Make postprocessing more robust

This is done by merging extern blocks and sorting items in every module
instead of just in the root module.

The tests were changed to use `cxx` namespaces so they effectively check
that items are manipulated correctly in every single module.

12 files changed, 681 insertions, 208 deletions

diff --git a/bindgen-tests/tests/expectations/tests/merge-extern-blocks.rs b/bindgen-tests/tests/expectations/tests/merge-extern-blocks.rs
index 66ceeff0..ae9799d2 100644
--- a/bindgen-tests/tests/expectations/tests/merge-extern-blocks.rs
+++ b/bindgen-tests/tests/expectations/tests/merge-extern-blocks.rs
@@ -5,33 +5,88 @@
     non_upper_case_globals
 )]
 
-#[repr(C)]
-#[derive(Debug, Default, Copy, Clone)]
-pub struct Point {
-    pub x: ::std::os::raw::c_int,
-}
-#[test]
-fn bindgen_test_layout_Point() {
-    const UNINIT: ::std::mem::MaybeUninit<Point> =
-        ::std::mem::MaybeUninit::uninit();
-    let ptr = UNINIT.as_ptr();
-    assert_eq!(
-        ::std::mem::size_of::<Point>(),
-        4usize,
-        concat!("Size of: ", stringify!(Point))
-    );
-    assert_eq!(
-        ::std::mem::align_of::<Point>(),
-        4usize,
-        concat!("Alignment of ", stringify!(Point))
-    );
-    assert_eq!(
-        unsafe { ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize },
-        0usize,
-        concat!("Offset of field: ", stringify!(Point), "::", stringify!(x))
-    );
-}
-extern "C" {
-    pub fn foo() -> ::std::os::raw::c_int;
-    pub fn bar() -> ::std::os::raw::c_int;
+#[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
+pub mod root {
+    #[allow(unused_imports)]
+    use self::super::root;
+    #[repr(C)]
+    #[derive(Debug, Default, Copy, Clone)]
+    pub struct Point {
+        pub x: ::std::os::raw::c_int,
+    }
+    #[test]
+    fn bindgen_test_layout_Point() {
+        const UNINIT: ::std::mem::MaybeUninit<Point> =
+            ::std::mem::MaybeUninit::uninit();
+        let ptr = UNINIT.as_ptr();
+        assert_eq!(
+            ::std::mem::size_of::<Point>(),
+            4usize,
+            concat!("Size of: ", stringify!(Point))
+        );
+        assert_eq!(
+            ::std::mem::align_of::<Point>(),
+            4usize,
+            concat!("Alignment of ", stringify!(Point))
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize },
+            0usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Point),
+                "::",
+                stringify!(x)
+            )
+        );
+    }
+    pub mod ns {
+        #[allow(unused_imports)]
+        use self::super::super::root;
+        #[repr(C)]
+        #[derive(Debug, Default, Copy, Clone)]
+        pub struct Point {
+            pub x: ::std::os::raw::c_int,
+        }
+        #[test]
+        fn bindgen_test_layout_Point() {
+            const UNINIT: ::std::mem::MaybeUninit<Point> =
+                ::std::mem::MaybeUninit::uninit();
+            let ptr = UNINIT.as_ptr();
+            assert_eq!(
+                ::std::mem::size_of::<Point>(),
+                4usize,
+                concat!("Size of: ", stringify!(Point))
+            );
+            assert_eq!(
+                ::std::mem::align_of::<Point>(),
+                4usize,
+                concat!("Alignment of ", stringify!(Point))
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize
+                },
+                0usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Point),
+                    "::",
+                    stringify!(x)
+                )
+            );
+        }
+        extern "C" {
+            #[link_name = "\u{1}_ZN2ns3fooEv"]
+            pub fn foo() -> ::std::os::raw::c_int;
+            #[link_name = "\u{1}_ZN2ns3barEv"]
+            pub fn bar() -> ::std::os::raw::c_int;
+        }
+    }
+    extern "C" {
+        #[link_name = "\u{1}_Z3foov"]
+        pub fn foo() -> ::std::os::raw::c_int;
+        #[link_name = "\u{1}_Z3barv"]
+        pub fn bar() -> ::std::os::raw::c_int;
+    }
 }
diff --git a/bindgen-tests/tests/expectations/tests/sort-items.rs b/bindgen-tests/tests/expectations/tests/sort-items.rs
new file mode 100644
index 00000000..e04e3b60
--- /dev/null
+++ b/bindgen-tests/tests/expectations/tests/sort-items.rs
@@ -0,0 +1,220 @@
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
+pub mod root {
+    pub type number = ::std::os::raw::c_int;
+    #[repr(C)]
+    #[derive(Debug, Default, Copy, Clone)]
+    pub struct Point {
+        pub x: root::number,
+        pub y: root::number,
