Prevent other proc macros from adding fields after the #[pin_project]…

… attribute is applied

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

@@ -70,8 +70,8 @@ fn variants(cx: &mut Context, item: &mut ItemEnum) -> Result<(Vec<TokenStream>,
     let mut proj_arms = Vec::with_capacity(item.variants.len());
     for Variant { attrs, fields, ident, .. } in &mut item.variants {
         let (proj_pat, proj_body, proj_fields) = match fields {
-            Fields::Unnamed(fields) => unnamed(cx, fields)?,
             Fields::Named(fields) => named(cx, fields)?,
+            Fields::Unnamed(fields) => unnamed(cx, fields, false)?,
             Fields::Unit => (TokenStream::new(), TokenStream::new(), TokenStream::new()),
         };
         let cfg = collect_cfg(attrs);
@@ -89,7 +89,7 @@ fn variants(cx: &mut Context, item: &mut ItemEnum) -> Result<(Vec<TokenStream>,
     Ok((proj_variants, proj_arms))
 }
 
-fn named(
+pub(super) fn named(
     cx: &mut Context,
     FieldsNamed { named: fields, .. }: &mut FieldsNamed,
 ) -> Result<(TokenStream, TokenStream, TokenStream)> {
@@ -126,9 +126,10 @@ fn named(
     Ok((proj_pat, proj_body, proj_fields))
 }
 
-fn unnamed(
+pub(super) fn unnamed(
     cx: &mut Context,
     FieldsUnnamed { unnamed: fields, .. }: &mut FieldsUnnamed,
+    is_struct: bool,
 ) -> Result<(TokenStream, TokenStream, TokenStream)> {
     let mut proj_pat = Vec::with_capacity(fields.len());
     let mut proj_body = Vec::with_capacity(fields.len());
@@ -139,7 +140,8 @@ fn unnamed(
         if !cfg.is_empty() {
             return Err(error!(
                 cfg.first(),
-                "`cfg` attributes on the field of tuple variants are not supported"
+                "`cfg` attributes on the field of tuple {} are not supported",
+                if is_struct { "structs" } else { "variants" }
             ));
         }
         if cx.find_pin_attr(attrs)? {
@@ -166,6 +168,7 @@ fn unnamed(
 
     let proj_pat = quote!((#(#proj_pat),*));
     let proj_body = quote!((#(#proj_body),*));
-    let proj_fields = quote!((#(#proj_fields),*));
+    let proj_fields =
+        if is_struct { quote!((#(#proj_fields),*);) } else { quote!((#(#proj_fields),*)) };
     Ok((proj_pat, proj_body, proj_fields))
 }

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

@@ -1,8 +1,6 @@
 use proc_macro2::TokenStream;
 use quote::{quote, ToTokens};
-use syn::{Field, Fields, FieldsNamed, FieldsUnnamed, Ident, Index, ItemStruct, Result};
-
-use crate::utils::collect_cfg;
+use syn::{Fields, FieldsNamed, FieldsUnnamed, Ident, ItemStruct, Result};
 
 use super::Context;
 
@@ -27,13 +25,13 @@ pub(super) fn validate(ident: &Ident, fields: &Fields) -> Result<()> {
 pub(super) fn parse(cx: &mut Context, mut item: ItemStruct) -> Result<TokenStream> {
     validate(&item.ident, &item.fields)?;
 
-    let (proj_fields, proj_init) = match &mut item.fields {
-        Fields::Named(fields) => named(cx, fields)?,
-        Fields::Unnamed(fields) => unnamed(cx, fields)?,
+    let (proj_pat, proj_body, proj_fields) = match &mut item.fields {
+        Fields::Named(fields) => super::enums::named(cx, fields)?,
+        Fields::Unnamed(fields) => super::enums::unnamed(cx, fields, true)?,
         Fields::Unit => unreachable!(),
     };
 
-    let proj_ident = &cx.proj_ident;
+    let Context { orig_ident, proj_ident, .. } = &cx;
     let proj_generics = cx.proj_generics();
     let where_clause = item.generics.split_for_impl().2;
 
@@ -44,12 +42,12 @@ pub(super) fn parse(cx: &mut Context, mut item: ItemStruct) -> Result<TokenStrea
     };
 
     let project_body = quote! {
-        let this = self.as_mut().get_unchecked_mut();
-        #proj_ident #proj_init
+        let #orig_ident #proj_pat = self.as_mut().get_unchecked_mut();
+        #proj_ident #proj_body
     };
     let project_into_body = quote! {
-        let this = self.get_unchecked_mut();
-        #proj_ident #proj_init
+        let #orig_ident #proj_pat = self.get_unchecked_mut();
+        #proj_ident #proj_body
     };
 
