Implement `fmt::Debug` for all structures in libstd.

Part of https://github.com/rust-lang/rust/issues/31869.

Also turn on the `missing_debug_implementations` lint at the crate
level.

src/libstd/ascii.rs

@@ -12,6 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use fmt;
 use mem;
 use ops::Range;
 use iter::FusedIterator;
@@ -370,6 +371,13 @@ impl ExactSizeIterator for EscapeDefault {}
 #[unstable(feature = "fused", issue = "35602")]
 impl FusedIterator for EscapeDefault {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for EscapeDefault {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("EscapeDefault { .. }")
+    }
+}
+
 
 static ASCII_LOWERCASE_MAP: [u8; 256] = [
     0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,

src/libstd/collections/hash/map.rs

@@ -1276,6 +1276,15 @@ fn clone(&self) -> Iter<'a, K, V> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K: Debug, V: Debug> fmt::Debug for Iter<'a, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 /// HashMap mutable values iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IterMut<'a, K: 'a, V: 'a> {
@@ -1285,7 +1294,7 @@ pub struct IterMut<'a, K: 'a, V: 'a> {
 /// HashMap move iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoIter<K, V> {
-    inner: table::IntoIter<K, V>,
+    pub(super) inner: table::IntoIter<K, V>,
 }
 
 /// HashMap keys iterator.
@@ -1302,6 +1311,15 @@ fn clone(&self) -> Keys<'a, K, V> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K: Debug, V: Debug> fmt::Debug for Keys<'a, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 /// HashMap values iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Values<'a, K: 'a, V: 'a> {
@@ -1316,10 +1334,19 @@ fn clone(&self) -> Values<'a, K, V> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K: Debug, V: Debug> fmt::Debug for Values<'a, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 /// HashMap drain iterator.
 #[stable(feature = "drain", since = "1.6.0")]
 pub struct Drain<'a, K: 'a, V: 'a> {
-    inner: table::Drain<'a, K, V>,
+    pub(super) inner: table::Drain<'a, K, V>,
 }
 
 /// Mutable HashMap values iterator.
@@ -1557,6 +1584,18 @@ fn len(&self) -> usize {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K, V> fmt::Debug for IterMut<'a, K, V>
+    where K: fmt::Debug,
+          V: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.inner.iter())
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K, V> Iterator for IntoIter<K, V> {
     type Item = (K, V);
@@ -1580,6 +1619,15 @@ fn len(&self) -> usize {
 #[unstable(feature = "fused", issue = "35602")]
 impl<K, V> FusedIterator for IntoIter<K, V> {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.inner.iter())
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, K, V> Iterator for Keys<'a, K, V> {
     type Item = &'a K;
@@ -1649,6 +1697,18 @@ fn len(&self) -> usize {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K, V> FusedIterator for ValuesMut<'a, K, V> {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K, V> fmt::Debug for ValuesMut<'a, K, V>
+    where K: fmt::Debug,
+          V: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.inner.inner.iter())
+            .finish()
+    }
+}
+
 #[stable(feature = "drain", since = "1.6.0")]
 impl<'a, K, V> Iterator for Drain<'a, K, V> {
     type Item = (K, V);
@@ -1672,6 +1732,18 @@ fn len(&self) -> usize {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K, V> FusedIterator for Drain<'a, K, V> {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K, V> fmt::Debug for Drain<'a, K, V>
+    where K: fmt::Debug,
+          V: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.inner.iter())
+            .finish()
+    }
+}
+
 impl<'a, K, V> Entry<'a, K, V> {
     #[stable(feature = "rust1", since = "1.0.0")]
     /// Ensures a value is in the entry by inserting the default if empty, and returns
@@ -2148,6 +2220,13 @@ fn default() -> RandomState {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for RandomState {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("RandomState { .. }")
+    }
+}
+
 impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
     where K: Eq + Hash + Borrow<Q>,
           S: BuildHasher,