+    }
+    #[repr(C)]
+    #[derive(Debug, Default, Copy, Clone)]
+    pub struct Angle {
+        pub a: root::number,
+        pub b: root::number,
+    }
+    pub const NUMBER: root::number = 42;
+    #[test]
+    fn bindgen_test_layout_Point() {
+        const UNINIT: ::std::mem::MaybeUninit<Point> =
+            ::std::mem::MaybeUninit::uninit();
+        let ptr = UNINIT.as_ptr();
+        assert_eq!(
+            ::std::mem::size_of::<Point>(),
+            8usize,
+            concat!("Size of: ", stringify!(Point))
+        );
+        assert_eq!(
+            ::std::mem::align_of::<Point>(),
+            4usize,
+            concat!("Alignment of ", stringify!(Point))
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize },
+            0usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Point),
+                "::",
+                stringify!(x)
+            )
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).y) as usize - ptr as usize },
+            4usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Point),
+                "::",
+                stringify!(y)
+            )
+        );
+    }
+    #[test]
+    fn bindgen_test_layout_Angle() {
+        const UNINIT: ::std::mem::MaybeUninit<Angle> =
+            ::std::mem::MaybeUninit::uninit();
+        let ptr = UNINIT.as_ptr();
+        assert_eq!(
+            ::std::mem::size_of::<Angle>(),
+            8usize,
+            concat!("Size of: ", stringify!(Angle))
+        );
+        assert_eq!(
+            ::std::mem::align_of::<Angle>(),
+            4usize,
+            concat!("Alignment of ", stringify!(Angle))
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).a) as usize - ptr as usize },
+            0usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Angle),
+                "::",
+                stringify!(a)
+            )
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).b) as usize - ptr as usize },
+            4usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Angle),
+                "::",
+                stringify!(b)
+            )
+        );
+    }
+    pub mod ns {
+        pub type number = ::std::os::raw::c_int;
+        #[repr(C)]
+        #[derive(Debug, Default, Copy, Clone)]
+        pub struct Point {
+            pub x: root::ns::number,
+            pub y: root::ns::number,
+        }
+        #[repr(C)]
+        #[derive(Debug, Default, Copy, Clone)]
+        pub struct Angle {
+            pub a: root::ns::number,
+            pub b: root::ns::number,
+        }
+        pub const NUMBER: root::ns::number = 42;
+        #[test]
+        fn bindgen_test_layout_Point() {
+            const UNINIT: ::std::mem::MaybeUninit<Point> =
+                ::std::mem::MaybeUninit::uninit();
+            let ptr = UNINIT.as_ptr();
+            assert_eq!(
+                ::std::mem::size_of::<Point>(),
+                8usize,
+                concat!("Size of: ", stringify!(Point))
+            );
+            assert_eq!(
+                ::std::mem::align_of::<Point>(),
+                4usize,
+                concat!("Alignment of ", stringify!(Point))
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize
+                },
+                0usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Point),
+                    "::",
+                    stringify!(x)
+                )
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).y) as usize - ptr as usize
+                },
+                4usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Point),
+                    "::",
+                    stringify!(y)
+                )
+            );
+        }
+        #[test]
+        fn bindgen_test_layout_Angle() {
+            const UNINIT: ::std::mem::MaybeUninit<Angle> =
+                ::std::mem::MaybeUninit::uninit();
+            let ptr = UNINIT.as_ptr();
+            assert_eq!(
+                ::std::mem::size_of::<Angle>(),
+                8usize,
+                concat!("Size of: ", stringify!(Angle))
+            );
+            assert_eq!(
+                ::std::mem::align_of::<Angle>(),
+                4usize,
+                concat!("Alignment of ", stringify!(Angle))
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).a) as usize - ptr as usize
+                },
+                0usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Angle),
+                    "::",
+                    stringify!(a)
+                )
