Auto merge of #125443 - nnethercote:rustfmt-use-decls, r=lcnr,cuviper,GuillaumeGomez

rustfmt `use` declarations

This PR implements https://github.com/rust-lang/compiler-team/issues/750, which changes how `use` declarations are formatted by adding these options to `rustfmt.toml`:
```
group_imports = "StdExternalCrate"
imports_granularity = "Module"
```

r? `@ghost`

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/rustc_serialize/src/serialize.rs b/compiler/rustc_serialize/src/serialize.rs
index c84bb26735c..2d37f5bdab8 100644
--- a/compiler/rustc_serialize/src/serialize.rs
+++ b/compiler/rustc_serialize/src/serialize.rs
@@ -1,6 +1,5 @@
 //! Support code for encoding and decoding types.
 
-use smallvec::{Array, SmallVec};
 use std::borrow::Cow;
 use std::cell::{Cell, RefCell};
 use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet, VecDeque};
@@ -10,6 +9,8 @@ use std::num::NonZero;
 use std::path;
 use std::rc::Rc;
 use std::sync::Arc;
+
+use smallvec::{Array, SmallVec};
 use thin_vec::ThinVec;
 
 /// A byte that [cannot occur in UTF8 sequences][utf8]. Used to mark the end of a string.