pprust: Handle multi-stmt/no-expr ExprFnBlock

Fixes #12685

src/libsyntax/print/pprust.rs

@@ -1313,17 +1313,20 @@ pub fn print_expr(&mut self, expr: &ast::Expr) -> IoResult<()> {
                 try!(self.print_fn_block_args(decl));
                 try!(space(&mut self.s));
                 // }
-                assert!(body.stmts.is_empty());
-                assert!(body.expr.is_some());
-                // we extract the block, so as not to create another set of boxes
-                match body.expr.unwrap().node {
-                    ast::ExprBlock(blk) => {
-                        try!(self.print_block_unclosed(blk));
-                    }
-                    _ => {
-                        // this is a bare expression
-                        try!(self.print_expr(body.expr.unwrap()));
-                        try!(self.end()); // need to close a box
+
+                if !body.stmts.is_empty() || !body.expr.is_some() {
+                    try!(self.print_block_unclosed(body));
+                } else {
+                    // we extract the block, so as not to create another set of boxes
+                    match body.expr.unwrap().node {
+                        ast::ExprBlock(blk) => {
+                            try!(self.print_block_unclosed(blk));
+                        }
+                        _ => {
+                            // this is a bare expression
+                            try!(self.print_expr(body.expr.unwrap()));
+                            try!(self.end()); // need to close a box
+                        }
                     }
                 }
                 // a box will be closed by print_expr, but we didn't want an overall

src/test/run-make/pretty-expanded/Makefile

@@ -0,0 +1,4 @@
+-include ../tools.mk
+
+all:
+	$(RUSTC) -o $(TMPDIR)/input.expanded.rs --pretty=expanded input.rs

src/test/run-make/pretty-expanded/input.rs

@@ -0,0 +1,22 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[crate_type="lib"]
+
+// #13544
+
+extern crate serialize;
+
+#[deriving(Encodable)] pub struct A;
+#[deriving(Encodable)] pub struct B(int);
+#[deriving(Encodable)] pub struct C { x: int }
+#[deriving(Encodable)] pub enum D {}
+#[deriving(Encodable)] pub enum E { y }
+#[deriving(Encodable)] pub enum F { z(int) }