Auto merge of #100869 - nnethercote:replace-ThinVec, r=spastorino

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.

r? `@spastorino`

2 files changed, 12 insertions, 7 deletions

diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
index b564f4ad92c..f353ee6df9b 100644
--- a/compiler/rustc_parse/src/parser/attr_wrapper.rs
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -355,7 +355,7 @@ impl<'a> Parser<'a> {
             && matches!(self.capture_state.capturing, Capturing::Yes)
             && has_cfg_or_cfg_attr(final_attrs)
         {
-            let attr_data = AttributesData { attrs: final_attrs.to_vec().into(), tokens };
+            let attr_data = AttributesData { attrs: final_attrs.iter().cloned().collect(), tokens };
 
             // Replace the entire AST node that we just parsed, including attributes,
             // with a `FlatToken::AttrTarget`. If this AST node is inside an item
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index be00e57b932..d4828a20120 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -944,13 +944,18 @@ impl<'a> Parser<'a> {
         // Stitch the list of outer attributes onto the return value.
         // A little bit ugly, but the best way given the current code
         // structure
-        self.parse_dot_or_call_expr_with_(e0, lo).map(|expr| {
-            expr.map(|mut expr| {
-                attrs.extend(expr.attrs);
-                expr.attrs = attrs;
-                expr
+        let res = self.parse_dot_or_call_expr_with_(e0, lo);
+        if attrs.is_empty() {
+            res
+        } else {
+            res.map(|expr| {
+                expr.map(|mut expr| {
+                    attrs.extend(expr.attrs);
+                    expr.attrs = attrs;
+                    expr
+                })
             })
-        })
+        }
     }
 
     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {