
             _ => false,
         }
     });
@@ -3426,6 +3450,8 @@ fn test_vxworks(target: &str) {
     // FIXME
     cfg.skip_type(move |ty| match ty {
         "stat64" | "sighandler_t" | "off64_t" => true,
+        // `c_char_def` is always public but not always reexported.
+        "c_char_def" => true,
         _ => false,
     });
 
@@ -3773,6 +3799,9 @@ fn test_linux(target: &str) {
             // FIXME: "'__uint128' undeclared" in C
             "__uint128" => true,
 
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
+
             t => {
                 if musl {
                     // LFS64 types have been removed in musl 1.2.4+
@@ -4725,6 +4754,8 @@ fn test_linux_like_apis(target: &str) {
             })
             .skip_type(move |ty| match ty {
                 "Elf64_Phdr" | "Elf32_Phdr" => false,
+                // `c_char_def` is always public but not always reexported.
+                "c_char_def" => true,
                 _ => true,
             });
         cfg.generate(src_hotfix_dir().join("lib.rs"), "linux_elf.rs");
@@ -4960,6 +4991,8 @@ fn test_haiku(target: &str) {
             "pthread_condattr_t" => true,
             "pthread_mutexattr_t" => true,
             "pthread_rwlockattr_t" => true,
+            // `c_char_def` is always public but not always reexported.
+            "c_char_def" => true,
             _ => false,
         }
     });

src/lib.rs

@@ -41,6 +41,44 @@ cfg_if! {
 
 pub use core::ffi::c_void;
 
+/// Type definitions that are coupled tighter to architecture than OS.
+mod arch {
+    cfg_if! {
+        // This configuration comes from `rust-lang/rust` in `library/core/src/ffi/mod.rs`.
+        if #[cfg(all(
+            not(windows),
+            // FIXME(ctest): just use `target_vendor` = "apple"` once `ctest` supports it
+            not(any(
+                target_os = "macos",
+                target_os = "ios",
+                target_os = "tvos",
+                target_os = "watchos",
+                target_os = "visionos",
+            )),
+            any(
+                target_arch = "aarch64",
+                target_arch = "arm",
+                target_arch = "csky",
+                target_arch = "hexagon",
+                target_arch = "msp430",
+                target_arch = "powerpc",
+                target_arch = "powerpc64",
+                target_arch = "riscv64",
+                target_arch = "riscv32",
+                target_arch = "s390x",
+                target_arch = "xtensa",
+            )
+        ))] {
+            // To be reexported as `c_char`
+            // FIXME(ctest): just name these `c_char` once `ctest` learns that these don't get
+            // exported.
+            pub type c_char_def = u8;
+        } else {
+            pub type c_char_def = i8;
+        }
+    }
+}
+
 cfg_if! {
     if #[cfg(windows)] {
         mod fixed_width_ints;