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).b) as usize - ptr as usize
+                },
+                4usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Angle),
+                    "::",
+                    stringify!(b)
+                )
+            );
+        }
+        #[allow(unused_imports)]
+        use self::super::super::root;
+        extern "C" {
+            #[link_name = "\u{1}_ZN2ns3fooEv"]
+            pub fn foo() -> ::std::os::raw::c_int;
+        }
+        extern "C" {
+            #[link_name = "\u{1}_ZN2ns3barEi"]
+            pub fn bar(x: root::ns::number) -> ::std::os::raw::c_int;
+        }
+        extern "C" {
+            #[link_name = "\u{1}_ZN2ns3bazENS_5PointE"]
+            pub fn baz(point: root::ns::Point) -> ::std::os::raw::c_int;
+        }
+    }
+    #[allow(unused_imports)]
+    use self::super::root;
+    extern "C" {
+        #[link_name = "\u{1}_Z3foov"]
+        pub fn foo() -> ::std::os::raw::c_int;
+    }
+    extern "C" {
+        #[link_name = "\u{1}_Z3bari"]
+        pub fn bar(x: root::number) -> ::std::os::raw::c_int;
+    }
+    extern "C" {
+        #[link_name = "\u{1}_Z3baz5Point"]
+        pub fn baz(point: root::Point) -> ::std::os::raw::c_int;
+    }
+}
diff --git a/bindgen-tests/tests/expectations/tests/sorted-items.rs b/bindgen-tests/tests/expectations/tests/sorted-items.rs
deleted file mode 100644
index 7df7c3d7..00000000
--- a/bindgen-tests/tests/expectations/tests/sorted-items.rs
+++ /dev/null
@@ -1,82 +0,0 @@
-#![allow(
-    dead_code,
-    non_snake_case,
-    non_camel_case_types,
-    non_upper_case_globals
-)]
-
-pub type number = ::std::os::raw::c_int;
-#[repr(C)]
-#[derive(Debug, Default, Copy, Clone)]
-pub struct Point {
-    pub x: number,
-    pub y: number,
-}
-#[repr(C)]
-#[derive(Debug, Default, Copy, Clone)]
-pub struct Angle {
-    pub a: number,
-    pub b: number,
-}
-pub const NUMBER: number = 42;
-#[test]
-fn bindgen_test_layout_Point() {
-    const UNINIT: ::std::mem::MaybeUninit<Point> =
-        ::std::mem::MaybeUninit::uninit();
-    let ptr = UNINIT.as_ptr();
-    assert_eq!(
-        ::std::mem::size_of::<Point>(),
-        8usize,
-        concat!("Size of: ", stringify!(Point))
-    );
-    assert_eq!(
-        ::std::mem::align_of::<Point>(),
-        4usize,
-        concat!("Alignment of ", stringify!(Point))
-    );
-    assert_eq!(
-        unsafe { ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize },
-        0usize,
-        concat!("Offset of field: ", stringify!(Point), "::", stringify!(x))
-    );
-    assert_eq!(
-        unsafe { ::std::ptr::addr_of!((*ptr).y) as usize - ptr as usize },
-        4usize,
-        concat!("Offset of field: ", stringify!(Point), "::", stringify!(y))
-    );
-}
-#[test]
-fn bindgen_test_layout_Angle() {
-    const UNINIT: ::std::mem::MaybeUninit<Angle> =
-        ::std::mem::MaybeUninit::uninit();
-    let ptr = UNINIT.as_ptr();
-    assert_eq!(
-        ::std::mem::size_of::<Angle>(),
-        8usize,
-        concat!("Size of: ", stringify!(Angle))
-    );
-    assert_eq!(
-        ::std::mem::align_of::<Angle>(),
-        4usize,
-        concat!("Alignment of ", stringify!(Angle))
-    );
-    assert_eq!(
-        unsafe { ::std::ptr::addr_of!((*ptr).a) as usize - ptr as usize },
-        0usize,
-        concat!("Offset of field: ", stringify!(Angle), "::", stringify!(a))
-    );
-    assert_eq!(
-        unsafe { ::std::ptr::addr_of!((*ptr).b) as usize - ptr as usize },
-        4usize,
-        concat!("Offset of field: ", stringify!(Angle), "::", stringify!(b))
-    );
-}
-extern "C" {
-    pub fn foo() -> ::std::os::raw::c_int;
-}
-extern "C" {
-    pub fn bar(x: number) -> ::std::os::raw::c_int;
-}
-extern "C" {
-    pub fn baz(point: Point) -> ::std::os::raw::c_int;
-}
diff --git a/bindgen-tests/tests/expectations/tests/sorted_items.rs b/bindgen-tests/tests/expectations/tests/sorted_items.rs
new file mode 100644
index 00000000..e04e3b60
--- /dev/null
+++ b/bindgen-tests/tests/expectations/tests/sorted_items.rs
@@ -0,0 +1,220 @@
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
+pub mod root {
+    pub type number = ::std::os::raw::c_int;
+    #[repr(C)]
+    #[derive(Debug, Default, Copy, Clone)]
+    pub struct Point {
+        pub x: root::number,
+        pub y: root::number,
+    }
+    #[repr(C)]
+    #[derive(Debug, Default, Copy, Clone)]
+    pub struct Angle {
+        pub a: root::number,
+        pub b: root::number,
+    }
+    pub const NUMBER: root::number = 42;
+    #[test]
