Move automatic generation of Unpin implementation to proc-macro-derive

To generate the correct `Unpin` implementation, we need to collect the
types of the pinned fields. However, since proc-macro-attribute is
applied before cfg, we cannot be collecting field types at this timing.
So instead of generating the `Unpin` implementation here, we need to
delegate automatic generation of the `Unpin` implementation to
proc-macro-derive.

azure-pipelines.yml

@@ -39,6 +39,7 @@ jobs:
   parameters:
     toolchain: nightly
     name: nightly
+    cross: true
 
 - job: compiletest
   pool:
@@ -49,7 +50,9 @@ jobs:
         toolchain: nightly
     - script: |
         cargo clean
-        RUSTFLAGS='--cfg compiletest --cfg pin_project_show_unpin_struct' cargo test -p pin-project --all-features --test compiletest
+        cargo test -p pin-project --all-features --test compiletest
+      env:
+        RUSTFLAGS: -Dwarnings --cfg compiletest --cfg pin_project_show_unpin_struct
       displayName: compiletest
 
 - job: clippy
@@ -122,5 +125,7 @@ jobs:
       parameters:
         toolchain: nightly
     - script: |
-        RUSTDOCFLAGS=-Dwarnings cargo doc --no-deps --all --all-features
+        cargo doc --no-deps --all --all-features
+      env:
+        RUSTDOCFLAGS: -Dwarnings
       displayName: cargo doc

ci/azure-test.yml

@@ -1,11 +1,19 @@
 parameters:
-  vmImage: ubuntu-16.04
   cmd: test
 
 jobs:
 - job: ${{ parameters.name }}
+  strategy:
+    matrix:
+      Linux:
+        vmImage: ubuntu-16.04
+      ${{ if parameters.cross }}:
+        MacOS:
+          vmImage: macOS-10.13
+        Windows:
+          vmImage: vs2017-win2016
   pool:
-    vmImage: ${{ parameters.vmImage }}
+    vmImage: $(vmImage)
 
   steps:
     - template: azure-install-rust.yml

compiletest.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+# A script to run compile tests with the same condition that pin-project executes with CI.
+
+rm -rf target/debug/deps/libpin_project* && RUSTFLAGS='--cfg compiletest --cfg pin_project_show_unpin_struct' cargo test -p pin-project --all-features --test compiletest

pin-project-internal/src/lib.rs

@@ -333,7 +333,8 @@ use syn::parse::Nothing;
 /// [`pinned_drop`]: ./attr.pinned_drop.html
 #[proc_macro_attribute]
 pub fn pin_project(args: TokenStream, input: TokenStream) -> TokenStream {
-    pin_project::attribute(args.into(), input.into()).into()
+    let input = syn::parse_macro_input!(input);
+    pin_project::attribute(args.into(), input).into()
 }
 
 // TODO: Move this doc into pin-project crate when https://github.com/rust-lang/rust/pull/62855 merged.
@@ -372,7 +373,8 @@ pub fn pin_project(args: TokenStream, input: TokenStream) -> TokenStream {
 #[proc_macro_attribute]
 pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
     let _: Nothing = syn::parse_macro_input!(args);
-    pinned_drop::attribute(input.into()).into()
+    let input = syn::parse_macro_input!(input);
+    pinned_drop::attribute(&input).into()
 }
 
 // TODO: Move this doc into pin-project crate when https://github.com/rust-lang/rust/pull/62855 merged.
@@ -493,7 +495,15 @@ pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
 #[proc_macro_attribute]
 pub fn project(args: TokenStream, input: TokenStream) -> TokenStream {
     let _: Nothing = syn::parse_macro_input!(args);
-    project::attribute(input.into()).into()
+    let input = syn::parse_macro_input!(input);
+    project::attribute(input).into()
+}
+
+#[doc(hidden)]
+#[proc_macro_derive(__PinProjectAutoImplUnpin, attributes(pin))]
+pub fn derive_unpin(input: TokenStream) -> TokenStream {
+    let input = syn::parse_macro_input!(input);
+    pin_project::derive(input).into()
 }
 
 #[cfg(feature = "renamed")]

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

@@ -1,16 +1,16 @@
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote, ToTokens};
-use syn::{parse::Nothing, Field, Fields, FieldsNamed, FieldsUnnamed, ItemEnum, Result, Variant};
+use syn::{Field, Fields, FieldsNamed, FieldsUnnamed, ItemEnum, Result, Variant};
 
-use crate::utils::VecExt;
+use crate::utils::collect_cfg;
 
