diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs index cf6262bda97..b84a1deb611 100644 --- a/src/libcore/fmt/mod.rs +++ b/src/libcore/fmt/mod.rs @@ -1700,8 +1700,18 @@ impl Debug for RefCell { .finish() } Err(_) => { + // The RefCell is mutably borrowed so we can't look at its value + // here. Show a placeholder instead. + struct BorrowedPlaceholder; + + impl Debug for BorrowedPlaceholder { + fn fmt(&self, f: &mut Formatter) -> Result { + f.write_str("") + } + } + f.debug_struct("RefCell") - .field("value", &"") + .field("value", &BorrowedPlaceholder) .finish() } } diff --git a/src/test/run-pass/ifmt.rs b/src/test/run-pass/ifmt.rs index cef2f879f9c..08e9990511f 100644 --- a/src/test/run-pass/ifmt.rs +++ b/src/test/run-pass/ifmt.rs @@ -13,6 +13,7 @@ #![allow(unused_features)] #![feature(box_syntax)] +use std::cell::RefCell; use std::fmt::{self, Write}; use std::usize; @@ -240,6 +241,8 @@ pub fn main() { // test that trailing commas are acceptable format!("{}", "test",); format!("{foo}", foo="test",); + + test_refcell(); } // Basic test to make sure that we can invoke the `write!` macro with an @@ -319,3 +322,12 @@ fn test_once() { assert_eq!(format!("{0} {0} {0} {a} {a} {a}", foo(), a=foo()), "1 1 1 2 2 2".to_string()); } + +fn test_refcell() { + let refcell = RefCell::new(5); + assert_eq!(format!("{:?}", refcell), "RefCell { value: 5 }"); + let borrow = refcell.borrow_mut(); + assert_eq!(format!("{:?}", refcell), "RefCell { value: }"); + drop(borrow); + assert_eq!(format!("{:?}", refcell), "RefCell { value: 5 }"); +}