Auto merge of #1241 - emilio:fwd-decl-no-fun, r=fitzgen

codegen: Make forward declarations go through the more generic path.

Instead of special-casing.

This allows to use the normal flags to control what can be or not derived for
them.

Arguably deriving Copy / Clone is kind of busted for those, but changing this by
default broke tests (RefPtr<ForwardDeclaredType> stopped working for example).

So I think this is a good compromise.

Fixes #1238

7 files changed, 52 insertions, 45 deletions

diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index f9e5e77c..0ddcdc0a 100644
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -1425,23 +1425,6 @@ impl CodeGenerator for CompInfo {
         let layout = ty.layout(ctx);
         let mut packed = self.is_packed(ctx, &layout);
 
-        // generate tuple struct if struct or union is a forward declaration,
-        // skip for now if template parameters are needed.
-        //
-        // NB: We generate a proper struct to avoid struct/function name
-        // collisions.
-        if self.is_forward_declaration() && used_template_params.is_none() {
-            let struct_name = item.canonical_name(ctx);
-            let struct_name = ctx.rust_ident_raw(struct_name);
-            let tuple_struct = quote! {
-                #[repr(C)]
-                #[derive(Debug, Copy, Clone)]
-                pub struct #struct_name { _unused: [u8; 0] }
-            };
-            result.push(tuple_struct);
-            return;
-        }
-
         let canonical_name = item.canonical_name(ctx);
         let canonical_ident = ctx.rust_ident(&canonical_name);
 
@@ -1497,14 +1480,6 @@ impl CodeGenerator for CompInfo {
             }
         }
 
-        let is_union = self.kind() == CompKind::Union;
-        if is_union {
-            result.saw_union();
-            if !self.can_be_rust_union(ctx) {
-                result.saw_bindgen_union();
-            }
-        }
-
         let mut methods = vec![];
         if !is_opaque {
             let codegen_depth = item.codegen_depth(ctx);
@@ -1529,8 +1504,14 @@ impl CodeGenerator for CompInfo {
             }
         }
 
+        let is_union = self.kind() == CompKind::Union;
         let layout = item.kind().expect_type().layout(ctx);
-        if is_union && !is_opaque {
+        if is_union && !is_opaque && !self.is_forward_declaration() {
+            result.saw_union();
+            if !self.can_be_rust_union(ctx) {
+                result.saw_bindgen_union();
+            }
+
             let layout = layout.expect("Unable to get layout information?");
             let ty = helpers::blob(layout);
 
@@ -1594,7 +1575,11 @@ impl CodeGenerator for CompInfo {
         //
         // NOTE: This check is conveniently here to avoid the dummy fields we
         // may add for unused template parameters.
-        if item.is_zero_sized(ctx) {
+        if self.is_forward_declaration() {
+            fields.push(quote! {
+                _unused: [u8; 0],
+            });
+        } else if item.is_zero_sized(ctx) {
             let has_address = if is_opaque {
                 // Generate the address field if it's an opaque type and
                 // couldn't determine the layout of the blob.
@@ -1664,12 +1649,11 @@ impl CodeGenerator for CompInfo {
         if item.can_derive_default(ctx) {
             derives.push("Default");
         } else {
-            needs_default_impl = ctx.options().derive_default;
+            needs_default_impl =
+                ctx.options().derive_default && !self.is_forward_declaration();
         }
 
-        if item.can_derive_copy(ctx) && !item.annotations().disallow_copy() &&
-            ctx.options().derive_copy
-        {
+        if item.can_derive_copy(ctx) && !item.annotations().disallow_copy() {
             derives.push("Copy");
 
             if ctx.options().rust_features().builtin_clone_impls() ||
@@ -1762,7 +1746,7 @@ impl CodeGenerator for CompInfo {
                 }
             }
 
-            if ctx.options().layout_tests {
+            if ctx.options().layout_tests && !self.is_forward_declaration() {
                 if let Some(layout) = layout {
                     let fn_name =
                         format!("bindgen_test_layout_{}", canonical_ident.as_str());
diff --git a/src/ir/analysis/derive_copy.rs b/src/ir/analysis/derive_copy.rs
index 8da47a7f..94d457d5 100644
--- a/src/ir/analysis/derive_copy.rs
+++ b/src/ir/analysis/derive_copy.rs
@@ -235,9 +235,10 @@ impl<'ctx> MonotoneFramework for CannotDeriveCopy<'ctx> {
 
                 if info.kind() == CompKind::Union {
                     if !self.ctx.options().rust_features().untagged_union() {
-                        // NOTE: If there's no template parameters we can derive copy
-                        // unconditionally, since arrays are magical for rustc, and
-                        // __BindgenUnionField always implements copy.
+                        // NOTE: If there's no template parameters we can derive
+                        // copy unconditionally, since arrays are magical for
+                        // rustc, and __BindgenUnionField always implements
+                        // copy.
                         trace!(
                             "    comp can always derive debug if it's a Union and no template parameters"
                         );
diff --git a/src/ir/analysis/derive_default.rs b/src/ir/analysis/derive_default.rs
index f8f02df7..2c79a437 100644
--- a/src/ir/analysis/derive_default.rs
+++ b/src/ir/analysis/derive_default.rs
@@ -265,6 +265,11 @@ impl<'ctx> MonotoneFramework for CannotDeriveDefault<'ctx> {
                     "The early ty.is_opaque check should have handled this case"
                 );
 
