Rollup merge of #26678 - bluss:doc-fmt, r=steveklabnik

fmt: Update docs and mention :#? pretty-printing

Expose `:#?` well in the docs for fmt and Debug itself. Also update some out of date information and fix formatting in `std::fmt` docs.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index cbbb186af76..35dea6d15f0 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -267,7 +267,7 @@ impl<'a> Display for Arguments<'a> {
     }
 }
 
-/// Format trait for the `:?` format. Useful for debugging, all types
+/// Format trait for the `?` character. Useful for debugging, all types
 /// should implement this.
 ///
 /// Generally speaking, you should just `derive` a `Debug` implementation.
@@ -312,6 +312,9 @@ impl<'a> Display for Arguments<'a> {
 /// There are a number of `debug_*` methods on `Formatter` to help you with manual
 /// implementations, such as [`debug_struct`][debug_struct].
 ///
+/// `Debug` implementations using either `derive` or the debug builder API
+/// on `Formatter` support pretty printing using the alternate flag: `{:#?}`.
+///
 /// [debug_struct]: ../std/fmt/struct.Formatter.html#method.debug_struct
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented = "`{Self}` cannot be formatted using `:?`; if it is \