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.

3 files changed, 107 insertions, 73 deletions

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)
+    }
 }