Improve `Eq` deriving

1 files changed, 18 insertions, 0 deletions

diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 3dcdbc89096..b81d95a6998 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -97,6 +97,7 @@ pub trait AstBuilder {
                       typ: P<ast::Ty>,
                       ex: P<ast::Expr>)
                       -> P<ast::Stmt>;
+    fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt;
     fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt;
 
     // blocks
@@ -577,6 +578,23 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
+    // Generate `let _: Type;`, usually used for type assertions.
+    fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt {
+        let local = P(ast::Local {
+            pat: self.pat_wild(span),
+            ty: Some(ty),
+            init: None,
+            id: ast::DUMMY_NODE_ID,
+            span: span,
+            attrs: ast::ThinVec::new(),
+        });
+        ast::Stmt {
+            id: ast::DUMMY_NODE_ID,
+            node: ast::StmtKind::Local(local),
+            span: span,
+        }
+    }
+
     fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt {
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,