src/libstd/collections/hash/set.rs

@@ -948,6 +948,15 @@ fn len(&self) -> usize {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K> FusedIterator for Iter<'a, K> {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K: fmt::Debug> fmt::Debug for Iter<'a, K> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K> Iterator for IntoIter<K> {
     type Item = K;
@@ -968,6 +977,16 @@ fn len(&self) -> usize {
 #[unstable(feature = "fused", issue = "35602")]
 impl<K> FusedIterator for IntoIter<K> {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<K: fmt::Debug> fmt::Debug for IntoIter<K> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let entries_iter = self.iter.inner.iter().map(|(k, _)| k);
+        f.debug_list()
+            .entries(entries_iter)
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, K> Iterator for Drain<'a, K> {
     type Item = K;
@@ -988,6 +1007,16 @@ fn len(&self) -> usize {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K> FusedIterator for Drain<'a, K> {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, K: fmt::Debug> fmt::Debug for Drain<'a, K> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let entries_iter = self.iter.inner.iter().map(|(k, _)| k);
+        f.debug_list()
+            .entries(entries_iter)
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T, S> Clone for Intersection<'a, T, S> {
     fn clone(&self) -> Intersection<'a, T, S> {
@@ -1021,6 +1050,18 @@ fn size_hint(&self) -> (usize, Option<usize>) {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, T, S> fmt::Debug for Intersection<'a, T, S>
+    where T: fmt::Debug + Eq + Hash,
+          S: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, T, S> FusedIterator for Intersection<'a, T, S>
     where T: Eq + Hash,
@@ -1068,6 +1109,18 @@ impl<'a, T, S> FusedIterator for Difference<'a, T, S>
 {
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, T, S> fmt::Debug for Difference<'a, T, S>
+    where T: fmt::Debug + Eq + Hash,
+          S: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T, S> Clone for SymmetricDifference<'a, T, S> {
     fn clone(&self) -> SymmetricDifference<'a, T, S> {
@@ -1097,6 +1150,18 @@ impl<'a, T, S> FusedIterator for SymmetricDifference<'a, T, S>
 {
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, T, S> fmt::Debug for SymmetricDifference<'a, T, S>
+    where T: fmt::Debug + Eq + Hash,
+          S: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T, S> Clone for Union<'a, T, S> {
     fn clone(&self) -> Union<'a, T, S> {
@@ -1111,6 +1176,18 @@ impl<'a, T, S> FusedIterator for Union<'a, T, S>
 {
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, T, S> fmt::Debug for Union<'a, T, S>
+    where T: fmt::Debug + Eq + Hash,
+          S: BuildHasher,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(self.clone())
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T, S> Iterator for Union<'a, T, S>
     where T: Eq + Hash,

src/libstd/collections/hash/table.rs

@@ -882,6 +882,15 @@ unsafe impl<'a, K: Sync, V: Sync> Sync for IterMut<'a, K, V> {}
 // but Send is the more useful bound
 unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
 
+impl<'a, K: 'a, V: 'a> IterMut<'a, K, V> {
+    pub fn iter(&self) -> Iter<K, V> {
+        Iter {
+            iter: self.iter.clone(),
+            elems_left: self.elems_left,
+        }
+    }
+}
+
 /// Iterator over the entries in a table, consuming the table.
 pub struct IntoIter<K, V> {
     table: RawTable<K, V>,
@@ -891,6 +900,15 @@ pub struct IntoIter<K, V> {
 unsafe impl<K: Sync, V: Sync> Sync for IntoIter<K, V> {}
 unsafe impl<K: Send, V: Send> Send for IntoIter<K, V> {}
 
+impl<K, V> IntoIter<K, V> {
+    pub fn iter(&self) -> Iter<K, V> {
+        Iter {
+            iter: self.iter.clone(),
+            elems_left: self.table.size,
+        }
+    }
+}
+
 /// Iterator over the entries in a table, clearing the table.
 pub struct Drain<'a, K: 'a, V: 'a> {
     table: Shared<RawTable<K, V>>,
@@ -901,6 +919,17 @@ pub struct Drain<'a, K: 'a, V: 'a> {
 unsafe impl<'a, K: Sync, V: Sync> Sync for Drain<'a, K, V> {}
 unsafe impl<'a, K: Send, V: Send> Send for Drain<'a, K, V> {}
 
