3 files changed, 86 insertions, 6 deletions

diff --git a/crates/assists/src/handlers/merge_imports.rs b/crates/assists/src/handlers/merge_imports.rs
index fe33cee53..fd9c9e03c 100644
--- a/crates/assists/src/handlers/merge_imports.rs
+++ b/crates/assists/src/handlers/merge_imports.rs
@@ -73,6 +73,20 @@ mod tests {
     use super::*;
 
     #[test]
+    fn test_merge_equal() {
+        check_assist(
+            merge_imports,
+            r"
+use std::fmt<|>::{Display, Debug};
+use std::fmt::{Display, Debug};
+",
+            r"
+use std::fmt::{Debug, Display};
+",
+        )
+    }
+
+    #[test]
     fn test_merge_first() {
         check_assist(
             merge_imports,
diff --git a/crates/assists/src/handlers/replace_qualified_name_with_use.rs b/crates/assists/src/handlers/replace_qualified_name_with_use.rs
index 74afc123b..c50bc7604 100644
--- a/crates/assists/src/handlers/replace_qualified_name_with_use.rs
+++ b/crates/assists/src/handlers/replace_qualified_name_with_use.rs
@@ -124,6 +124,23 @@ mod tests {
     use super::*;
 
     #[test]
+    fn test_replace_already_imported() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"use std::fs;
+
+fn main() {
+    std::f<|>s::Path
+}",
+            r"use std::fs;
+
+fn main() {
+    fs::Path
+}",
+        )
+    }
+
+    #[test]
     fn test_replace_add_use_no_anchor() {
         check_assist(
             replace_qualified_name_with_use,
@@ -393,7 +410,7 @@ impl std::fmt::Display<|> for Foo {
 }
 ",
             r"
-use std::fmt::{Display, nested::Debug};
+use std::fmt::{nested::Debug, Display};
 
 impl Display for Foo {
 }
diff --git a/crates/assists/src/utils/insert_use.rs b/crates/assists/src/utils/insert_use.rs
index f6025c99a..409985b3b 100644
--- a/crates/assists/src/utils/insert_use.rs
+++ b/crates/assists/src/utils/insert_use.rs
@@ -173,8 +173,15 @@ pub(crate) fn try_merge_trees(
     let rhs_path = rhs.path()?;
 
     let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
-    let lhs = lhs.split_prefix(&lhs_prefix);
-    let rhs = rhs.split_prefix(&rhs_prefix);
+    let (lhs, rhs) = if is_simple_path(lhs)
+        && is_simple_path(rhs)
+        && lhs_path == lhs_prefix
+        && rhs_path == rhs_prefix
+    {
+        (lhs.clone(), rhs.clone())
+    } else {
+        (lhs.split_prefix(&lhs_prefix), rhs.split_prefix(&rhs_prefix))
+    };
     recursive_merge(&lhs, &rhs, merge)
 }
 
@@ -200,7 +207,18 @@ fn recursive_merge(
             return None;
         }
         let rhs_path = rhs_t.path();
-        match use_trees.binary_search_by(|p| path_cmp_bin_search(p.path(), rhs_path.clone())) {
+        match use_trees.binary_search_by(|lhs_t| {
+            let (lhs_t, rhs_t) = match lhs_t
+                .path()
+                .zip(rhs_path.clone())
+                .and_then(|(lhs, rhs)| common_prefix(&lhs, &rhs))
+            {
+                Some((lhs_p, rhs_p)) => (lhs_t.split_prefix(&lhs_p), rhs_t.split_prefix(&rhs_p)),
+                None => (lhs_t.clone(), rhs_t.clone()),
+            };
+
+            path_cmp_bin_search(lhs_t.path(), rhs_t.path())
+        }) {
             Ok(idx) => {
                 let lhs_t = &mut use_trees[idx];
                 let lhs_path = lhs_t.path()?;
@@ -239,6 +257,10 @@ fn recursive_merge(
                         use_trees.insert(idx, make::glob_use_tree());
                         continue;
                     }
+
+                    if lhs_t.use_tree_list().is_none() && rhs_t.use_tree_list().is_none() {
+                        continue;
+                    }
                 }
                 let lhs = lhs_t.split_prefix(&lhs_prefix);
                 let rhs = rhs_t.split_prefix(&rhs_prefix);
@@ -284,6 +306,10 @@ fn common_prefix(lhs: &ast::Path, rhs: &ast::Path) -> Option<(ast::Path, ast::Pa
     }
 }
 
+fn is_simple_path(use_tree: &ast::UseTree) -> bool {
+    use_tree.use_tree_list().is_none() && use_tree.star_token().is_none()
+}
+
 fn path_is_self(path: &ast::Path) -> bool {
     path.segment().and_then(|seg| seg.self_token()).is_some() && path.qualifier().is_none()
 }
@@ -327,11 +353,11 @@ fn path_cmp_for_sort(a: Option<ast::Path>, b: Option<ast::Path>) -> Ordering {
 
 /// Path comparison func for binary searching for merging.
 fn path_cmp_bin_search(lhs: Option<ast::Path>, rhs: Option<ast::Path>) -> Ordering {
-    match (lhs, rhs) {
+    match (lhs.and_then(|path| path.segment()), rhs.and_then(|path| path.segment())) {
         (None, None) => Ordering::Equal,
         (None, Some(_)) => Ordering::Less,
         (Some(_), None) => Ordering::Greater,
-        (Some(ref a), Some(ref b)) => path_cmp_short(a, b),
+        (Some(ref a), Some(ref b)) => path_segment_cmp(a, b),
     }
 }
 
@@ -513,6 +539,11 @@ mod tests {
     use test_utils::assert_eq_text;
 
     #[test]
+    fn insert_existing() {
+        check_full("std::fs", "use std::fs;", "use std::fs;")
+    }
+
+    #[test]
     fn insert_start() {
         check_none(
             "std::bar::AA",
@@ -802,6 +833,24 @@ use std::foo::bar::{Qux, quux::{Fez, Fizz}};",
     }
 
     #[test]
+    fn merge_groups_full_nested_long() {
+        check_full(
+            "std::foo::bar::Baz",
+            r"use std::{foo::bar::Qux};",
+            r"use std::{foo::bar::{Baz, Qux}};",
+        );
+    }
+
+    #[test]
+    fn merge_groups_last_nested_long() {
+        check_full(
+            "std::foo::bar::Baz",
+            r"use std::{foo::bar::Qux};",
+            r"use std::{foo::bar::{Baz, Qux}};",
+        );
+    }
+
+    #[test]
     fn merge_groups_skip_pub() {
         check_full(
             "std::io",