Auto merge of #51580 - cramertj:async-await, r=eddyb

async/await

This PR implements `async`/`await` syntax for `async fn` in Rust 2015 and `async` closures and `async` blocks in Rust 2018 (tracking issue: #50547). Limitations: non-`move` async closures with arguments are currently not supported, nor are `async fn` with multiple different input lifetimes. These limitations are not fundamental and will be removed in the future, however I'd like to go ahead and get this PR merged so we can start experimenting with this in combination with futures 0.3.

Based on #51414.
cc @petrochenkov for parsing changes.
r? @eddyb

src/librustc/diagnostics.rs

@@ -2131,5 +2131,10 @@ register_diagnostics! {
     E0657, // `impl Trait` can only capture lifetimes bound at the fn level
     E0687, // in-band lifetimes cannot be used in `fn`/`Fn` syntax
     E0688, // in-band lifetimes cannot be mixed with explicit lifetime binders
-    E0697, // closures cannot be static
+
+    E0906, // closures cannot be static
+
+    E0725, // multiple different lifetimes used in arguments of `async fn`
+    E0726, // multiple elided lifetimes used in arguments of `async fn`
+    E0727, // `async` non-`move` closures with arguments are not currently supported
 }

src/librustc/hir/intravisit.rs

@@ -41,7 +41,6 @@
 //! This order consistency is required in a few places in rustc, for
 //! example generator inference, and possibly also HIR borrowck.
 
-use rustc_target::spec::abi::Abi;
 use syntax::ast::{NodeId, CRATE_NODE_ID, Ident, Name, Attribute};
 use syntax_pos::Span;
 use hir::*;
@@ -54,8 +53,8 @@ use std::u32;
 
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub enum FnKind<'a> {
-    /// fn foo() or extern "Abi" fn foo()
-    ItemFn(Name, &'a Generics, Unsafety, Constness, Abi, &'a Visibility, &'a [Attribute]),
+    /// #[xxx] pub async/const/extern "Abi" fn foo()
+    ItemFn(Name, &'a Generics, FnHeader, &'a Visibility, &'a [Attribute]),
 
     /// fn foo(&self)
     Method(Name, &'a MethodSig, Option<&'a Visibility>, &'a [Attribute]),
@@ -479,12 +478,10 @@ pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item) {
             visitor.visit_ty(typ);
             visitor.visit_nested_body(body);
         }
-        ItemFn(ref declaration, unsafety, constness, abi, ref generics, body_id) => {
+        ItemFn(ref declaration, header, ref generics, body_id) => {
             visitor.visit_fn(FnKind::ItemFn(item.name,
                                             generics,
-                                            unsafety,
-                                            constness,
-                                            abi,
+                                            header,
                                             &item.vis,
                                             &item.attrs),
                              declaration,

src/librustc/hir/map/blocks.rs

@@ -25,7 +25,6 @@ use hir as ast;
 use hir::map::{self, Node};
 use hir::{Expr, FnDecl};
 use hir::intravisit::FnKind;
-use rustc_target::spec::abi;
 use syntax::ast::{Attribute, Name, NodeId};
 use syntax_pos::Span;
 
@@ -105,9 +104,7 @@ impl<'a> Code<'a> {
 struct ItemFnParts<'a> {
     name:     Name,
     decl:     &'a ast::FnDecl,
-    unsafety: ast::Unsafety,
-    constness: ast::Constness,
-    abi:      abi::Abi,
+    header:   ast::FnHeader,
     vis:      &'a ast::Visibility,
     generics: &'a ast::Generics,
     body:     ast::BodyId,
@@ -183,31 +180,31 @@ impl<'a> FnLikeNode<'a> {
 
     pub fn constness(self) -> ast::Constness {
         match self.kind() {
-            FnKind::ItemFn(_, _, _, constness, ..) => {
-                constness
-            }
-            FnKind::Method(_, m, ..) => {
-                m.constness
-            }
+            FnKind::ItemFn(_, _, header, ..) => header.constness,
+            FnKind::Method(_, m, ..) => m.header.constness,
             _ => ast::Constness::NotConst
         }
     }
 