+impl<'a, K, V> Drain<'a, K, V> {
+    pub fn iter(&self) -> Iter<K, V> {
+        unsafe {
+            Iter {
+                iter: self.iter.clone(),
+                elems_left: (**self.table).size,
+            }
+        }
+    }
+}
+
 impl<'a, K, V> Iterator for Iter<'a, K, V> {
     type Item = (&'a K, &'a V);
 

src/libstd/env.rs

@@ -143,6 +143,13 @@ fn next(&mut self) -> Option<(String, String)> {
     fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Vars {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Vars { .. }")
+    }
+}
+
 #[stable(feature = "env", since = "1.0.0")]
 impl Iterator for VarsOs {
     type Item = (OsString, OsString);
@@ -150,6 +157,13 @@ fn next(&mut self) -> Option<(OsString, OsString)> { self.inner.next() }
     fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for VarsOs {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("VarsOs { .. }")
+    }
+}
+
 /// Fetches the environment variable `key` from the current process.
 ///
 /// The returned result is `Ok(s)` if the environment variable is present and is
@@ -364,6 +378,13 @@ fn next(&mut self) -> Option<PathBuf> { self.inner.next() }
     fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a> fmt::Debug for SplitPaths<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("SplitPaths { .. }")
+    }
+}
+
 /// Error type returned from `std::env::join_paths` when paths fail to be
 /// joined.
 #[derive(Debug)]
@@ -640,6 +661,13 @@ fn next_back(&mut self) -> Option<String> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Args {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Args { .. }")
+    }
+}
+
 #[stable(feature = "env", since = "1.0.0")]
 impl Iterator for ArgsOs {
     type Item = OsString;
@@ -657,6 +685,14 @@ fn is_empty(&self) -> bool { self.inner.is_empty() }
 impl DoubleEndedIterator for ArgsOs {
     fn next_back(&mut self) -> Option<OsString> { self.inner.next_back() }
 }
+
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for ArgsOs {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("ArgsOs { .. }")
+    }
+}
+
 /// Constants associated with the current target
 #[stable(feature = "env", since = "1.0.0")]
 pub mod consts {

src/libstd/fs.rs

@@ -140,7 +140,7 @@ pub struct File {
 ///             .create(true)
 ///             .open("foo.txt");
 /// ```
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct OpenOptions(fs_imp::OpenOptions);
 
@@ -168,6 +168,7 @@ pub struct File {
 ///
 /// This builder also supports platform-specific options.
 #[stable(feature = "dir_builder", since = "1.6.0")]
+#[derive(Debug)]
 pub struct DirBuilder {
     inner: fs_imp::DirBuilder,
     recursive: bool,
@@ -834,6 +835,21 @@ pub fn created(&self) -> io::Result<SystemTime> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Metadata {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Metadata")
+            .field("file_type", &self.file_type())
+            .field("is_dir", &self.is_dir())
+            .field("is_file", &self.is_file())
+            .field("permissions", &self.permissions())
+            .field("modified", &self.modified())
+            .field("accessed", &self.accessed())
+            .field("created", &self.created())
+            .finish()
+    }
+}
+
 impl AsInner<fs_imp::FileAttr> for Metadata {
     fn as_inner(&self) -> &fs_imp::FileAttr { &self.0 }
 }

src/libstd/io/mod.rs

@@ -1444,6 +1444,16 @@ pub struct Chain<T, U> {
     done_first: bool,
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Chain")
+            .field("t", &self.first)
+            .field("u", &self.second)
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Read, U: Read> Read for Chain<T, U> {
     fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
@@ -1485,6 +1495,7 @@ fn consume(&mut self, amt: usize) {
 ///
 /// [`take()`]: trait.Read.html#method.take
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct Take<T> {
     inner: T,
     limit: u64,
@@ -1602,6 +1613,7 @@ fn read_one_byte(reader: &mut Read) -> Option<Result<u8>> {
 ///
 /// [`bytes()`]: trait.Read.html#method.bytes
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct Bytes<R> {
     inner: R,
 }
@@ -1623,6 +1635,7 @@ fn next(&mut self) -> Option<Result<u8>> {
 /// [chars]: trait.Read.html#method.chars
 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
            issue = "27802")]
+#[derive(Debug)]
 pub struct Chars<R> {
     inner: R,
 }
@@ -1712,6 +1725,7 @@ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 ///
 /// [split]: trait.BufRead.html#method.split
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct Split<B> {
     buf: B,
     delim: u8,
@@ -1743,6 +1757,7 @@ fn next(&mut self) -> Option<Result<Vec<u8>>> {
 ///
 /// [lines]: trait.BufRead.html#method.lines
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct Lines<B> {
     buf: B,
 }