+    fn bindgen_test_layout_Point() {
+        const UNINIT: ::std::mem::MaybeUninit<Point> =
+            ::std::mem::MaybeUninit::uninit();
+        let ptr = UNINIT.as_ptr();
+        assert_eq!(
+            ::std::mem::size_of::<Point>(),
+            8usize,
+            concat!("Size of: ", stringify!(Point))
+        );
+        assert_eq!(
+            ::std::mem::align_of::<Point>(),
+            4usize,
+            concat!("Alignment of ", stringify!(Point))
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize },
+            0usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Point),
+                "::",
+                stringify!(x)
+            )
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).y) as usize - ptr as usize },
+            4usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Point),
+                "::",
+                stringify!(y)
+            )
+        );
+    }
+    #[test]
+    fn bindgen_test_layout_Angle() {
+        const UNINIT: ::std::mem::MaybeUninit<Angle> =
+            ::std::mem::MaybeUninit::uninit();
+        let ptr = UNINIT.as_ptr();
+        assert_eq!(
+            ::std::mem::size_of::<Angle>(),
+            8usize,
+            concat!("Size of: ", stringify!(Angle))
+        );
+        assert_eq!(
+            ::std::mem::align_of::<Angle>(),
+            4usize,
+            concat!("Alignment of ", stringify!(Angle))
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).a) as usize - ptr as usize },
+            0usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Angle),
+                "::",
+                stringify!(a)
+            )
+        );
+        assert_eq!(
+            unsafe { ::std::ptr::addr_of!((*ptr).b) as usize - ptr as usize },
+            4usize,
+            concat!(
+                "Offset of field: ",
+                stringify!(Angle),
+                "::",
+                stringify!(b)
+            )
+        );
+    }
+    pub mod ns {
+        pub type number = ::std::os::raw::c_int;
+        #[repr(C)]
+        #[derive(Debug, Default, Copy, Clone)]
+        pub struct Point {
+            pub x: root::ns::number,
+            pub y: root::ns::number,
+        }
+        #[repr(C)]
+        #[derive(Debug, Default, Copy, Clone)]
+        pub struct Angle {
+            pub a: root::ns::number,
+            pub b: root::ns::number,
+        }
+        pub const NUMBER: root::ns::number = 42;
+        #[test]
+        fn bindgen_test_layout_Point() {
+            const UNINIT: ::std::mem::MaybeUninit<Point> =
+                ::std::mem::MaybeUninit::uninit();
+            let ptr = UNINIT.as_ptr();
+            assert_eq!(
+                ::std::mem::size_of::<Point>(),
+                8usize,
+                concat!("Size of: ", stringify!(Point))
+            );
+            assert_eq!(
+                ::std::mem::align_of::<Point>(),
+                4usize,
+                concat!("Alignment of ", stringify!(Point))
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).x) as usize - ptr as usize
+                },
+                0usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Point),
+                    "::",
+                    stringify!(x)
+                )
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).y) as usize - ptr as usize
+                },
+                4usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Point),
+                    "::",
+                    stringify!(y)
+                )
+            );
+        }
+        #[test]
+        fn bindgen_test_layout_Angle() {
+            const UNINIT: ::std::mem::MaybeUninit<Angle> =
+                ::std::mem::MaybeUninit::uninit();
+            let ptr = UNINIT.as_ptr();
+            assert_eq!(
+                ::std::mem::size_of::<Angle>(),
+                8usize,
+                concat!("Size of: ", stringify!(Angle))
+            );
+            assert_eq!(
+                ::std::mem::align_of::<Angle>(),
+                4usize,
+                concat!("Alignment of ", stringify!(Angle))
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).a) as usize - ptr as usize
+                },
+                0usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Angle),
+                    "::",
+                    stringify!(a)
+                )
+            );
+            assert_eq!(
+                unsafe {
+                    ::std::ptr::addr_of!((*ptr).b) as usize - ptr as usize
