ir: Treat char8_t as a u8 builtin

CHANGELOG.md

@@ -254,6 +254,7 @@
 - Fixed a panic when generating bindings for Objective-C methods that declare C-style parameters (#3488).
 - Fixed a panic when an Objective-C method returns `Class`. The `Class` type is now generated as `*mut objc::runtime::Class` instead of an interface named after the enclosing declaration (#3484).
 - Fixed a stack overflow when generating bindings for nested alias template instantiations such as `U<U<int>>` (#3478).
+- Fixed a panic when generating bindings for C++20 `char8_t` arrays. `char8_t` is now always generated as `u8`, so enums with a `char8_t` underlying type are unsigned too (#3474, #3464).
 
 ## Security
 

bindgen-tests/tests/headers/char8_t.hpp

@@ -0,0 +1,18 @@
+// bindgen-flags: -- -std=c++20
+
+extern char8_t global_array[4];
+extern char8_t incomplete_array[];
+extern char8_t nested_array[2][2];
+
+struct WithChar8Array {
+  char8_t bytes[8];
+  char8_t single;
+};
+
+void take_char8_array(char8_t input[4]);
+char8_t return_char8(char8_t input);
+
+enum class Char8Enum : char8_t {
+  High = 0xFF,
+  Low = 0x41,
+};

bindgen/ir/context.rs

@@ -2024,6 +2024,17 @@ If you encounter an error missing from this list, please file an issue or a PR!"
             }
             CXType_Char16 => TypeKind::Int(IntKind::U16),
             CXType_Char32 => TypeKind::Int(IntKind::U32),
+            // libclang has no CXType_Char8, so char8_t shows up as unexposed.
+            CXType_Unexposed
+                if ty
+                    .canonical_type()
+                    .spelling()
+                    .split_whitespace()
+                    .filter(|part| !matches!(*part, "const" | "volatile"))
+                    .eq(["char8_t"]) =>
+            {
+                TypeKind::Int(IntKind::U8)
+            }
             CXType_Long => TypeKind::Int(IntKind::Long),
             CXType_ULong => TypeKind::Int(IntKind::ULong),
             CXType_LongLong => TypeKind::Int(IntKind::LongLong),