src/libstd/io/stdio.rs

@@ -282,6 +282,13 @@ pub fn read_line(&self, buf: &mut String) -> io::Result<usize> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Stdin {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Stdin { .. }")
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Read for Stdin {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
@@ -314,6 +321,13 @@ fn fill_buf(&mut self) -> io::Result<&[u8]> { self.inner.fill_buf() }
     fn consume(&mut self, n: usize) { self.inner.consume(n) }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a> fmt::Debug for StdinLock<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("StdinLock { .. }")
+    }
+}
+
 /// A handle to the global standard output stream of the current process.
 ///
 /// Each handle shares a global buffer of data to be written to the standard
@@ -424,6 +438,13 @@ pub fn lock(&self) -> StdoutLock {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Stdout {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Stdout { .. }")
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Write for Stdout {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -449,6 +470,13 @@ fn flush(&mut self) -> io::Result<()> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a> fmt::Debug for StdoutLock<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("StdoutLock { .. }")
+    }
+}
+
 /// A handle to the standard error stream of a process.
 ///
 /// For more information, see the [`io::stderr`] method.
@@ -545,6 +573,13 @@ pub fn lock(&self) -> StderrLock {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Stderr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Stderr { .. }")
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Write for Stderr {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@@ -570,6 +605,13 @@ fn flush(&mut self) -> io::Result<()> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a> fmt::Debug for StderrLock<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("StderrLock { .. }")
+    }
+}
+
 /// Resets the thread-local stderr handle to the specified writer
 ///
 /// This will replace the current thread's stderr handle, returning the old

src/libstd/io/util.rs

@@ -10,6 +10,7 @@
 
 #![allow(missing_copy_implementations)]
 
+use fmt;
 use io::{self, Read, Write, ErrorKind, BufRead};
 
 /// Copies the entire contents of a reader into a writer.
@@ -97,6 +98,13 @@ fn fill_buf(&mut self) -> io::Result<&[u8]> { Ok(&[]) }
     fn consume(&mut self, _n: usize) {}
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Empty {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Empty { .. }")
+    }
+}
+
 /// A reader which yields one byte over and over and over and over and over and...
 ///
 /// This struct is generally created by calling [`repeat()`][repeat]. Please
@@ -133,6 +141,13 @@ fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Repeat {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Repeat { .. }")
+    }
+}
+
 /// A writer which will move data into the void.
 ///
 /// This struct is generally created by calling [`sink()`][sink]. Please
@@ -165,6 +180,13 @@ fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len()) }
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Sink {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Sink { .. }")
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use io::prelude::*;

src/libstd/lib.rs

@@ -214,6 +214,7 @@
 #![no_std]
 
 #![deny(missing_docs)]
+#![deny(missing_debug_implementations)]
 
 // Tell the compiler to link to either panic_abort or panic_unwind
 #![needs_panic_runtime]
@@ -276,6 +277,7 @@
 #![feature(panic_unwind)]
 #![feature(placement_in_syntax)]
 #![feature(prelude_import)]
+#![feature(pub_restricted)]
 #![feature(rand)]
 #![feature(raw)]
 #![feature(repr_simd)]

src/libstd/net/mod.rs

@@ -12,6 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use fmt;
 use io::{self, Error, ErrorKind};
 use sys_common::net as net_imp;
 
@@ -105,6 +106,13 @@ impl Iterator for LookupHost {
     fn next(&mut self) -> Option<SocketAddr> { self.0.next() }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for LookupHost {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("LookupHost { .. }")
+    }
+}
+
 /// Resolve the host specified by `host` as a number of `SocketAddr` instances.
 ///
 /// This method may perform a DNS query to resolve `host` and may also inspect

src/libstd/net/tcp.rs

@@ -76,6 +76,7 @@
 /// [`incoming`]: struct.TcpListener.html#method.incoming
 /// [`TcpListener`]: struct.TcpListener.html
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct Incoming<'a> { listener: &'a TcpListener }
 
 impl TcpStream {

src/libstd/os/linux/raw.rs

@@ -17,6 +17,7 @@
                               crates.io should be used instead for the correct \
                               definitions")]
 #![allow(deprecated)]
+#![allow(missing_debug_implementations)]
 
 use os::raw::c_ulong;
 

src/libstd/os/macos/raw.rs

@@ -33,7 +33,7 @@
 pub type pthread_t = usize;
 