+    pub fn asyncness(self) -> ast::IsAsync {
+        match self.kind() {
+            FnKind::ItemFn(_, _, header, ..) => header.asyncness,
+            FnKind::Method(_, m, ..) => m.header.asyncness,
+            _ => ast::IsAsync::NotAsync
+        }
+    }
+
     pub fn unsafety(self) -> ast::Unsafety {
         match self.kind() {
-            FnKind::ItemFn(_, _, unsafety, ..) => {
-                unsafety
-            }
-            FnKind::Method(_, m, ..) => {
-                m.unsafety
-            }
+            FnKind::ItemFn(_, _, header, ..) => header.unsafety,
+            FnKind::Method(_, m, ..) => m.header.unsafety,
             _ => ast::Unsafety::Normal
         }
     }
 
     pub fn kind(self) -> FnKind<'a> {
         let item = |p: ItemFnParts<'a>| -> FnKind<'a> {
-            FnKind::ItemFn(p.name, p.generics, p.unsafety, p.constness, p.abi, p.vis, p.attrs)
+            FnKind::ItemFn(p.name, p.generics, p.header, p.vis, p.attrs)
         };
         let closure = |c: ClosureParts<'a>| {
             FnKind::Closure(c.attrs)
@@ -232,19 +229,17 @@ impl<'a> FnLikeNode<'a> {
     {
         match self.node {
             map::NodeItem(i) => match i.node {
-                ast::ItemFn(ref decl, unsafety, constness, abi, ref generics, block) =>
+                ast::ItemFn(ref decl, header, ref generics, block) =>
                     item_fn(ItemFnParts {
                         id: i.id,
                         name: i.name,
                         decl: &decl,
-                        unsafety,
                         body: block,
-                        generics,
-                        abi,
                         vis: &i.vis,
-                        constness,
                         span: i.span,
                         attrs: &i.attrs,
+                        header,
+                        generics,
                     }),
                 _ => bug!("item FnLikeNode that is not fn-like"),
             },

src/librustc/hir/map/def_collector.rs

@@ -73,6 +73,27 @@ impl<'a> DefCollector<'a> {
         self.parent_def = parent;
     }
 
+    fn visit_async_fn(
+        &mut self,
+        id: NodeId,
+        async_node_id: NodeId,
+        name: Name,
+        span: Span,
+        visit_fn: impl FnOnce(&mut DefCollector<'a>)
+    ) {
+        // For async functions, we need to create their inner defs inside of a
+        // closure to match their desugared representation.
+        let fn_def_data = DefPathData::ValueNs(name.as_interned_str());
+        let fn_def = self.create_def(id, fn_def_data, ITEM_LIKE_SPACE, span);
+        return self.with_parent(fn_def, |this| {
+            let closure_def = this.create_def(async_node_id,
+                                  DefPathData::ClosureExpr,
+                                  REGULAR_SPACE,
+                                  span);
+            this.with_parent(closure_def, visit_fn)
+        })
+    }
+
     fn visit_macro_invoc(&mut self, id: NodeId) {
         if let Some(ref mut visit) = self.visit_macro_invoc {
             visit(MacroInvocationData {
@@ -99,6 +120,15 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             ItemKind::Mod(..) if i.ident == keywords::Invalid.ident() => {
                 return visit::walk_item(self, i);
             }
+            ItemKind::Fn(_, FnHeader { asyncness: IsAsync::Async(async_node_id), .. }, ..) => {
+                return self.visit_async_fn(
+                    i.id,
+                    async_node_id,
+                    i.ident.name,
+                    i.span,
+                    |this| visit::walk_item(this, i)
+                )
+            }
             ItemKind::Mod(..) => DefPathData::Module(i.ident.name.as_interned_str()),
             ItemKind::Static(..) | ItemKind::Const(..) | ItemKind::Fn(..) =>
                 DefPathData::ValueNs(i.ident.name.as_interned_str()),
@@ -197,6 +227,17 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
 
     fn visit_impl_item(&mut self, ii: &'a ImplItem) {
         let def_data = match ii.node {
+            ImplItemKind::Method(MethodSig {
+                header: FnHeader { asyncness: IsAsync::Async(async_node_id), .. }, ..
+            }, ..) => {
+                return self.visit_async_fn(
+                    ii.id,
+                    async_node_id,
+                    ii.ident.name,
+                    ii.span,
+                    |this| visit::walk_impl_item(this, ii)
+                )
+            }
             ImplItemKind::Method(..) | ImplItemKind::Const(..) =>
                 DefPathData::ValueNs(ii.ident.name.as_interned_str()),
             ImplItemKind::Type(..) => DefPathData::AssocTypeInImpl(ii.ident.name.as_interned_str()),
@@ -227,15 +268,32 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
 
