Improve error message for #[repr(packed(N))]

pin-project-internal/src/pin_project/attribute.rs

@@ -338,14 +338,21 @@ fn ensure_not_packed(item: &ItemStruct) -> Result<TokenStream> {
     for meta in item.attrs.iter().filter_map(|attr| attr.parse_meta().ok()) {
         if let Meta::List(l) = meta {
             if l.path.is_ident("repr") {
-                for repr in &l.nested {
-                    if let NestedMeta::Meta(Meta::Path(p)) = repr {
-                        if p.is_ident("packed") {
+                for repr in l.nested.iter() {
+                    match repr {
+                        NestedMeta::Meta(Meta::Path(p)) if p.is_ident("packed") => {
                             return Err(error!(
                                 p,
                                 "#[pin_project] attribute may not be used on #[repr(packed)] types"
                             ));
                         }
+                        NestedMeta::Meta(Meta::List(l)) if l.path.is_ident("packed") => {
+                            return Err(error!(
+                                l,
+                                "#[pin_project] attribute may not be used on #[repr(packed(N))] types"
+                            ));
+                        }
+                        _ => {}
                     }
                 }
             }
@@ -394,7 +401,8 @@ fn ensure_not_packed(item: &ItemStruct) -> Result<TokenStream> {
             for Field { attrs, ident, .. } in named {
                 let cfg = collect_cfg(attrs);
                 field_refs.push(quote! {
-                    #(#cfg)* { &val.#ident; }
+                    #(#cfg)*
+                    { &val.#ident; }
                 });
             }
         }

tests/repr_packed.rs

@@ -1,6 +1,7 @@
 #![warn(unsafe_code)]
 #![warn(rust_2018_idioms, single_use_lifetimes)]
 #![allow(dead_code)]
+#![deny(safe_packed_borrows)]
 
 use std::cell::Cell;
 

tests/ui/cfg/auxiliary/sneaky_macro.rs

@@ -65,3 +65,13 @@ pub fn add_pinned_field(_: TokenStream, input: TokenStream) -> TokenStream {
 pub fn hidden_repr(attr: TokenStream, item: TokenStream) -> TokenStream {
     format!("#[repr({})] {}", attr, item).parse().unwrap()
 }
+
+#[proc_macro_attribute]
+pub fn hidden_repr_cfg_any(attr: TokenStream, item: TokenStream) -> TokenStream {
+    format!("#[cfg_attr(any(), repr({}))] {}", attr, item).parse().unwrap()
+}
+
+#[proc_macro_attribute]
+pub fn hidden_repr_cfg_not_any(attr: TokenStream, item: TokenStream) -> TokenStream {
+    format!("#[cfg_attr(not(any()), repr({}))] {}", attr, item).parse().unwrap()
+}

tests/ui/cfg/packed_sneaky.stderr → tests/ui/cfg/packed_sneaky-1.stderr

@@ -1,11 +1,11 @@
 error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
-  --> $DIR/packed_sneaky.rs:20:1
+  --> $DIR/packed_sneaky-1.rs:20:1
    |
 20 | #[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
    | ^^^^^^^^^^^^^^
    |
 note: lint level defined here
-  --> $DIR/packed_sneaky.rs:20:1
+  --> $DIR/packed_sneaky-1.rs:20:1
    |
 20 | #[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
    | ^^^^^^^^^^^^^^

tests/ui/cfg/packed_sneaky-2.rs

@@ -0,0 +1,17 @@
+// run-pass
+// aux-build:sneaky_macro.rs
+
+#[macro_use]
+extern crate sneaky_macro;
+
+use pin_project::pin_project;
+
+// #[cfg_attr(any(), repr(packed))]
+#[pin_project]
+#[hidden_repr_cfg_any(packed)]
+struct Foo {
+    #[pin]
+    field: u32,
+}
+
+fn main() {}

tests/ui/pin_project/packed_sneaky.rs → tests/ui/cfg/packed_sneaky-3.rs

@@ -6,8 +6,9 @@ extern crate sneaky_macro;
 
 use pin_project::pin_project;
 
+// #[cfg_attr(not(any()), repr(packed))]
 #[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
-#[hidden_repr(packed)]
+#[hidden_repr_cfg_not_any(packed)]
 struct Foo {
     #[pin]
     field: u32,

tests/ui/cfg/packed_sneaky-3.stderr

@@ -0,0 +1,17 @@
+error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
+  --> $DIR/packed_sneaky-3.rs:10:1
+   |
+10 | #[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/packed_sneaky-3.rs:10:1
+   |
+10 | #[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
+   = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior
+
+error: aborting due to previous error
+

tests/ui/pin_project/auxiliary/sneaky_macro.rs

@@ -1,4 +1,4 @@
-// force-host 
+// force-host
 // no-prefer-dynamic
 
 #![crate_type = "proc-macro"]
@@ -12,3 +12,7 @@ pub fn hidden_repr(attr: TokenStream, item: TokenStream) -> TokenStream {
     format!("#[repr({})] {}", attr, item).parse().unwrap()
 }
 
+#[proc_macro]
+pub fn hidden_repr_macro(item: TokenStream) -> TokenStream {
+    format!("#[repr(packed)] {}", item).parse().unwrap()
+}

tests/ui/pin_project/packed.rs

@@ -3,18 +3,25 @@
 use pin_project::pin_project;
 