 #[repr(C)]
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 #[stable(feature = "raw_ext", since = "1.1.0")]
 pub struct stat {
     #[stable(feature = "raw_ext", since = "1.1.0")]

src/libstd/os/raw.rs

@@ -12,6 +12,8 @@
 
 #![stable(feature = "raw_os", since = "1.1.0")]
 
+use fmt;
+
 #[cfg(any(target_os = "android",
           target_os = "emscripten",
           all(target_os = "linux", any(target_arch = "aarch64",
@@ -71,6 +73,13 @@ pub enum c_void {
     #[doc(hidden)] __variant2,
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for c_void {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("c_void")
+    }
+}
+
 #[cfg(test)]
 #[allow(unused_imports)]
 mod tests {

src/libstd/panic.rs

@@ -14,6 +14,7 @@
 
 use any::Any;
 use cell::UnsafeCell;
+use fmt;
 use ops::{Deref, DerefMut};
 use panicking;
 use ptr::{Unique, Shared};
@@ -296,6 +297,15 @@ extern "rust-call" fn call_once(self, _args: ()) -> R {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<T: fmt::Debug> fmt::Debug for AssertUnwindSafe<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("AssertUnwindSafe")
+            .field(&self.0)
+            .finish()
+    }
+}
+
 /// Invokes a closure, capturing the cause of an unwinding panic if one occurs.
 ///
 /// This function will return `Ok` with the closure's result if the closure

src/libstd/panicking.rs

@@ -177,6 +177,7 @@ pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
 /// panic!("Normal panic");
 /// ```
 #[stable(feature = "panic_hooks", since = "1.10.0")]
+#[derive(Debug)]
 pub struct PanicInfo<'a> {
     payload: &'a (Any + Send),
     location: Location<'a>,
@@ -256,6 +257,7 @@ pub fn location(&self) -> Option<&Location> {
 ///
 /// panic!("Normal panic");
 /// ```
+#[derive(Debug)]
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 pub struct Location<'a> {
     file: &'a str,

src/libstd/process.rs

@@ -114,6 +114,17 @@ impl IntoInner<imp::Process> for Child {
     fn into_inner(self) -> imp::Process { self.handle }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Child {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Child")
+            .field("stdin", &self.stdin)
+            .field("stdout", &self.stdout)
+            .field("stderr", &self.stderr)
+            .finish()
+    }
+}
+
 /// A handle to a child process's stdin. This struct is used in the [`stdin`]
 /// field on [`Child`].
 ///
@@ -149,6 +160,13 @@ fn from_inner(pipe: AnonPipe) -> ChildStdin {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for ChildStdin {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("ChildStdin { .. }")
+    }
+}
+
 /// A handle to a child process's stdout. This struct is used in the [`stdout`]
 /// field on [`Child`].
 ///
@@ -183,6 +201,13 @@ fn from_inner(pipe: AnonPipe) -> ChildStdout {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for ChildStdout {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("ChildStdout { .. }")
+    }
+}
+
 /// A handle to a child process's stderr. This struct is used in the [`stderr`]
 /// field on [`Child`].
 ///
@@ -217,6 +242,13 @@ fn from_inner(pipe: AnonPipe) -> ChildStderr {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for ChildStderr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("ChildStderr { .. }")
+    }
+}
+
 /// A process builder, providing fine-grained control
 /// over how a new process should be spawned.
 ///
@@ -622,6 +654,13 @@ fn from_inner(inner: imp::Stdio) -> Stdio {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Stdio {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Stdio { .. }")
+    }
+}
+
 /// Describes the result of a process after it has terminated.
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 #[stable(feature = "process", since = "1.0.0")]

src/libstd/rand/mod.rs

@@ -59,6 +59,7 @@
 #![unstable(feature = "rand", issue = "0")]
 
 use cell::RefCell;
+use fmt;
 use io;
 use mem;
 use rc::Rc;
@@ -143,6 +144,12 @@ pub struct ThreadRng {
     rng: Rc<RefCell<ThreadRngInner>>,
 }
 
+impl fmt::Debug for ThreadRng {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("ThreadRng { .. }")
+    }
+}
+
 /// Retrieve the lazily-initialized thread-local random number
 /// generator, seeded by the system. Intended to be used in method
 /// chaining style, e.g. `thread_rng().gen::<isize>()`.

