Add option to deduplicate impl blocks

bindgen-tests/tests/headers/merge_impl_blocks.hpp

@@ -0,0 +1,20 @@
+// bindgen-flags: --merge-impl-blocks --newtype-enum '.*' --enable-cxx-namespaces -- --target=x86_64-unknown-linux
+int foo();
+enum Foo {
+  Bar = 1 << 1,
+  Baz = 1 << 2,
+  Duplicated = 1 << 2,
+  Negative = -3,
+};
+int bar();
+
+namespace ns {
+    int foo();
+    enum Bar {
+      B0 = 1,
+      B1 = B0 + 3,
+      B2 = B0 + 2,
+      B3 = B0 - 2,
+    };
+    int bar();
+}

bindgen/codegen/postprocessing/merge_impl_blocks.rs

@@ -0,0 +1,82 @@
+use syn::{
+    visit_mut::{visit_file_mut, visit_item_mod_mut, VisitMut},
+    File, Item, ItemImpl, ItemMod,
+};
+
+pub(super) fn merge_impl_blocks(file: &mut File) {
+    Visitor.visit_file_mut(file);
+}
+
+struct Visitor;
+
+impl VisitMut for Visitor {
+    fn visit_file_mut(&mut self, file: &mut File) {
+        visit_items(&mut file.items);
+        visit_file_mut(self, file);
+    }
+
+    fn visit_item_mod_mut(&mut self, item_mod: &mut ItemMod) {
+        if let Some((_, ref mut items)) = item_mod.content {
+            visit_items(items);
+        }
+        visit_item_mod_mut(self, item_mod);
+    }
+}
+
+fn visit_items(items: &mut Vec<Item>) {
+    // Keep all the impl blocks in a different `Vec` for faster search.
+    let mut impl_blocks = Vec::<ItemImpl>::new();
+
+    for item in std::mem::take(items) {
+        if let Item::Impl(ItemImpl {
+            attrs,
+            defaultness,
+            unsafety,
+            impl_token,
+            generics,
+            trait_: None, // don't merge `impl <Trait> for T` blocks
+            self_ty,
+            brace_token,
+            items: impl_block_items,
+        }) = item
+        {
+            let mut exists = false;
+            for impl_block in &mut impl_blocks {
+                // Check if there is an equivalent impl block
+                if impl_block.attrs == attrs &&
+                    impl_block.unsafety == unsafety &&
+                    impl_block.generics == generics &&
+                    impl_block.self_ty == self_ty
+                {
+                    // Merge the items of the two blocks.
+                    impl_block.items.extend_from_slice(&impl_block_items);
+                    exists = true;
+                    break;
+                }
+            }
+            // If no matching impl block was found, store it.
+            if !exists {
+                impl_blocks.push(ItemImpl {
+                    attrs,
+                    defaultness,
+                    unsafety,
+                    impl_token,
+                    generics,
+                    trait_: None,
+                    self_ty,
+                    brace_token,
+                    items: impl_block_items,
+                });
+            }
+        } else {
+            // If the item is not an mergeable impl block, we don't have to do
+            // anything and just push it back.
+            items.push(item);
+        }
+    }
+
+    // Move all the impl blocks alongside the rest of the items.
+    for impl_block in impl_blocks {
+        items.push(Item::Impl(impl_block));
+    }
+}

bindgen/codegen/postprocessing/mod.rs

@@ -5,9 +5,11 @@ use syn::{parse2, File};
 use crate::BindgenOptions;
 
 mod merge_extern_blocks;
+mod merge_impl_blocks;
 mod sort_semantically;
 
 use merge_extern_blocks::merge_extern_blocks;
+use merge_impl_blocks::merge_impl_blocks;
 use sort_semantically::sort_semantically;
 
 struct PostProcessingPass {
@@ -26,8 +28,11 @@ macro_rules! pass {
     };
 }
 
-const PASSES: &[PostProcessingPass] =
-    &[pass!(merge_extern_blocks), pass!(sort_semantically)];
+const PASSES: &[PostProcessingPass] = &[
+    pass!(merge_extern_blocks),
+    pass!(merge_impl_blocks),
+    pass!(sort_semantically),
+];
 
 pub(crate) fn postprocessing(
     items: Vec<TokenStream>,

bindgen/options/cli.rs

@@ -456,6 +456,9 @@ struct BindgenCommand {
     /// Deduplicates extern blocks.
     #[arg(long)]
     merge_extern_blocks: bool,
+    /// Deduplicates `impl` blocks.
+    #[arg(long)]
+    merge_impl_blocks: bool,
     /// Overrides the ABI of functions matching REGEX. The OVERRIDE value must be of the shape REGEX=ABI where ABI can be one of C, stdcall, efiapi, fastcall, thiscall, aapcs, win64 or C-unwind<.>
     #[arg(long, value_name = "OVERRIDE", value_parser = parse_abi_override)]
     override_abi: Vec<(Abi, String)>,
@@ -640,6 +643,7 @@ where
         vtable_generation,
         sort_semantically,
         merge_extern_blocks,
+        merge_impl_blocks,
         override_abi,
         wrap_unsafe_ops,
         clang_macro_fallback,
@@ -939,6 +943,7 @@ where
             vtable_generation,
             sort_semantically,
             merge_extern_blocks,
+            merge_impl_blocks,
             override_abi => |b, (abi, regex)| b.override_abi(abi, regex),
             wrap_unsafe_ops,
             clang_macro_fallback => |b, _| b.clang_macro_fallback(),

bindgen/options/mod.rs

@@ -2030,6 +2030,19 @@ options! {
         },
         as_args: "--merge-extern-blocks",
     },
+    /// Whether to deduplicate `impl` blocks.
+    merge_impl_blocks: bool {
+        methods: {
+            /// Merge all `impl` blocks under the same module into a single one.
+            ///
+            /// `impl` blocks are not merged by default.
+            pub fn merge_impl_blocks(mut self, doit: bool) -> Self {
+                self.options.merge_impl_blocks = doit;
+                self
+            }
+        },
+        as_args: "--merge-impl-blocks",
+    },
     /// Whether to wrap unsafe operations in unsafe blocks.
     wrap_unsafe_ops: bool {
         methods: {