4 files changed, 25 insertions, 2 deletions
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 0668730b3ef..2fe0ebcdd28 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -888,6 +888,17 @@ pub struct Local {
     pub id: NodeId,
     pub span: Span,
     pub attrs: ThinVec<Attribute>,
+    /// Origin of this local variable.
+    pub source: LocalSource,
+}
+
+#[derive(Clone, Copy, RustcEncodable, RustcDecodable, Debug)]
+pub enum LocalSource {
+    /// Local was parsed from source.
+    Normal,
+    /// Within `ast::IsAsync::Async`, a local is generated that will contain the moved arguments
+    /// of an `async fn`.
+    AsyncFn,
 }
 
 /// An arm of a 'match'.
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 614967bdeb4..029c45eaa72 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -526,6 +526,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             span: sp,
             attrs: ThinVec::new(),
+            source: ast::LocalSource::Normal,
         });
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
@@ -554,6 +555,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             span: sp,
             attrs: ThinVec::new(),
+            source: ast::LocalSource::Normal,
         });
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
@@ -571,6 +573,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             span,
             attrs: ThinVec::new(),
+            source: ast::LocalSource::Normal,
         });
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
diff --git a/src/libsyntax/mut_visit.rs b/src/libsyntax/mut_visit.rs
index 784d0049ac5..87826ccc891 100644
--- a/src/libsyntax/mut_visit.rs
+++ b/src/libsyntax/mut_visit.rs
@@ -208,6 +208,10 @@ pub trait MutVisitor: Sized {
         noop_visit_local(l, self);
     }
 
+    fn visit_local_source(&mut self, l: &mut LocalSource) {
+        noop_visit_local_source(l, self);
+    }
+
     fn visit_mac(&mut self, _mac: &mut Mac) {
         panic!("visit_mac disabled by default");
         // N.B., see note about macros above. If you really want a visitor that
@@ -511,13 +515,17 @@ pub fn noop_visit_parenthesized_parameter_data<T: MutVisitor>(args: &mut Parenth
 }
 
 pub fn noop_visit_local<T: MutVisitor>(local: &mut P<Local>, vis: &mut T) {
-    let Local { id, pat, ty, init, span, attrs } = local.deref_mut();
+    let Local { id, pat, ty, init, span, attrs, source } = local.deref_mut();
     vis.visit_id(id);
     vis.visit_pat(pat);
     visit_opt(ty, |ty| vis.visit_ty(ty));
     visit_opt(init, |init| vis.visit_expr(init));
     vis.visit_span(span);
     visit_thin_attrs(attrs, vis);
+    vis.visit_local_source(source);
+}
+
+pub fn noop_visit_local_source<T: MutVisitor>(_local_source: &mut LocalSource, _vis: &mut T) {
 }
 
 pub fn noop_visit_attribute<T: MutVisitor>(attr: &mut Attribute, vis: &mut T) {
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 8feab373e71..8620627765f 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -14,7 +14,7 @@ use crate::ast::{GenericParam, GenericParamKind};
 use crate::ast::GenericArg;
 use crate::ast::{Ident, ImplItem, IsAsync, IsAuto, Item, ItemKind};
 use crate::ast::{Label, Lifetime, Lit, LitKind};
-use crate::ast::Local;
+use crate::ast::{Local, LocalSource};
 use crate::ast::MacStmtStyle;
 use crate::ast::{Mac, Mac_, MacDelimiter};
 use crate::ast::{MutTy, Mutability};
@@ -5029,6 +5029,7 @@ impl<'a> Parser<'a> {
             id: ast::DUMMY_NODE_ID,
             span: lo.to(hi),
             attrs,
+            source: LocalSource::Normal,
         }))
     }