Replace rustc_data_structures::thin_vec::ThinVec with thin_vec::ThinVec.

`rustc_data_structures::thin_vec::ThinVec` looks like this:
```
pub struct ThinVec<T>(Option<Box<Vec<T>>>);
```
It's just a zero word if the vector is empty, but requires two
allocations if it is non-empty. So it's only usable in cases where the
vector is empty most of the time.

This commit removes it in favour of `thin_vec::ThinVec`, which is also
word-sized, but stores the length and capacity in the same allocation as
the elements. It's good in a wider variety of situation, e.g. in enum
variants where the vector is usually/always non-empty.

The commit also:
- Sorts some `Cargo.toml` dependency lists, to make additions easier.
- Sorts some `use` item lists, to make additions easier.
- Changes `clean_trait_ref_with_bindings` to take a
  `ThinVec<TypeBinding>` rather than a `&[TypeBinding]`, because this
  avoid some unnecessary allocations.

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -13,6 +13,7 @@ use rustc_span::{
     symbol::{sym, Ident, Symbol},
     Span,
 };
+use thin_vec::thin_vec;
 
 pub(super) struct Context<'cx, 'a> {
     // An optimization.
@@ -116,11 +117,10 @@ impl<'cx, 'a> Context<'cx, 'a> {
             self.cx.item(
                 self.span,
                 Ident::empty(),
-                vec![self.cx.attribute(attr::mk_list_item(
+                thin_vec![self.cx.attribute(attr::mk_list_item(
                     Ident::new(sym::allow, self.span),
                     vec![attr::mk_nested_word_item(Ident::new(sym::unused_imports, self.span))],
-                ))]
-                .into(),
+                ))],
                 ItemKind::Use(UseTree {
                     prefix: self.cx.path(self.span, self.cx.std_path(&[sym::asserting])),
                     kind: UseTreeKind::Nested(vec![

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,12 +1,12 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::path_std;
-
 use rustc_ast::{self as ast, Generics, ItemKind, MetaItem, VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 pub fn expand_deriving_clone(
     cx: &mut ExtCtxt<'_>,
@@ -68,7 +68,7 @@ pub fn expand_deriving_clone(
     }
 
     let inline = cx.meta_word(span, sym::inline);
-    let attrs = vec![cx.attribute(inline)].into();
+    let attrs = thin_vec![cx.attribute(inline)];
     let trait_def = TraitDef {
         span,
         path: path_std!(clone::Clone),

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -7,6 +7,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 pub fn expand_deriving_eq(
     cx: &mut ExtCtxt<'_>,
@@ -20,7 +21,7 @@ pub fn expand_deriving_eq(
     let hidden = rustc_ast::attr::mk_nested_word_item(Ident::new(sym::hidden, span));
     let doc = rustc_ast::attr::mk_list_item(Ident::new(sym::doc, span), vec![hidden]);
     let no_coverage = cx.meta_word(span, sym::no_coverage);
-    let attrs = vec![cx.attribute(inline), cx.attribute(doc), cx.attribute(no_coverage)].into();
+    let attrs = thin_vec![cx.attribute(inline), cx.attribute(doc), cx.attribute(no_coverage)];
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::Eq),

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,11 +1,11 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::path_std;
-
 use rustc_ast::MetaItem;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 pub fn expand_deriving_ord(
     cx: &mut ExtCtxt<'_>,
@@ -15,7 +15,7 @@ pub fn expand_deriving_ord(
     push: &mut dyn FnMut(Annotatable),
 ) {
     let inline = cx.meta_word(span, sym::inline);
-    let attrs = vec![cx.attribute(inline)].into();
+    let attrs = thin_vec![cx.attribute(inline)];
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::Ord),

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,12 +1,12 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::{path_local, path_std};
-
 use rustc_ast::ptr::P;
 use rustc_ast::{BinOpKind, BorrowKind, Expr, ExprKind, MetaItem, Mutability};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 pub fn expand_deriving_partial_eq(
     cx: &mut ExtCtxt<'_>,
@@ -68,7 +68,7 @@ pub fn expand_deriving_partial_eq(
     // No need to generate `ne`, the default suffices, and not generating it is
     // faster.
     let inline = cx.meta_word(span, sym::inline);
-    let attrs = vec![cx.attribute(inline)].into();
+    let attrs = thin_vec![cx.attribute(inline)];
     let methods = vec![MethodDef {
         name: sym::eq,
         generics: Bounds::empty(),

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,11 +1,11 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::{path_std, pathvec_std};
-
 use rustc_ast::MetaItem;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 pub fn expand_deriving_partial_ord(
     cx: &mut ExtCtxt<'_>,
@@ -19,7 +19,7 @@ pub fn expand_deriving_partial_ord(
         Path(Path::new_(pathvec_std!(option::Option), vec![Box::new(ordering_ty)], PathKind::Std));
 
     let inline = cx.meta_word(span, sym::inline);
-    let attrs = vec![cx.attribute(inline)].into();
+    let attrs = thin_vec![cx.attribute(inline)];
 
     let partial_cmp_def = MethodDef {
         name: sym::partial_cmp,

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,6 +1,5 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
-
 use rustc_ast as ast;
 use rustc_ast::{walk_list, EnumDef, VariantData};
 use rustc_errors::Applicability;
@@ -9,6 +8,7 @@ use rustc_span::symbol::Ident;
 use rustc_span::symbol::{kw, sym};
 use rustc_span::Span;
 use smallvec::SmallVec;
+use thin_vec::thin_vec;
 
 pub fn expand_deriving_default(
     cx: &mut ExtCtxt<'_>,
@@ -20,7 +20,7 @@ pub fn expand_deriving_default(
     item.visit_with(&mut DetectNonVariantDefaultAttr { cx });
 
     let inline = cx.meta_word(span, sym::inline);
-    let attrs = vec![cx.attribute(inline)].into();
+    let attrs = thin_vec![cx.attribute(inline)];
     let trait_def = TraitDef {
         span,
         path: Path::new(vec![kw::Default, sym::Default]),