+                },
+                4usize,
+                concat!(
+                    "Offset of field: ",
+                    stringify!(Angle),
+                    "::",
+                    stringify!(b)
+                )
+            );
+        }
+        #[allow(unused_imports)]
+        use self::super::super::root;
+        extern "C" {
+            #[link_name = "\u{1}_ZN2ns3fooEv"]
+            pub fn foo() -> ::std::os::raw::c_int;
+        }
+        extern "C" {
+            #[link_name = "\u{1}_ZN2ns3barEi"]
+            pub fn bar(x: root::ns::number) -> ::std::os::raw::c_int;
+        }
+        extern "C" {
+            #[link_name = "\u{1}_ZN2ns3bazENS_5PointE"]
+            pub fn baz(point: root::ns::Point) -> ::std::os::raw::c_int;
+        }
+    }
+    #[allow(unused_imports)]
+    use self::super::root;
+    extern "C" {
+        #[link_name = "\u{1}_Z3foov"]
+        pub fn foo() -> ::std::os::raw::c_int;
+    }
+    extern "C" {
+        #[link_name = "\u{1}_Z3bari"]
+        pub fn bar(x: root::number) -> ::std::os::raw::c_int;
+    }
+    extern "C" {
+        #[link_name = "\u{1}_Z3baz5Point"]
+        pub fn baz(point: root::Point) -> ::std::os::raw::c_int;
+    }
+}
diff --git a/bindgen-tests/tests/headers/merge-extern-blocks.h b/bindgen-tests/tests/headers/merge-extern-blocks.h
deleted file mode 100644
index 1d46b7d4..00000000
--- a/bindgen-tests/tests/headers/merge-extern-blocks.h
+++ /dev/null
@@ -1,6 +0,0 @@
-// bindgen-flags: --merge-extern-blocks -- --target=x86_64-unknown-linux
-int foo();
-typedef struct Point {
-    int x;
-} Point;
-int bar();
diff --git a/bindgen-tests/tests/headers/merge-extern-blocks.hpp b/bindgen-tests/tests/headers/merge-extern-blocks.hpp
new file mode 100644
index 00000000..392e34a3
--- /dev/null
+++ b/bindgen-tests/tests/headers/merge-extern-blocks.hpp
@@ -0,0 +1,14 @@
+// bindgen-flags: --merge-extern-blocks --enable-cxx-namespaces -- --target=x86_64-unknown-linux
+int foo();
+typedef struct Point {
+    int x;
+} Point;
+int bar();
+
+namespace ns {
+    int foo();
+    typedef struct Point {
+        int x;
+    } Point;
+    int bar();
+}
diff --git a/bindgen-tests/tests/headers/sorted-items.h b/bindgen-tests/tests/headers/sorted-items.h
deleted file mode 100644
index 11fc2ef4..00000000
--- a/bindgen-tests/tests/headers/sorted-items.h
+++ /dev/null
@@ -1,17 +0,0 @@
-// bindgen-flags: --sort-semantically -- --target=x86_64-unknown-linux
-
-int foo();
-typedef int number;
-int bar(number x);
-struct Point
-{
-    number x;
-    number y;
-};
-struct Angle
-{
-    number a;
-    number b;
-};
-int baz(struct Point point);
-const number NUMBER = 42;
diff --git a/bindgen-tests/tests/headers/sorted_items.hpp b/bindgen-tests/tests/headers/sorted_items.hpp
new file mode 100644
index 00000000..9b5ced96
--- /dev/null
+++ b/bindgen-tests/tests/headers/sorted_items.hpp
@@ -0,0 +1,35 @@
+// bindgen-flags: --sort-semantically --enable-cxx-namespaces -- --target=x86_64-unknown-linux
+
+int foo();
+typedef int number;
+int bar(number x);
+struct Point
+{
+    number x;
+    number y;
+};
+struct Angle
+{
+    number a;
+    number b;
+};
+int baz(struct Point point);
+const number NUMBER = 42;
+
+namespace ns {
+    int foo();
+    typedef int number;
+    int bar(number x);
+    struct Point
+    {
+        number x;
+        number y;
+    };
+    struct Angle
+    {
+        number a;
+        number b;
+    };
+    int baz(struct Point point);
+    const number NUMBER = 42;
+}
diff --git a/bindgen/Cargo.toml b/bindgen/Cargo.toml
index dca779bd..3965ad4d 100644
--- a/bindgen/Cargo.toml
+++ b/bindgen/Cargo.toml
@@ -45,7 +45,7 @@ lazycell = "1"
 lazy_static = "1"
 peeking_take_while = "0.1.2"
 quote = { version = "1", default-features = false }
-syn = { version = "1.0.99", features = ["full", "extra-traits"]}
+syn = { version = "1.0.99", features = ["full", "extra-traits", "visit-mut"]}
 regex = { version = "1.5", default-features = false , features = ["std", "unicode"] }
 which = { version = "4.2.1", optional = true, default-features = false }
 shlex = "1"
diff --git a/bindgen/codegen/postprocessing/merge_extern_blocks.rs b/bindgen/codegen/postprocessing/merge_extern_blocks.rs
index 2b761494..05e7e9ef 100644
--- a/bindgen/codegen/postprocessing/merge_extern_blocks.rs
+++ b/bindgen/codegen/postprocessing/merge_extern_blocks.rs
@@ -1,46 +1,66 @@
-use syn::{Item, ItemForeignMod};
+use syn::{
+    visit_mut::{visit_item_mod_mut, VisitMut},
+    Item, ItemForeignMod, ItemMod,
+};
 