src/libstd/sync/barrier.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use fmt;
 use sync::{Mutex, Condvar};
 
 /// A barrier enables multiple threads to synchronize the beginning
@@ -54,6 +55,13 @@ struct BarrierState {
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct BarrierWaitResult(bool);
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Barrier {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Barrier { .. }")
+    }
+}
+
 impl Barrier {
     /// Creates a new barrier that can block a given number of threads.
     ///
@@ -102,6 +110,15 @@ pub fn wait(&self) -> BarrierWaitResult {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for BarrierWaitResult {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("BarrierWaitResult")
+            .field("is_leader", &self.is_leader())
+            .finish()
+    }
+}
+
 impl BarrierWaitResult {
     /// Returns whether this thread from `wait` is the "leader thread".
     ///

src/libstd/sync/condvar.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use fmt;
 use sync::atomic::{AtomicUsize, Ordering};
 use sync::{mutex, MutexGuard, PoisonError};
 use sys_common::condvar as sys;
@@ -239,6 +240,13 @@ fn verify(&self, mutex: &sys_mutex::Mutex) {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Condvar {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Condvar { .. }")
+    }
+}
+
 #[stable(feature = "condvar_default", since = "1.9.0")]
 impl Default for Condvar {
     /// Creates a `Condvar` which is ready to be waited on and notified.

src/libstd/sync/mpsc/mod.rs

@@ -306,6 +306,7 @@ impl<T> !Sync for Receiver<T> { }
 /// whenever `next` is called, waiting for a new message, and `None` will be
 /// returned when the corresponding channel has hung up.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct Iter<'a, T: 'a> {
     rx: &'a Receiver<T>
 }
@@ -317,6 +318,7 @@ pub struct Iter<'a, T: 'a> {
 /// This Iterator will never block the caller in order to wait for data to
 /// become available. Instead, it will return `None`.
 #[stable(feature = "receiver_try_iter", since = "1.15.0")]
+#[derive(Debug)]
 pub struct TryIter<'a, T: 'a> {
     rx: &'a Receiver<T>
 }
@@ -325,6 +327,7 @@ pub struct TryIter<'a, T: 'a> {
 /// whenever `next` is called, waiting for a new message, and `None` will be
 /// returned when the corresponding channel has hung up.
 #[stable(feature = "receiver_into_iter", since = "1.1.0")]
+#[derive(Debug)]
 pub struct IntoIter<T> {
     rx: Receiver<T>
 }

src/libstd/sync/mutex.rs

@@ -351,6 +351,15 @@ fn drop(&mut self) {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("MutexGuard")
+            .field("lock", &self.__lock)
+            .finish()
+    }
+}
+
 pub fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::Mutex {
     &guard.__lock.inner
 }

src/libstd/sync/once.rs

@@ -64,6 +64,7 @@
 // You'll find a few more details in the implementation, but that's the gist of
 // it!
 
+use fmt;
 use marker;
 use ptr;
 use sync::atomic::{AtomicUsize, AtomicBool, Ordering};
@@ -103,6 +104,7 @@ unsafe impl Send for Once {}
 /// State yielded to the `call_once_force` method which can be used to query
 /// whether the `Once` was previously poisoned or not.
 #[unstable(feature = "once_poison", issue = "33577")]
+#[derive(Debug)]
 pub struct OnceState {
     poisoned: bool,
 }
@@ -328,6 +330,13 @@ fn call_inner(&'static self,
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for Once {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Once { .. }")
+    }
+}
+
 impl Drop for Finish {
     fn drop(&mut self) {
         // Swap out our state with however we finished. We should only ever see

src/libstd/sync/rwlock.rs

@@ -362,6 +362,24 @@ unsafe fn new(lock: &'rwlock RwLock<T>)
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, T: fmt::Debug> fmt::Debug for RwLockReadGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("RwLockReadGuard")
+            .field("lock", &self.__lock)
+            .finish()
+    }
+}
+
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<'a, T: fmt::Debug> fmt::Debug for RwLockWriteGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("RwLockWriteGuard")
+            .field("lock", &self.__lock)
+            .finish()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> {
     type Target = T;

src/libstd/sys/unix/fast_thread_local.rs

@@ -12,6 +12,7 @@
 #![unstable(feature = "thread_local_internals", issue = "0")]
 
 use cell::{Cell, UnsafeCell};
+use fmt;
 use intrinsics;
 use ptr;
 