-use super::{Context, PIN};
+use super::Context;
 
 pub(super) fn parse(cx: &mut Context, mut item: ItemEnum) -> Result<TokenStream> {
     if item.variants.is_empty() {
-        return Err(error!(
-            item,
-            "#[pin_project] attribute may not be used on enums without variants"
+        return Err(syn::Error::new(
+            item.brace_token.span,
+            "#[pin_project] attribute may not be used on enums without variants",
         ));
     }
     let has_field = item.variants.iter().try_fold(false, |has_field, v| {
@@ -62,17 +62,22 @@ pub(super) fn parse(cx: &mut Context, mut item: ItemEnum) -> Result<TokenStream>
 fn variants(cx: &mut Context, item: &mut ItemEnum) -> Result<(Vec<TokenStream>, Vec<TokenStream>)> {
     let mut proj_variants = Vec::with_capacity(item.variants.len());
     let mut proj_arms = Vec::with_capacity(item.variants.len());
-    for Variant { fields, ident, .. } in &mut item.variants {
+    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::Unit => (TokenStream::new(), TokenStream::new(), TokenStream::new()),
         };
+        let cfg = collect_cfg(attrs);
         let Context { orig_ident, proj_ident, .. } = &cx;
-        let proj_arm = quote!(#orig_ident::#ident #proj_pat => #proj_ident::#ident #proj_body );
-        let proj_variant = quote!(#ident #proj_fields);
-        proj_arms.push(proj_arm);
-        proj_variants.push(proj_variant);
+        proj_variants.push(quote! {
+            #(#cfg)* #ident #proj_fields
+        });
+        proj_arms.push(quote! {
+            #(#cfg)* #orig_ident::#ident #proj_pat => {
+                #proj_ident::#ident #proj_body
+            }
+        });
     }
 
     Ok((proj_variants, proj_arms))
@@ -86,18 +91,27 @@ fn named(
     let mut proj_body = Vec::with_capacity(fields.len());
     let mut proj_fields = Vec::with_capacity(fields.len());
     for Field { attrs, ident, ty, .. } in fields {
-        if let Some(attr) = attrs.find_remove(PIN) {
-            let _: Nothing = syn::parse2(attr.tokens)?;
-            cx.push_unpin_bounds(ty.clone());
+        let cfg = collect_cfg(attrs);
+        if cx.find_pin_attr(attrs)? {
             let lifetime = &cx.lifetime;
-            proj_fields.push(quote!(#ident: ::core::pin::Pin<&#lifetime mut #ty>));
-            proj_body.push(quote!(#ident: ::core::pin::Pin::new_unchecked(#ident)));
+            proj_fields.push(quote! {
+                #(#cfg)* #ident: ::core::pin::Pin<&#lifetime mut #ty>
+            });
+            proj_body.push(quote! {
+                #(#cfg)* #ident: ::core::pin::Pin::new_unchecked(#ident)
+            });
         } else {
             let lifetime = &cx.lifetime;
-            proj_fields.push(quote!(#ident: &#lifetime mut #ty));
-            proj_body.push(quote!(#ident));
+            proj_fields.push(quote! {
+                #(#cfg)* #ident: &#lifetime mut #ty
+            });
+            proj_body.push(quote! {
+                #(#cfg)* #ident: #ident
+            });
         }
-        proj_pat.push(ident);
+        proj_pat.push(quote! {
+            #(#cfg)* #ident
+        });
     }
 
     let proj_pat = quote!({ #(#proj_pat),* });
@@ -114,19 +128,34 @@ fn unnamed(
     let mut proj_body = Vec::with_capacity(fields.len());
     let mut proj_fields = Vec::with_capacity(fields.len());
     for (i, Field { attrs, ty, .. }) in fields.iter_mut().enumerate() {
-        let x = format_ident!("_x{}", i);
-        if let Some(attr) = attrs.find_remove(PIN) {
-            let _: Nothing = syn::parse2(attr.tokens)?;
-            cx.push_unpin_bounds(ty.clone());
+        let id = format_ident!("_x{}", i);
+        let cfg = collect_cfg(attrs);
+        if !cfg.is_empty() {
+            return Err(error!(
+                cfg.first(),
+                "`cfg` attributes on the field of tuple variants are not supported"
+            ));
+        }
+        if cx.find_pin_attr(attrs)? {
             let lifetime = &cx.lifetime;
-            proj_fields.push(quote!(::core::pin::Pin<&#lifetime mut #ty>));
-            proj_body.push(quote!(::core::pin::Pin::new_unchecked(#x)));
+            proj_fields.push(quote! {
+                ::core::pin::Pin<&#lifetime mut #ty>
+            });
+            proj_body.push(quote! {
+                ::core::pin::Pin::new_unchecked(#id)
+            });
         } else {
             let lifetime = &cx.lifetime;
-            proj_fields.push(quote!(&#lifetime mut #ty));
-            proj_body.push(quote!(#x));
+            proj_fields.push(quote! {
+                &#lifetime mut #ty
+            });
+            proj_body.push(quote! {
+                #id
+            });
         }
-        proj_pat.push(x);
+        proj_pat.push(quote! {
+            #id
+        });
     }
 
     let proj_pat = quote!((#(#proj_pat),*));