-pub(super) fn merge_extern_blocks(items: &mut Vec<Item>) {
-    // Keep all the extern blocks in a different `Vec` for faster search.
-    let mut foreign_mods = Vec::<ItemForeignMod>::new();
+pub(super) fn merge_extern_blocks(item_mod: &mut ItemMod) {
+    Visitor.visit_item_mod_mut(item_mod)
+}
+
+struct Visitor;
 
-    for item in std::mem::take(items) {
-        match item {
-            Item::ForeignMod(ItemForeignMod {
-                attrs,
-                abi,
-                brace_token,
-                items: foreign_items,
-            }) => {
-                let mut exists = false;
-                for foreign_mod in &mut foreign_mods {
-                    // Check if there is a extern block with the same ABI and
-                    // attributes.
-                    if foreign_mod.attrs == attrs && foreign_mod.abi == abi {
-                        // Merge the items of the two blocks.
-                        foreign_mod.items.extend_from_slice(&foreign_items);
-                        exists = true;
-                        break;
+impl VisitMut for Visitor {
+    fn visit_item_mod_mut(&mut self, item_mod: &mut ItemMod) {
+        if let Some((_, ref mut items)) = item_mod.content {
+            // Keep all the extern blocks in a different `Vec` for faster search.
+            let mut extern_blocks = Vec::<ItemForeignMod>::new();
+
+            for item in std::mem::take(items) {
+                if let Item::ForeignMod(ItemForeignMod {
+                    attrs,
+                    abi,
+                    brace_token,
+                    items: extern_block_items,
+                }) = item
+                {
+                    let mut exists = false;
+                    for extern_block in &mut extern_blocks {
+                        // Check if there is a extern block with the same ABI and
+                        // attributes.
+                        if extern_block.attrs == attrs &&
+                            extern_block.abi == abi
+                        {
+                            // Merge the items of the two blocks.
+                            extern_block
+                                .items
+                                .extend_from_slice(&extern_block_items);
+                            exists = true;
+                            break;
+                        }
                     }
+                    // If no existing extern block had the same ABI and attributes, store
+                    // it.
+                    if !exists {
+                        extern_blocks.push(ItemForeignMod {
+                            attrs,
+                            abi,
+                            brace_token,
+                            items: extern_block_items,
+                        });
+                    }
+                } else {
+                    // If the item is not an extern block, we don't have to do anything and just
+                    // push it back.
+                    items.push(item);
                 }
-                // If no existing extern block had the same ABI and attributes, store
-                // it.
-                if !exists {
-                    foreign_mods.push(ItemForeignMod {
-                        attrs,
-                        abi,
-                        brace_token,
-                        items: foreign_items,
-                    });
-                }
             }
-            // If the item is not an extern block, we don't have to do anything.
-            _ => items.push(item),
+
+            // Move all the extern blocks alongside the rest of the items.
+            for extern_block in extern_blocks {
+                items.push(Item::ForeignMod(extern_block));
+            }
         }
-    }
 