@@ -24,6 +25,12 @@ pub struct Key<T> {
     dtor_running: Cell<bool>,
 }
 
+impl<T> fmt::Debug for Key<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Key { .. }")
+    }
+}
+
 unsafe impl<T> ::marker::Sync for Key<T> { }
 
 impl<T> Key<T> {

src/libstd/sys/unix/fd.rs

@@ -18,6 +18,7 @@
 use sys_common::AsInner;
 use sys_common::io::read_to_end_uninitialized;
 
+#[derive(Debug)]
 pub struct FileDesc {
     fd: c_int,
 }

src/libstd/sys/unix/fs.rs

@@ -66,7 +66,7 @@ pub struct DirEntry {
     name: Box<[u8]>
 }
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct OpenOptions {
     // generic
     read: bool,
@@ -86,6 +86,7 @@ pub struct FilePermissions { mode: mode_t }
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub struct FileType { mode: mode_t }
 
+#[derive(Debug)]
 pub struct DirBuilder { mode: mode_t }
 
 impl FileAttr {

src/libstd/sys/windows/fs.rs

@@ -58,7 +58,7 @@ pub struct DirEntry {
     data: c::WIN32_FIND_DATAW,
 }
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct OpenOptions {
     // generic
     read: bool,
@@ -79,6 +79,7 @@ pub struct OpenOptions {
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct FilePermissions { attrs: c::DWORD }
 
+#[derive(Debug)]
 pub struct DirBuilder;
 
 impl fmt::Debug for ReadDir {

src/libstd/thread/local.rs

@@ -13,6 +13,7 @@
 #![unstable(feature = "thread_local_internals", issue = "0")]
 
 use cell::UnsafeCell;
+use fmt;
 use mem;
 
 /// A thread local storage key which owns its contents.
@@ -98,6 +99,13 @@ pub struct LocalKey<T: 'static> {
     init: fn() -> T,
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<T: 'static> fmt::Debug for LocalKey<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("LocalKey { .. }")
+    }
+}
+
 /// Declare a new thread local storage key of type `std::thread::LocalKey`.
 ///
 /// # Syntax
@@ -184,7 +192,7 @@ fn __getit() -> $crate::option::Option<
 #[unstable(feature = "thread_local_state",
            reason = "state querying was recently added",
            issue = "27716")]
-#[derive(Eq, PartialEq, Copy, Clone)]
+#[derive(Debug, Eq, PartialEq, Copy, Clone)]
 pub enum LocalKeyState {
     /// All keys are in this state whenever a thread starts. Keys will
     /// transition to the `Valid` state once the first call to `with` happens
@@ -313,6 +321,7 @@ pub fn state(&'static self) -> LocalKeyState {
 #[doc(hidden)]
 pub mod os {
     use cell::{Cell, UnsafeCell};
+    use fmt;
     use marker;
     use ptr;
     use sys_common::thread_local::StaticKey as OsStaticKey;
@@ -323,6 +332,13 @@ pub struct Key<T> {
         marker: marker::PhantomData<Cell<T>>,
     }
 
+    #[stable(feature = "std_debug", since = "1.15.0")]
+    impl<T> fmt::Debug for Key<T> {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            f.pad("Key { .. }")
+        }
+    }
+
     unsafe impl<T> ::marker::Sync for Key<T> { }
 
     struct Value<T: 'static> {

src/libstd/thread/mod.rs

@@ -203,6 +203,7 @@
 /// Thread configuration. Provides detailed control over the properties
 /// and behavior of new threads.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct Builder {
     // A name for the thread-to-be, for identification in panic messages
     name: Option<String>,
@@ -573,6 +574,13 @@ fn new() -> ThreadId {
     }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for ThreadId {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("ThreadId { .. }")
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Thread
 ////////////////////////////////////////////////////////////////////////////////
@@ -788,6 +796,13 @@ impl<T> IntoInner<imp::Thread> for JoinHandle<T> {
     fn into_inner(self) -> imp::Thread { self.0.native.unwrap() }
 }
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl<T> fmt::Debug for JoinHandle<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("JoinHandle { .. }")
+    }
+}
+
 fn _assert_sync_and_send() {
     fn _assert_both<T: Send + Sync>() {}
     _assert_both::<JoinHandle<()>>();