Distinguish char16_t.

bindgen-tests/tests/headers/char16_t.hpp

@@ -0,0 +1,4 @@
+// bindgen-flags: --use-distinct-char16-t --raw-line '#[repr(transparent)] pub struct bindgen_cchar16_t(u16);' -- -x c++ -std=c++14
+
+void receive_char16_t(char16_t input) {
+}

bindgen/codegen/helpers.rs

@@ -187,6 +187,12 @@ pub(crate) mod ast_ty {
         match ik {
             IntKind::Bool => syn::parse_quote! { bool },
             IntKind::Char { .. } => raw_type(ctx, "c_char"),
+            // The following is used only when an unusual command-line
+            // argument is used. bindgen_cchar16_t is not a real type;
+            // but this allows downstream postprocessors to distinguish
+            // this case and do something special for C++ bindings
+            // containing char16_t.
+            IntKind::Char16 => syn::parse_quote! { bindgen_cchar16_t },
             IntKind::SChar => raw_type(ctx, "c_schar"),
             IntKind::UChar => raw_type(ctx, "c_uchar"),
             IntKind::Short => raw_type(ctx, "c_short"),

bindgen/ir/context.rs

@@ -1980,6 +1980,9 @@ If you encounter an error missing from this list, please file an issue or a PR!"
             CXType_Short => TypeKind::Int(IntKind::Short),
             CXType_UShort => TypeKind::Int(IntKind::UShort),
             CXType_WChar => TypeKind::Int(IntKind::WChar),
+            CXType_Char16 if self.options().use_distinct_char16_t => {
+                TypeKind::Int(IntKind::Char16)
+            }
             CXType_Char16 => TypeKind::Int(IntKind::U16),
             CXType_Char32 => TypeKind::Int(IntKind::U32),
             CXType_Long => TypeKind::Int(IntKind::Long),

bindgen/ir/int.rs

@@ -54,9 +54,12 @@ pub enum IntKind {
     /// A 16-bit signed integer.
     I16,
 
-    /// Either a `char16_t` or a `wchar_t`.
+    /// A 16-bit integer, used only for enum size representation.
     U16,
 
+    /// Either a `char16_t` or a `wchar_t`.
+    Char16,
+
     /// A 32-bit signed integer.
     I32,
 
@@ -94,7 +97,7 @@ impl IntKind {
             // to know whether it is or not right now (unlike char, there's no
             // WChar_S / WChar_U).
             Bool | UChar | UShort | UInt | ULong | ULongLong | U8 | U16 |
-            WChar | U32 | U64 | U128 => false,
+            Char16 | WChar | U32 | U64 | U128 => false,
 
             SChar | Short | Int | Long | LongLong | I8 | I16 | I32 | I64 |
             I128 => true,
@@ -110,7 +113,7 @@ impl IntKind {
         use self::IntKind::*;
         Some(match *self {
             Bool | UChar | SChar | U8 | I8 | Char { .. } => 1,
-            U16 | I16 => 2,
+            U16 | I16 | Char16 => 2,
             U32 | I32 => 4,
             U64 | I64 => 8,
             I128 | U128 => 16,

bindgen/options/cli.rs

@@ -441,6 +441,9 @@ struct BindgenCommand {
     /// Always output explicit padding fields.
     #[arg(long)]
     explicit_padding: bool,
+    /// Use distinct char16_t
+    #[arg(long)]
+    use_distinct_char16_t: bool,
     /// Enables generation of vtable functions.
     #[arg(long)]
     vtable_generation: bool,
@@ -629,6 +632,7 @@ where
         translate_enum_integer_types,
         c_naming,
         explicit_padding,
+        use_distinct_char16_t,
         vtable_generation,
         sort_semantically,
         merge_extern_blocks,
@@ -926,6 +930,7 @@ where
             translate_enum_integer_types,
             c_naming,
             explicit_padding,
+            use_distinct_char16_t,
             vtable_generation,
             sort_semantically,
             merge_extern_blocks,

bindgen/options/mod.rs

@@ -153,6 +153,28 @@ macro_rules! options {
 }
 
 options! {
+    /// Whether we should distinguish between 'char16_t' and 'u16'.
+    /// As standard, bindgen represents `char16_t` as `u16`.
+    /// Rust does not have a `std::os::raw::c_char16_t` type, and thus
+    /// we can't use a built-in Rust type in the generated bindings.
+    /// But for some uses of bindgen, especially when downstream
+    /// post-processing occurs, it's important to distinguish `char16_t`
+    /// from normal `uint16_t`. When this option is enabled, bindgen
+    /// generates a fake type called `bindgen_cchar16_t`. Downstream
+    /// code post-processors should arrange to replace this with a
+    /// real type.
+    use_distinct_char16_t: bool {
+        methods: {
+            /// If this is true, denote 'char16_t' as a separate type from 'u16'
+            /// Disabled by default.
+            pub fn use_distinct_char16_t(mut self, doit: bool) -> Builder {
+                self.options.use_distinct_char16_t = doit;
+                self
+            }
+        },
+        as_args: "--use-distinct-char16-t",
+    },
+
     /// Types that have been blocklisted and should not appear anywhere in the generated code.
     blocklisted_types: RegexSet {
         methods: {