 #[pin_project]
-#[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] type
-struct Foo {
+#[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] types
+struct A {
     #[pin]
     field: u8,
 }
 
 // Test putting 'repr' before the 'pin_project' attribute
-#[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] type
+#[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] types
 #[pin_project]
-struct Foo2 {
+struct B {
     #[pin]
     field: u8,
 }
 
+#[pin_project]
+#[repr(packed(2))] //~ ERROR may not be used on #[repr(packed(N))] types
+struct C {
+    #[pin]
+    field: u32,
+}
+
 fn main() {}

tests/ui/pin_project/packed.stderr

@@ -1,14 +1,20 @@
 error: #[pin_project] attribute may not be used on #[repr(packed)] types
  --> $DIR/packed.rs:6:8
   |
-6 | #[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] type
+6 | #[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] types
   |        ^^^^^^
 
 error: #[pin_project] attribute may not be used on #[repr(packed)] types
   --> $DIR/packed.rs:13:8
    |
-13 | #[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] type
+13 | #[repr(packed, C)] //~ ERROR may not be used on #[repr(packed)] types
    |        ^^^^^^
 
-error: aborting due to 2 previous errors
+error: #[pin_project] attribute may not be used on #[repr(packed(N))] types
+  --> $DIR/packed.rs:21:8
+   |
+21 | #[repr(packed(2))] //~ ERROR may not be used on #[repr(packed(N))] types
+   |        ^^^^^^^^^
+
+error: aborting due to 3 previous errors
 

tests/ui/pin_project/packed_sneaky-1.rs

@@ -0,0 +1,36 @@
+// compile-fail
+// aux-build:sneaky_macro.rs
+
+#[macro_use]
+extern crate sneaky_macro;
+
+use pin_project::{pin_project, pinned_drop, UnsafeUnpin};
+use std::pin::Pin;
+
+#[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+#[hidden_repr(packed)]
+struct A {
+    #[pin]
+    field: u32,
+}
+
+#[pin_project(UnsafeUnpin)] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+#[hidden_repr(packed)]
+struct C {
+    #[pin]
+    field: u32,
+}
+
+unsafe impl UnsafeUnpin for C {}
+
+#[pin_project(PinnedDrop)] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+#[hidden_repr(packed)]
+struct D {
+    #[pin]
+    field: u32,
+}
+
+#[pinned_drop]
+fn drop_d(_: Pin<&mut D>) {}
+
+fn main() {}

tests/ui/pin_project/packed_sneaky-1.stderr

@@ -0,0 +1,47 @@
+error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
+  --> $DIR/packed_sneaky-1.rs:10:1
+   |
+10 | #[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/packed_sneaky-1.rs:10:1
+   |
+10 | #[pin_project] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
+   = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior
+
+error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
+  --> $DIR/packed_sneaky-1.rs:17:1
+   |
+17 | #[pin_project(UnsafeUnpin)] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/packed_sneaky-1.rs:17:1
+   |
+17 | #[pin_project(UnsafeUnpin)] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
+   = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior
+
+error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
+  --> $DIR/packed_sneaky-1.rs:26:1
+   |
+26 | #[pin_project(PinnedDrop)] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/packed_sneaky-1.rs:26:1
+   |
+26 | #[pin_project(PinnedDrop)] //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
+   = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior
+
+error: aborting due to 3 previous errors
+

tests/ui/pin_project/packed_sneaky-2.rs

@@ -0,0 +1,17 @@
+// compile-fail
+// aux-build:sneaky_macro.rs
+
+#[macro_use]
+extern crate sneaky_macro;
+
+use pin_project::pin_project;
+
+hidden_repr_macro! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+    #[pin_project]
+    struct B {
+        #[pin]
+        field: u32,
+    }
+}
+
+fn main() {}

tests/ui/pin_project/packed_sneaky-2.stderr

@@ -0,0 +1,16 @@
+error: #[pin_project] attribute may not be used on #[repr(packed)] types
+  --> $DIR/packed_sneaky-2.rs:9:1
+   |
+9  | / hidden_repr_macro! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+10 | |     #[pin_project]
+11 | |     struct B {
+12 | |         #[pin]
+13 | |         field: u32,
+14 | |     }
+15 | | }
+   | | ^ in this macro invocation
+   | |_|
+   | 
+
+error: aborting due to previous error
+

tests/ui/pin_project/safe_packed_borrows.rs

@@ -0,0 +1,25 @@
+// compile-fail
+
+#![deny(safe_packed_borrows)]
+
+// Refs: https://github.com/rust-lang/rust/issues/46043
+
+#[repr(packed)]
+struct A {
+    field: u32,
+}
+
+#[repr(packed(2))]
+struct B {
+    field: u32,
+}
+
+fn foo() {
+    let a = A { field: 1 };
+    &a.field; //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+
+    let b = B { field: 1 };
+    &b.field; //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+}
+
+fn main() {}

tests/ui/pin_project/safe_packed_borrows.stderr

@@ -0,0 +1,27 @@
+error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
+  --> $DIR/safe_packed_borrows.rs:17:5
+   |
+17 |     &a.field; //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   |     ^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/safe_packed_borrows.rs:1:9
+   |
+1  | #![deny(safe_packed_borrows)]
+   |         ^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
+   = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior
+
+error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
+  --> $DIR/safe_packed_borrows.rs:20:5
+   |
+20 |     &b.field; //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+   |     ^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
+   = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior
+
+error: aborting due to 2 previous errors
+