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -162,10 +162,7 @@
 pub use StaticFields::*;
 pub use SubstructureFields::*;
 
-use std::cell::RefCell;
-use std::iter;
-use std::vec;
-
+use crate::deriving;
 use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, EnumDef, Expr, Generics, PatKind};
 use rustc_ast::{GenericArg, GenericParamKind, VariantData};
@@ -173,11 +170,12 @@ use rustc_attr as attr;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
-
+use std::cell::RefCell;
+use std::iter;
+use std::vec;
+use thin_vec::thin_vec;
 use ty::{Bounds, Path, Ref, Self_, Ty};
 
-use crate::deriving;
-
 pub mod ty;
 
 pub struct TraitDef<'a> {
@@ -716,7 +714,7 @@ impl<'a> TraitDef<'a> {
         let self_type = cx.ty_path(path);
 
         let attr = cx.attribute(cx.meta_word(self.span, sym::automatically_derived));
-        let attrs = vec![attr].into();
+        let attrs = thin_vec![attr];
         let opt_trait_ref = Some(trait_ref);
 
         cx.item(

compiler/rustc_builtin_macros/src/global_allocator.rs

@@ -9,6 +9,7 @@ use rustc_ast::{Fn, ItemKind, Mutability, Stmt, Ty, TyKind, Unsafe};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 pub fn expand(
     ecx: &mut ExtCtxt<'_>,
@@ -116,7 +117,7 @@ impl AllocFnFactory<'_, '_> {
     fn attrs(&self) -> AttrVec {
         let special = sym::rustc_std_internal_symbol;
         let special = self.cx.meta_word(self.span, special);
-        vec![self.cx.attribute(special)].into()
+        thin_vec![self.cx.attribute(special)]
     }
 
     fn arg_ty(

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -6,6 +6,7 @@ use rustc_span::edition::Edition::*;
 use rustc_span::hygiene::AstPass;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::DUMMY_SP;
+use thin_vec::thin_vec;
 
 pub fn inject(
     mut krate: ast::Crate,
@@ -51,7 +52,7 @@ pub fn inject(
             cx.item(
                 span,
                 ident,
-                vec![cx.attribute(cx.meta_word(span, sym::macro_use))].into(),
+                thin_vec![cx.attribute(cx.meta_word(span, sym::macro_use))],
                 ast::ItemKind::ExternCrate(None),
             ),
         );
@@ -78,7 +79,7 @@ pub fn inject(
     let use_item = cx.item(
         span,
         Ident::empty(),
-        vec![cx.attribute(cx.meta_word(span, sym::prelude_import))].into(),
+        thin_vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
         ast::ItemKind::Use(ast::UseTree {
             prefix: cx.path(span, import_path),
             kind: ast::UseTreeKind::Glob,

compiler/rustc_builtin_macros/src/test.rs

@@ -1,7 +1,6 @@
 /// The expansion from a test function to the appropriate test struct for libtest
 /// Ideally, this code would be in libtest but for efficiency and error messages it lives here.
 use crate::util::{check_builtin_macro_attribute, warn_on_duplicate_attribute};
-
 use rustc_ast as ast;
 use rustc_ast::attr;
 use rustc_ast::ptr::P;
@@ -11,8 +10,8 @@ use rustc_expand::base::*;
 use rustc_session::Session;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
-
 use std::iter;
+use thin_vec::thin_vec;
 
 // #[test_case] is used by custom test authors to mark tests
 // When building for test, it needs to make the item public and gensym the name
@@ -219,7 +218,7 @@ pub fn expand_test_or_bench(
     let mut test_const = cx.item(
         sp,
         Ident::new(item.ident.name, sp),
-        vec![
+        thin_vec![
             // #[cfg(test)]
             cx.attribute(attr::mk_list_item(
                 Ident::new(sym::cfg, attr_sp),
@@ -227,8 +226,7 @@ pub fn expand_test_or_bench(
             )),
             // #[rustc_test_marker]
             cx.attribute(cx.meta_word(attr_sp, sym::rustc_test_marker)),
-        ]
-        .into(),
+        ],
         // const $ident: test::TestDescAndFn =
         ast::ItemKind::Const(
             ast::Defaultness::Final,

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -14,6 +14,7 @@ use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::PanicStrategy;
 use smallvec::{smallvec, SmallVec};
+use thin_vec::thin_vec;
 use tracing::debug;
 
 use std::{iter, mem};
@@ -335,7 +336,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
 
     let main = P(ast::Item {
         ident: main_id,
-        attrs: vec![main_attr].into(),
+        attrs: thin_vec![main_attr],
         id: ast::DUMMY_NODE_ID,
         kind: main,
         vis: ast::Visibility { span: sp, kind: ast::VisibilityKind::Public, tokens: None },