add --cxx flag

Author: pvdrz

book/src/cpp.md

@@ -7,9 +7,8 @@ be nowhere near as nice as using them in C++. You will have to manually call
 constructors, destructors, overloaded operators, etc yourself.
 
 When passing in header files, the file will automatically be treated as C++ if
-it ends in `.hpp`. If it doesn't, adding `-x c++` clang args can be used to
-force C++ mode. You probably also want to use `-std=c++14` or similar clang args
-as well.
+it ends in `.hpp`. If it doesn't, adding the `--cxx` flag will force C++ mode.
+You probably also want to use the clang arg `-std=c++14` or similar as well.
 
 You pretty much **must** use [allowlisting](./allowlisting.md) when working
 with C++ to avoid pulling in all of the `std::.*` types, many of which `bindgen`
@@ -71,8 +70,8 @@ cannot translate into Rust:
   generate undefined behaviour. See
   [the tracking issue for exceptions](https://github.com/rust-lang/rust-bindgen/issues/1208)
   for more details.
-  
+
 * Return value optimization. C++ compilers will in certain circumstances optimize functions
   returning a struct type value to instead take an extra hidden argument that refers
   to the return value struct. `bindgen` cannot necessarily know about this optimization and
-  thus at present `bindgen`-interfaces for these kinds of functions are invalid. 
+  thus at present `bindgen`-interfaces for these kinds of functions are invalid.

src/lib.rs

@@ -1323,6 +1323,12 @@ impl Builder {
         self
     }
 
+    /// Tell `clang` that the input files are `c++` files.
+    #[inline]
+    pub fn cxx(self) -> Builder {
+        self.clang_args(["-x", "c++"])
+    }
+
     /// Enable detecting must_use attributes on C functions.
     ///
     /// This is quite slow in some cases (see #1465), so it's disabled by

src/options.rs

@@ -563,6 +563,9 @@ where
             Arg::new("merge-extern-blocks")
                 .long("merge-extern-blocks")
                 .help("Deduplicates extern blocks."),
+            Arg::new("cxx")
+                .long("cxx")
+                .help("Enables parsing C++ headers."),
             Arg::new("V")
                 .long("version")
                 .help("Prints the version, and exits"),
@@ -1083,5 +1086,9 @@ where
         builder = builder.merge_extern_blocks(true);
     }
 
+    if matches.is_present("cxx") {
+        builder = builder.cxx();
+    }
+
     Ok((builder, output, verbose))
 }

tests/headers/dash_language.h

@@ -1,4 +1,4 @@
-// bindgen-flags: -- -x c++ --std=c++11
+// bindgen-flags: --cxx -- --std=c++11
 
 template<typename T>
 struct Foo {

tests/headers/dupe-enum-variant-in-namespace.h

@@ -1,4 +1,4 @@
-// bindgen-flags: --rustified-enum ".*" --enable-cxx-namespaces -- -x c++ -std=c++11
+// bindgen-flags: --rustified-enum ".*" --enable-cxx-namespaces --cxx -- -std=c++11
 
 namespace foo {
   enum class Bar : unsigned {

tests/headers/empty-enum.h

@@ -1,4 +1,4 @@
-// bindgen-flags: --rustified-enum '.*Rustified.*' --constified-enum-module '.*Module.*' -- -x c++ --std=c++14
+// bindgen-flags: --rustified-enum '.*Rustified.*' --constified-enum-module '.*Module.*' --cxx -- --std=c++14
 
 // Constified is default, so no flag for that.
 

tests/headers/packed-vtable.h

@@ -1,4 +1,4 @@
-// bindgen-flags: --raw-line '#![cfg(feature = "nightly")]' --rust-target 1.33 -- -x c++ -std=c++11
+// bindgen-flags: --raw-line '#![cfg(feature = "nightly")]' --rust-target 1.33 --cxx -- -std=c++11
 
 #pragma pack(1)