+                if info.is_forward_declaration() {
+                    trace!("    cannot derive Default for forward decls");
+                    return self.insert(id);
+                }
+
                 if info.kind() == CompKind::Union {
                     if self.ctx.options().rust_features().untagged_union() {
                         trace!("    cannot derive Default for Rust unions");
diff --git a/src/ir/analysis/derive_hash.rs b/src/ir/analysis/derive_hash.rs
index 46790232..3fc31b39 100644
--- a/src/ir/analysis/derive_hash.rs
+++ b/src/ir/analysis/derive_hash.rs
@@ -251,6 +251,11 @@ impl<'ctx> MonotoneFramework for CannotDeriveHash<'ctx> {
                     "The early ty.is_opaque check should have handled this case"
                 );
 
+                if info.is_forward_declaration() {
+                    trace!("    cannot derive Hash for forward decls");
+                    return self.insert(id);
+                }
+
                 if info.kind() == CompKind::Union {
                     if self.ctx.options().rust_features().untagged_union() {
                         trace!("    cannot derive Hash for Rust unions");
diff --git a/src/ir/analysis/derive_partialeq_or_partialord.rs b/src/ir/analysis/derive_partialeq_or_partialord.rs
index 92861341..2641d2b3 100644
--- a/src/ir/analysis/derive_partialeq_or_partialord.rs
+++ b/src/ir/analysis/derive_partialeq_or_partialord.rs
@@ -236,6 +236,11 @@ impl<'ctx> CannotDerivePartialEqOrPartialOrd<'ctx> {
                     "The early ty.is_opaque check should have handled this case"
                 );
 
+                if info.is_forward_declaration() {
+                    trace!("    cannot derive for forward decls");
+                    return CanDerive::No;
+                }
+
                 if info.kind() == CompKind::Union {
                     if self.ctx.options().rust_features().untagged_union() {
                         trace!(
diff --git a/src/ir/comp.rs b/src/ir/comp.rs
index 5008dcfd..50d0ddb1 100644
--- a/src/ir/comp.rs
+++ b/src/ir/comp.rs
@@ -1543,13 +1543,20 @@ impl CompInfo {
     ///     1. Current RustTarget allows for `untagged_union`
     ///     2. Each field can derive `Copy`
     pub fn can_be_rust_union(&self, ctx: &BindgenContext) -> bool {
-        ctx.options().rust_features().untagged_union() &&
-            self.fields().iter().all(|f| match *f {
-                Field::DataMember(ref field_data) => {
-                    field_data.ty().can_derive_copy(ctx)
-                }
-                Field::Bitfields(_) => true,
-            })
+        if !ctx.options().rust_features().untagged_union() {
+            return false;
+        }
+
+        if self.is_forward_declaration() {
+            return false;
+        }
+
+        self.fields().iter().all(|f| match *f {
+            Field::DataMember(ref field_data) => {
+                field_data.ty().can_derive_copy(ctx)
+            }
+            Field::Bitfields(_) => true,
+        })
     }
 }
 
diff --git a/src/ir/context.rs b/src/ir/context.rs
index cddbeb2d..21801c9f 100644
--- a/src/ir/context.rs
+++ b/src/ir/context.rs
@@ -222,8 +222,7 @@ where
     T: Copy + Into<ItemId>
 {
     fn can_derive_default(&self, ctx: &BindgenContext) -> bool {
-        ctx.options().derive_default &&
-            ctx.lookup_can_derive_default(*self)
+        ctx.options().derive_default && ctx.lookup_can_derive_default(*self)
     }
 }
 
@@ -232,7 +231,7 @@ where
     T: Copy + Into<ItemId>
 {
     fn can_derive_copy(&self, ctx: &BindgenContext) -> bool {
-        ctx.lookup_can_derive_copy(*self)
+        ctx.options().derive_copy && ctx.lookup_can_derive_copy(*self)
     }
 }
 
@@ -2452,6 +2451,7 @@ impl BindgenContext {
         // Look up the computed value for whether the item with `id` can
         // derive `Copy` or not.
         let id = id.into();
+
         !self.lookup_has_type_param_in_array(id) &&
             !self.cannot_derive_copy.as_ref().unwrap().contains(&id)
     }