     proj_items.extend(cx.make_proj_impl(&project_body, &project_into_body));
@@ -58,74 +56,3 @@ pub(super) fn parse(cx: &mut Context, mut item: ItemStruct) -> Result<TokenStrea
     item.extend(proj_items);
     Ok(item)
 }
-
-fn named(
-    cx: &mut Context,
-    FieldsNamed { named: fields, .. }: &mut FieldsNamed,
-) -> Result<(TokenStream, TokenStream)> {
-    let mut proj_fields = Vec::with_capacity(fields.len());
-    let mut proj_init = Vec::with_capacity(fields.len());
-    for Field { attrs, ident, ty, .. } in fields {
-        let cfg = collect_cfg(attrs);
-        if cx.find_pin_attr(attrs)? {
-            let lifetime = &cx.lifetime;
-            proj_fields.push(quote! {
-                #(#cfg)* #ident: ::core::pin::Pin<&#lifetime mut #ty>
-            });
-            proj_init.push(quote! {
-                #(#cfg)* #ident: ::core::pin::Pin::new_unchecked(&mut this.#ident)
-            });
-        } else {
-            let lifetime = &cx.lifetime;
-            proj_fields.push(quote! {
-                #(#cfg)* #ident: &#lifetime mut #ty
-            });
-            proj_init.push(quote! {
-                #(#cfg)* #ident: &mut this.#ident
-            });
-        }
-    }
-
-    let proj_fields = quote!({ #(#proj_fields,)* });
-    let proj_init = quote!({ #(#proj_init,)* });
-    Ok((proj_fields, proj_init))
-}
-
-fn unnamed(
-    cx: &mut Context,
-    FieldsUnnamed { unnamed: fields, .. }: &mut FieldsUnnamed,
-) -> Result<(TokenStream, TokenStream)> {
-    let mut proj_fields = Vec::with_capacity(fields.len());
-    let mut proj_init = Vec::with_capacity(fields.len());
-    for (index, Field { attrs, ty, .. }) in fields.iter_mut().enumerate() {
-        let index = Index::from(index);
-        let cfg = collect_cfg(attrs);
-        if !cfg.is_empty() {
-            return Err(error!(
-                cfg.first(),
-                "`cfg` attributes on the field of tuple structs are not supported"
-            ));
-        }
-        if cx.find_pin_attr(attrs)? {
-            let lifetime = &cx.lifetime;
-            proj_fields.push(quote! {
-                ::core::pin::Pin<&#lifetime mut #ty>
-            });
-            proj_init.push(quote! {
-                ::core::pin::Pin::new_unchecked(&mut this.#index)
-            });
-        } else {
-            let lifetime = &cx.lifetime;
-            proj_fields.push(quote! {
-                &#lifetime mut #ty
-            });
-            proj_init.push(quote! {
-                &mut this.#index
-            });
-        }
-    }
-
-    let proj_fields = quote!((#(#proj_fields,)*););
-    let proj_init = quote!((#(#proj_init,)*));
-    Ok((proj_fields, proj_init))
-}

tests/ui/cfg/auxiliary/sneaky_macro.rs

@@ -0,0 +1,62 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+
+use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};
+
+fn op(c: char) -> TokenTree {
+    Punct::new(c, Spacing::Alone).into()
+}
+
+fn ident(sym: &str) -> Ident {
+    Ident::new(sym, Span::call_site())
+}
+
+fn word(sym: &str) -> TokenTree {
+    ident(sym).into()
+}
+
+#[proc_macro_attribute]
+pub fn add_pinned_field(_: TokenStream, input: TokenStream) -> TokenStream {
+    let mut tokens: Vec<_> = input.into_iter().collect();
+    if let Some(TokenTree::Group(g)) = tokens.pop() {
+        let mut vec = vec![];
+        vec.extend(g.stream());
+
+        // #[pin]
+        // __field: __HiddenPinnedField
+        vec.push(op('#'));
+        vec.push(TokenTree::Group(Group::new(Delimiter::Bracket, word("pin").into())));
+        vec.push(word("__field"));
+        vec.push(op(':'));
+        vec.push(word("__HiddenPinnedField"));
+
+        tokens.extend(TokenStream::from(TokenTree::Group(Group::new(
+            Delimiter::Brace,
+            vec.into_iter().collect(),
+        ))));
+        let mut vec = vec![];
+
+        // pub struct __HiddenPinnedField;
+        vec.push(word("pub"));
+        vec.push(word("struct"));
+        vec.push(word("__HiddenPinnedField"));
+        vec.push(op(';'));
+
+        // impl !Unpin for __HiddenPinnedField {}
+        vec.push(word("impl"));
+        vec.push(op('!'));
+        vec.push(word("Unpin"));
+        vec.push(word("for"));
+        vec.push(word("__HiddenPinnedField"));
+        vec.push(TokenTree::Group(Group::new(Delimiter::Brace, TokenStream::new())));
+        tokens.extend(vec);
+
+        tokens.into_iter().collect()
+    } else {
+        unreachable!()
+    }
+}

tests/ui/cfg/field_sneaky.rs

@@ -0,0 +1,19 @@
+// compile-fail
+// aux-build:sneaky_macro.rs
+
+#![feature(optin_builtin_traits)]
+#![feature(trivial_bounds)]
+
+#[macro_use]
+extern crate sneaky_macro;
+
+use pin_project::pin_project;
+
+#[pin_project] //~ ERROR pattern does not mention field `__field`
+#[add_pinned_field]
+struct Foo {
+    #[pin]
+    field: u32,
+}
+
+fn main() {}

tests/ui/cfg/field_sneaky.stderr

@@ -0,0 +1,9 @@
+error[E0027]: pattern does not mention field `__field`
+  --> $DIR/field_sneaky.rs:12:14
+   |
+12 | #[pin_project] //~ ERROR pattern does not mention field `__field`
+   |              ^ missing field `__field`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0027`.