std: Rename Show/String to Debug/Display

This commit is an implementation of [RFC 565][rfc] which is a stabilization of
the `std::fmt` module and the implementations of various formatting traits.
Specifically, the following changes were performed:

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0565-show-string-guidelines.md

* The `Show` trait is now deprecated, it was renamed to `Debug`
* The `String` trait is now deprecated, it was renamed to `Display`
* Many `Debug` and `Display` implementations were audited in accordance with the
  RFC and audited implementations now have the `#[stable]` attribute
  * Integers and floats no longer print a suffix
  * Smart pointers no longer print details that they are a smart pointer
  * Paths with `Debug` are now quoted and escape characters
* The `unwrap` methods on `Result` now require `Display` instead of `Debug`
* The `Error` trait no longer has a `detail` method and now requires that
  `Display` must be implemented. With the loss of `String`, this has moved into
  libcore.
* `impl<E: Error> FromError<E> for Box<Error>` now exists
* `derive(Show)` has been renamed to `derive(Debug)`. This is not currently
  warned about due to warnings being emitted on stage1+

While backwards compatibility is attempted to be maintained with a blanket
implementation of `Display` for the old `String` trait (and the same for
`Show`/`Debug`) this is still a breaking change due to primitives no longer
implementing `String` as well as modifications such as `unwrap` and the `Error`
trait. Most code is fairly straightforward to update with a rename or tweaks of
method calls.

[breaking-change]
Closes #21436

2 files changed, 9 insertions, 9 deletions

diff --git a/src/libgraphviz/lib.rs b/src/libgraphviz/lib.rs
index 2d7d88f0f35..0ed32b7bf4f 100644
--- a/src/libgraphviz/lib.rs
+++ b/src/libgraphviz/lib.rs
@@ -358,19 +358,19 @@ impl<'a> Id<'a> {
     ///
     /// Passing an invalid string (containing spaces, brackets,
     /// quotes, ...) will return an empty `Err` value.
-    pub fn new<Name: IntoCow<'a, String, str>>(name: Name) -> Result<Id<'a>, ()> {
+    pub fn new<Name: IntoCow<'a, String, str>>(name: Name) -> Option<Id<'a>> {
         let name = name.into_cow();
         {
             let mut chars = name.chars();
             match chars.next() {
                 Some(c) if is_letter_or_underscore(c) => { ; },
-                _ => return Err(())
+                _ => return None
             }
             if !chars.all(is_constituent) {
-                return Err(());
+                return None
             }
         }
-        return Ok(Id{ name: name });
+        return Some(Id{ name: name });
 
         fn is_letter_or_underscore(c: char) -> bool {
             in_range('a', c, 'z') || in_range('A', c, 'Z') || c == '_'
@@ -874,8 +874,8 @@ r#"digraph syntax_tree {
     fn simple_id_construction() {
         let id1 = Id::new("hello");
         match id1 {
-            Ok(_) => {;},
-            Err(_) => panic!("'hello' is not a valid value for id anymore")
+            Some(_) => {;},
+            None => panic!("'hello' is not a valid value for id anymore")
         }
     }
 
@@ -883,8 +883,8 @@ r#"digraph syntax_tree {
     fn badly_formatted_id() {
         let id2 = Id::new("Weird { struct : ure } !!!");
         match id2 {
-            Ok(_) => panic!("graphviz id suddenly allows spaces, brackets and stuff"),
-            Err(_) => {;}
+            Some(_) => panic!("graphviz id suddenly allows spaces, brackets and stuff"),
+            None => {;}
         }
     }
 }
diff --git a/src/libgraphviz/maybe_owned_vec.rs b/src/libgraphviz/maybe_owned_vec.rs
index 567fe04c5af..4e6437a5e76 100644
--- a/src/libgraphviz/maybe_owned_vec.rs
+++ b/src/libgraphviz/maybe_owned_vec.rs
@@ -124,7 +124,7 @@ impl<'a,T> FromIterator<T> for MaybeOwnedVector<'a,T> {
     }
 }
 
-impl<'a,T:fmt::Show> fmt::Show for MaybeOwnedVector<'a,T> {
+impl<'a,T:fmt::Debug> fmt::Debug for MaybeOwnedVector<'a,T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         self.as_slice().fmt(f)
     }