         match expr.node {
             ExprKind::Mac(..) => return self.visit_macro_invoc(expr.id),
-            ExprKind::Closure(..) => {
-                let def = self.create_def(expr.id,
+            ExprKind::Closure(_, asyncness, ..) => {
+                let closure_def = self.create_def(expr.id,
                                           DefPathData::ClosureExpr,
                                           REGULAR_SPACE,
                                           expr.span);
-                self.parent_def = Some(def);
+                self.parent_def = Some(closure_def);
+
+                // Async closures desugar to closures inside of closures, so
+                // we must create two defs.
+                if let IsAsync::Async(async_id) = asyncness {
+                    let async_def = self.create_def(async_id,
+                                                    DefPathData::ClosureExpr,
+                                                    REGULAR_SPACE,
+                                                    expr.span);
+                    self.parent_def = Some(async_def);
+                }
+            }
+            ExprKind::Async(_, async_id, _) => {
+                let async_def = self.create_def(async_id,
+                                                DefPathData::ClosureExpr,
+                                                REGULAR_SPACE,
+                                                expr.span);
+                self.parent_def = Some(async_def);
             }
             _ => {}
-        }
+        };
 
         visit::walk_expr(self, expr);
         self.parent_def = parent_def;

src/librustc/hir/map/mod.rs

@@ -174,7 +174,7 @@ impl<'hir> MapEntry<'hir> {
         match self {
             EntryItem(_, _, ref item) => {
                 match item.node {
-                    ItemFn(ref fn_decl, _, _, _, _, _) => Some(&fn_decl),
+                    ItemFn(ref fn_decl, _, _, _) => Some(&fn_decl),
                     _ => None,
                 }
             }
@@ -210,7 +210,7 @@ impl<'hir> MapEntry<'hir> {
                 match item.node {
                     ItemConst(_, body) |
                     ItemStatic(.., body) |
-                    ItemFn(_, _, _, _, _, body) => Some(body),
+                    ItemFn(_, _, _, body) => Some(body),
                     _ => None,
                 }
             }

src/librustc/hir/mod.rs

@@ -255,7 +255,7 @@ impl LifetimeName {
         }
     }
 
-    fn is_elided(&self) -> bool {
+    pub fn is_elided(&self) -> bool {
         use self::LifetimeName::*;
         match self {
             Implicit | Underscore => true,
@@ -1506,9 +1506,7 @@ pub struct MutTy {
 /// Represents a method's signature in a trait declaration or implementation.
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct MethodSig {
-    pub unsafety: Unsafety,
-    pub constness: Constness,
-    pub abi: Abi,
+    pub header: FnHeader,
     pub decl: P<FnDecl>,
 }
 
@@ -1736,7 +1734,13 @@ pub enum IsAuto {
     No
 }
 
-#[derive(Copy, Clone, PartialEq, Eq,PartialOrd, Ord, RustcEncodable, RustcDecodable, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub enum IsAsync {
+    Async,
+    NotAsync,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum Unsafety {
     Unsafe,
     Normal,
@@ -2012,6 +2016,14 @@ pub struct Item {
     pub span: Span,
 }
 
+#[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub struct FnHeader {
+    pub unsafety: Unsafety,
+    pub constness: Constness,
+    pub asyncness: IsAsync,
+    pub abi: Abi,
+}
+
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum Item_ {
     /// An `extern crate` item, with optional *original* crate name if the crate was renamed.
@@ -2031,7 +2043,7 @@ pub enum Item_ {
     /// A `const` item
     ItemConst(P<Ty>, BodyId),
     /// A function declaration
-    ItemFn(P<FnDecl>, Unsafety, Constness, Abi, Generics, BodyId),
+    ItemFn(P<FnDecl>, FnHeader, Generics, BodyId),
     /// A module
     ItemMod(Mod),
     /// An external module
@@ -2096,7 +2108,7 @@ impl Item_ {
 
     pub fn generics(&self) -> Option<&Generics> {
         Some(match *self {
-            ItemFn(_, _, _, _, ref generics, _) |
+            ItemFn(_, _, ref generics, _) |
             ItemTy(_, ref generics) |
             ItemEnum(_, ref generics) |
             ItemStruct(_, ref generics) |