Fix import suggestion error when failed not from starting

compiler/rustc_resolve/src/diagnostics.rs

@@ -1987,10 +1987,20 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             candidates
                 .sort_by_cached_key(|c| (c.path.segments.len(), pprust::path_to_string(&c.path)));
             if let Some(candidate) = candidates.get(0) {
+                let path = {
+                    // remove the common prefix of the path
+                    let start_index = (0..failed_segment_idx)
+                        .find(|&i| path[i].ident != candidate.path.segments[i].ident)
+                        .unwrap_or_default();
+                    let segments = (start_index..=failed_segment_idx)
+                        .map(|s| candidate.path.segments[s].clone())
+                        .collect();
+                    Path { segments, span: Span::default(), tokens: None }
+                };
                 (
                     String::from("unresolved import"),
                     Some((
-                        vec![(ident.span, pprust::path_to_string(&candidate.path))],
+                        vec![(ident.span, pprust::path_to_string(&path))],
                         String::from("a similar path exists"),
                         Applicability::MaybeIncorrect,
                     )),

tests/ui/imports/suggest-import-issue-120074.rs

@@ -0,0 +1,11 @@
+pub mod foo {
+    pub mod bar {
+        pub fn do_the_thing() -> usize {
+            42
+        }
+    }
+}
+
+fn main() {
+    println!("Hello, {}!", crate::bar::do_the_thing); //~ ERROR failed to resolve: unresolved import
+}

tests/ui/imports/suggest-import-issue-120074.stderr

@@ -0,0 +1,23 @@
+error[E0433]: failed to resolve: unresolved import
+  --> $DIR/suggest-import-issue-120074.rs:10:35
+   |
+LL |     println!("Hello, {}!", crate::bar::do_the_thing);
+   |                                   ^^^ unresolved import
+   |
+help: a similar path exists
+   |
+LL |     println!("Hello, {}!", crate::foo::bar::do_the_thing);
+   |                                   ~~~~~~~~
+help: consider importing this module
+   |
+LL + use foo::bar;
+   |
+help: if you import `bar`, refer to it directly
+   |
+LL -     println!("Hello, {}!", crate::bar::do_the_thing);
+LL +     println!("Hello, {}!", bar::do_the_thing);
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0433`.