Use fine grained component-wise span tracking in use trees

[oli-obk]

This often produces nicer spans and even doesn't need a Span field anymore (not that I expect the unused field to affect any perf, but still neat).

[rustbot]

The parser was modified, potentially altering the grammar of (stable) Rust
which would be a breaking change.

cc @fmease

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[rustbot]

r? @davidtwco

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[oli-obk]

These suggestions are now even more broken than before, but considering it was broken before, I think we should just leave it

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[TIMING:end] tool::ToolBuild { build_compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu, tool: "tidy", path: "src/tools/tidy", mode: ToolBootstrap, source_type: InTree, extra_features: [], allow_features: "", cargo_args: [], artifact_kind: Binary } -- 12.641
[TIMING:end] tool::Tidy { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu } -- 0.000
fmt check
Diff in /checkout/compiler/rustc_ast/src/ast.rs:3358:
             _ => panic!("`UseTree::ident` can only be used on a simple import"),
         }
     }
-    
+
     pub fn span(&self) -> Span {
         self.prefix.span.to(self.hi_span())
     }
Diff in /checkout/compiler/rustc_ast/src/ast.rs:3365:
-    
+
     pub fn hi_span(&self) -> Span {
         match self.kind {
             UseTreeKind::Simple(None) => self.prefix.span,
Diff in /checkout/compiler/rustc_resolve/src/check_unused.rs:309:
         }
         ast::UseTreeKind::Nested { items: ref nested, span: tree_span } => {
             if nested.is_empty() {
-                return UnusedSpanResult::Unused { spans: vec![use_tree.span()], remove: full_span };
+                return UnusedSpanResult::Unused {
+                    spans: vec![use_tree.span()],
+                    remove: full_span,
+                };
             }
 
             let mut unused_spans = Vec::new();
Diff in /checkout/compiler/rustc_resolve/src/check_unused.rs:379:
                 if used_children == 1 && !contains_self {
                     // Left brace, from the start of the nested group to the first item.
                     to_remove.push(
-                        tree_span.shrink_to_lo().to(nested.first().unwrap().0.prefix.span.shrink_to_lo()),
+                        tree_span.shrink_to_lo().to(nested
+                            .first()
+                            .unwrap()
+                            .0
+                            .prefix
+                            .span
+                            .shrink_to_lo()),
                     );
                     // Right brace, from the end of the last item to the end of the nested group.
                     to_remove.push(
Diff in /checkout/compiler/rustc_resolve/src/check_unused.rs:386:
-                        nested.last().unwrap().0.hi_span().shrink_to_hi().to(tree_span.shrink_to_hi()),
+                        nested
+                            .last()
+                            .unwrap()
+                            .0
+                            .hi_span()
+                            .shrink_to_hi()
+                            .to(tree_span.shrink_to_hi()),
                     );
                 }
 
Diff in /checkout/compiler/rustc_resolve/src/build_reduced_graph.rs:606:
             Some(seg) if !seg.ident.is_path_segment_keyword() && seg.ident.span.is_rust_2015() => {
                 Some(seg.ident.span.ctxt())
             }
-            None if let ast::UseTreeKind::Glob(span) = use_tree.kind && span.is_rust_2015() => Some(span.ctxt()),
+            None if let ast::UseTreeKind::Glob(span) = use_tree.kind
+                && span.is_rust_2015() =>
+            {
+                Some(span.ctxt())
+            }
             _ => None,
         }
         .map(|ctxt| {
fmt: checked 6742 files
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Build completed unsuccessfully in 0:00:45
  local time: Fri Mar 13 21:05:13 UTC 2026
  network time: Fri, 13 Mar 2026 21:05:13 GMT