-    // Move all the extern blocks alongside the rest of the items.
-    for foreign_mod in foreign_mods {
-        items.push(Item::ForeignMod(foreign_mod));
+        visit_item_mod_mut(self, item_mod)
     }
 }
diff --git a/bindgen/codegen/postprocessing/mod.rs b/bindgen/codegen/postprocessing/mod.rs
index c6612f2b..1d5a4983 100644
--- a/bindgen/codegen/postprocessing/mod.rs
+++ b/bindgen/codegen/postprocessing/mod.rs
@@ -1,6 +1,6 @@
 use proc_macro2::TokenStream;
 use quote::ToTokens;
-use syn::Item;
+use syn::{parse2, ItemMod};
 
 use crate::BindgenOptions;
 
@@ -12,7 +12,7 @@ use sort_semantically::sort_semantically;
 
 struct PostProcessingPass {
     should_run: fn(&BindgenOptions) -> bool,
-    run: fn(&mut Vec<Item>),
+    run: fn(&mut ItemMod),
 }
 
 // TODO: This can be a const fn when mutable references are allowed in const
@@ -21,7 +21,7 @@ macro_rules! pass {
     ($pass:ident) => {
         PostProcessingPass {
             should_run: |options| options.$pass,
-            run: |items| $pass(items),
+            run: |item_mod| $pass(item_mod),
         }
     };
 }
@@ -38,29 +38,29 @@ pub(crate) fn postprocessing(
         return items.into_iter().collect();
     }
     let module_wrapped_tokens =
-        quote!(mod wrapper_for_sorting_hack { #( #items )* });
+        quote!(mod wrapper_for_postprocessing_hack { #( #items )* });
 
