Auto merge of #689 - fitzgen:Kowasaki-master, r=fitzgen

Emit `PhantomData<UnsafeCell<T>>` members for all generic parameters

This makes generated generic structs lifetime invariant, since we cannot know
the C++ type's true variance.

Fixes #506

Rebased + squashed version of #635; cc @Kowasaki

To resolve the conflicts and rebase and squash, I did essentially these commands:

```
$ git fetch servo
$ git checkout -b Kowasaki-master servo/master
$ git merge --squash --edit Kowasaki/master
$ cargo test
$ cd tests/expectations
$ cargo test
$ cd -
$ git commit --author="Kowasaki"
$ git push fitzgen Kowasaki-master
```

Hopefully that is useful for you in the future :) Thanks for fixing this issue!

Author: bors-servo

src/codegen/mod.rs

@@ -1465,11 +1465,20 @@ impl CodeGenerator for CompInfo {
         let mut generics = aster::AstBuilder::new().generics();
 
         if let Some(ref params) = used_template_params {
-            for ty in params.iter() {
+            for (idx, ty) in params.iter().enumerate() {
                 let param = ctx.resolve_type(*ty);
                 let name = param.name().unwrap();
                 let ident = ctx.rust_ident(name);
+
                 generics = generics.ty_param_id(ident);
+
+                let prefix = ctx.trait_prefix();
+                let phantom_ty = quote_ty!(
+                    ctx.ext_cx(),
+                    ::$prefix::marker::PhantomData<::$prefix::cell::UnsafeCell<$ident>>);
+                let phantom_field = StructFieldBuilder::named(format!("_phantom_{}", idx))
+                    .build_ty(phantom_ty);
+                fields.push(phantom_field);
             }
         }
 

tests/expectations/tests/anonymous-template-types.rs

@@ -8,6 +8,7 @@
 #[derive(Debug, Copy, Clone)]
 pub struct Foo<T> {
     pub t_member: T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for Foo<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }
@@ -21,6 +22,7 @@ pub struct Bar {
 #[derive(Debug, Copy, Clone)]
 pub struct Quux<V> {
     pub v_member: V,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<V>>,
 }
 impl <V> Default for Quux<V> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/class_nested.rs

@@ -53,6 +53,7 @@ impl Clone for A_C {
 #[derive(Debug, Copy, Clone)]
 pub struct A_D<T> {
     pub foo: T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for A_D<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }
@@ -115,11 +116,13 @@ impl Clone for D {
 #[derive(Debug, Copy, Clone)]
 pub struct Templated<T> {
     pub member: T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 #[repr(C)]
 #[derive(Debug, Copy, Clone)]
 pub struct Templated_Templated_inner<T> {
     pub member_ptr: *mut T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for Templated_Templated_inner<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/class_with_dtor.rs

@@ -8,6 +8,7 @@
 #[derive(Debug)]
 pub struct HandleWithDtor<T> {
     pub ptr: *mut T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for HandleWithDtor<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/const_tparam.rs

@@ -9,6 +9,7 @@
 pub struct C<T> {
     pub foo: *const T,
     pub bar: *mut T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for C<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/default-template-parameter.rs

@@ -9,6 +9,8 @@
 pub struct Foo<T, U> {
     pub t: T,
     pub u: U,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
+    _phantom_1: ::std::marker::PhantomData<::std::cell::UnsafeCell<U>>,
 }
 impl <T, U> Default for Foo<T, U> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/forward-declaration-autoptr.rs

@@ -13,6 +13,7 @@ pub struct Foo {
 #[derive(Debug, Copy, Clone)]
 pub struct RefPtr<T> {
     pub m_inner: *mut T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for RefPtr<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/forward-inherit-struct-with-fields.rs

@@ -8,6 +8,7 @@
 #[derive(Debug, Copy, Clone)]
 pub struct Rooted<T> {
     pub _base: js_RootedBase<T>,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for Rooted<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }
@@ -17,6 +18,7 @@ impl <T> Default for Rooted<T> {
 pub struct js_RootedBase<T> {
     pub foo: *mut T,
     pub next: *mut Rooted<T>,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for js_RootedBase<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/inherit_named.rs

@@ -13,6 +13,7 @@ pub struct Wohoo {
 #[derive(Debug, Copy, Clone)]
 pub struct Weeee<T> {
     pub _base: T,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 impl <T> Default for Weeee<T> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }

tests/expectations/tests/issue-584-stylo-template-analysis-panic.rs

@@ -43,6 +43,7 @@ impl Clone for A {
 #[derive(Debug, Copy, Clone)]
 pub struct e<c> {
     pub d: RefPtr<c>,
+    _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<c>>,
 }
 impl <c> Default for e<c> {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }