Rollup merge of #123344 - pietroalbini:pa-unused-imports, r=Nilstrieb

Remove braces when fixing a nested use tree into a single item

[Back in 2019](https://github.com/rust-lang/rust/pull/56645) I added rustfix support for the `unused_imports` lint, to automatically remove them when running `cargo fix`. For the most part this worked great, but when removing all but one childs of a nested use tree it turned `use foo::{Unused, Used}` into `use foo::{Used}`. This is slightly annoying, because it then requires you to run `rustfmt` to get `use foo::Used`.

This PR automatically removes braces and the surrouding whitespace when all but one child of a nested use tree are unused. To get it done I had to add the span of the nested use tree to the AST, and refactor a bit the code I wrote back then.

A thing I noticed is, there doesn't seem to be any `//@ run-rustfix` test for fixing the `unused_imports` lint. I created a test in `tests/suggestions` (is that the right directory?) that for now tests just what I added in the PR. I can followup in a separate PR to add more tests for fixing `unused_lints`.

This PR is best reviewed commit-by-commit.

clippy_lints/src/single_component_path_imports.rs

@@ -201,8 +201,8 @@ impl SingleComponentPathImports {
 
                 if segments.is_empty() {
                     // keep track of `use {some_module, some_other_module};` usages
-                    if let UseTreeKind::Nested(trees) = &use_tree.kind {
+                    if let UseTreeKind::Nested { items, .. } = &use_tree.kind {
-                        for tree in trees {
+                        for tree in items {
                             let segments = &tree.0.prefix.segments;
                             if segments.len() == 1 {
                                 if let UseTreeKind::Simple(None) = tree.0.kind {
@@ -229,8 +229,8 @@ impl SingleComponentPathImports {
                         }
 
                         // nested case such as `use self::{module1::Struct1, module2::Struct2}`
-                        if let UseTreeKind::Nested(trees) = &use_tree.kind {
+                        if let UseTreeKind::Nested { items, .. } = &use_tree.kind {
-                            for tree in trees {
+                            for tree in items {
                                 let segments = &tree.0.prefix.segments;
                                 if !segments.is_empty() {
                                     imports_reused_with_self.push(segments[0].ident.name);

clippy_lints/src/unnecessary_self_imports.rs

@@ -36,8 +36,8 @@ declare_lint_pass!(UnnecessarySelfImports => [UNNECESSARY_SELF_IMPORTS]);
 impl EarlyLintPass for UnnecessarySelfImports {
     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
         if let ItemKind::Use(use_tree) = &item.kind
-            && let UseTreeKind::Nested(nodes) = &use_tree.kind
+            && let UseTreeKind::Nested { items, .. } = &use_tree.kind
-            && let [(self_tree, _)] = &**nodes
+            && let [(self_tree, _)] = &**items
             && let [self_seg] = &*self_tree.prefix.segments
             && self_seg.ident.name == kw::SelfLower
             && let Some(last_segment) = use_tree.prefix.segments.last()

clippy_lints/src/unsafe_removed_from_name.rs

@@ -49,8 +49,8 @@ fn check_use_tree(use_tree: &UseTree, cx: &EarlyContext<'_>, span: Span) {
             unsafe_to_safe_check(old_name, new_name, cx, span);
         },
         UseTreeKind::Simple(None) | UseTreeKind::Glob => {},
-        UseTreeKind::Nested(ref nested_use_tree) => {
+        UseTreeKind::Nested { ref items, .. } => {
-            for (use_tree, _) in nested_use_tree {
+            for (use_tree, _) in items {
                 check_use_tree(use_tree, cx, span);
             }
         },

clippy_utils/src/ast_utils.rs

@@ -648,7 +648,7 @@ pub fn eq_use_tree_kind(l: &UseTreeKind, r: &UseTreeKind) -> bool {
     match (l, r) {
         (Glob, Glob) => true,
         (Simple(l), Simple(r)) => both(l, r, |l, r| eq_id(*l, *r)),
-        (Nested(l), Nested(r)) => over(l, r, |(l, _), (r, _)| eq_use_tree(l, r)),
+        (Nested { items: l, .. }, Nested { items: r, .. }) => over(l, r, |(l, _), (r, _)| eq_use_tree(l, r)),
         _ => false,
     }
 }