     // This syn business is a hack, for now. This means that we are re-parsing already
     // generated code using `syn` (as opposed to `quote`) because `syn` provides us more
     // control over the elements.
     // One caveat is that some of the items coming from `quote`d output might have
     // multiple items within them. Hence, we have to wrap the incoming in a `mod`.
-    // The two `unwrap`s here are deliberate because
-    //      The first one won't panic because we build the `mod` and know it is there
-    //      The second one won't panic because we know original output has something in
-    //      it already.
-    let (_, mut items) = syn::parse2::<syn::ItemMod>(module_wrapped_tokens)
-        .unwrap()
-        .content
-        .unwrap();
+    // The `unwrap` here is deliberate because bindgen should generate valid rust items at all
+    // times.
+    let mut item_mod = parse2::<ItemMod>(module_wrapped_tokens).unwrap();
 
     for pass in PASSES {
         if (pass.should_run)(options) {
-            (pass.run)(&mut items);
+            (pass.run)(&mut item_mod);
         }
     }
 
-    let synful_items = items.into_iter().map(|item| item.into_token_stream());
+    let synful_items = item_mod
+        .content
+        .map(|(_, items)| items)
+        .unwrap_or_default()
+        .into_iter()
+        .map(|item| item.into_token_stream());
 
     quote! { #( #synful_items )* }
 }
diff --git a/bindgen/codegen/postprocessing/sort_semantically.rs b/bindgen/codegen/postprocessing/sort_semantically.rs
index 96596cb0..4f23ab73 100644
--- a/bindgen/codegen/postprocessing/sort_semantically.rs
+++ b/bindgen/codegen/postprocessing/sort_semantically.rs
@@ -1,24 +1,38 @@
-use syn::Item;
+use syn::{
+    visit_mut::{visit_item_mod_mut, VisitMut},
+    Item, ItemMod,
+};
 
-pub(super) fn sort_semantically(items: &mut [Item]) {
-    items.sort_by_key(|item| match item {
-        Item::Type(_) => 0,
-        Item::Struct(_) => 1,
-        Item::Const(_) => 2,
-        Item::Fn(_) => 3,
-        Item::Enum(_) => 4,
-        Item::Union(_) => 5,
-        Item::Static(_) => 6,
-        Item::Trait(_) => 7,
-        Item::TraitAlias(_) => 8,
-        Item::Impl(_) => 9,
-        Item::Mod(_) => 10,
-        Item::Use(_) => 11,
-        Item::Verbatim(_) => 12,
-        Item::ExternCrate(_) => 13,
-        Item::ForeignMod(_) => 14,
-        Item::Macro(_) => 15,
-        Item::Macro2(_) => 16,
-        _ => 18,
-    });
+pub(super) fn sort_semantically(item_mod: &mut ItemMod) {
+    Visitor.visit_item_mod_mut(item_mod)
+}
+
+struct Visitor;
+
+impl VisitMut for Visitor {
+    fn visit_item_mod_mut(&mut self, item_mod: &mut ItemMod) {
+        if let Some((_, ref mut items)) = item_mod.content {
+            items.sort_by_key(|item| match item {
+                Item::Type(_) => 0,
+                Item::Struct(_) => 1,
+                Item::Const(_) => 2,
+                Item::Fn(_) => 3,
+                Item::Enum(_) => 4,
+                Item::Union(_) => 5,
+                Item::Static(_) => 6,
+                Item::Trait(_) => 7,
+                Item::TraitAlias(_) => 8,
+                Item::Impl(_) => 9,
+                Item::Mod(_) => 10,
+                Item::Use(_) => 11,
+                Item::Verbatim(_) => 12,
+                Item::ExternCrate(_) => 13,
+                Item::ForeignMod(_) => 14,
+                Item::Macro(_) => 15,
+                Item::Macro2(_) => 16,
+                _ => 18,
+            });
+        }
+        visit_item_mod_mut(self, item_mod)
+    }
 }