Split out merge_imports module from helpers::insert_use

8 files changed, 344 insertions, 329 deletions

diff --git a/crates/ide_assists/src/handlers/merge_imports.rs b/crates/ide_assists/src/handlers/merge_imports.rs
index 8e0794218..add7b8e37 100644
--- a/crates/ide_assists/src/handlers/merge_imports.rs
+++ b/crates/ide_assists/src/handlers/merge_imports.rs
@@ -1,4 +1,4 @@
-use ide_db::helpers::insert_use::{try_merge_imports, try_merge_trees, MergeBehavior};
+use ide_db::helpers::merge_imports::{try_merge_imports, try_merge_trees, MergeBehavior};
 use syntax::{algo::neighbor, ast, ted, AstNode};
 
 use crate::{
diff --git a/crates/ide_assists/src/tests.rs b/crates/ide_assists/src/tests.rs
index 49533e7d2..6f4f97361 100644
--- a/crates/ide_assists/src/tests.rs
+++ b/crates/ide_assists/src/tests.rs
@@ -4,10 +4,7 @@ use expect_test::expect;
 use hir::Semantics;
 use ide_db::{
     base_db::{fixture::WithFixture, FileId, FileRange, SourceDatabaseExt},
-    helpers::{
-        insert_use::{InsertUseConfig, MergeBehavior},
-        SnippetCap,
-    },
+    helpers::{insert_use::InsertUseConfig, merge_imports::MergeBehavior, SnippetCap},
     source_change::FileSystemEdit,
     RootDatabase,
 };
diff --git a/crates/ide_completion/src/test_utils.rs b/crates/ide_completion/src/test_utils.rs
index 9da844031..c9857ec5f 100644
--- a/crates/ide_completion/src/test_utils.rs
+++ b/crates/ide_completion/src/test_utils.rs
@@ -3,10 +3,7 @@
 use hir::{PrefixKind, Semantics};
 use ide_db::{
     base_db::{fixture::ChangeFixture, FileLoader, FilePosition},
-    helpers::{
-        insert_use::{InsertUseConfig, MergeBehavior},
-        SnippetCap,
-    },
+    helpers::{insert_use::InsertUseConfig, merge_imports::MergeBehavior, SnippetCap},
     RootDatabase,
 };
 use itertools::Itertools;
diff --git a/crates/ide_db/src/helpers.rs b/crates/ide_db/src/helpers.rs
index 720de0d1f..21b48237a 100644
--- a/crates/ide_db/src/helpers.rs
+++ b/crates/ide_db/src/helpers.rs
@@ -1,6 +1,7 @@
 //! A module with ide helpers for high-level ide features.
-pub mod insert_use;
 pub mod import_assets;
+pub mod insert_use;
+pub mod merge_imports;
 pub mod rust_doc;
 
 use std::collections::VecDeque;
diff --git a/crates/ide_db/src/helpers/insert_use.rs b/crates/ide_db/src/helpers/insert_use.rs
index a43504a27..55cdc4da3 100644
--- a/crates/ide_db/src/helpers/insert_use.rs
+++ b/crates/ide_db/src/helpers/insert_use.rs
@@ -1,15 +1,17 @@
 //! Handle syntactic aspects of inserting a new `use`.
-use std::{cmp::Ordering, iter::successors};
+use std::cmp::Ordering;
 
 use hir::Semantics;
-use itertools::{EitherOrBoth, Itertools};
 use syntax::{
     algo,
-    ast::{self, edit::AstNodeEdit, make, AstNode, AttrsOwner, PathSegmentKind, VisibilityOwner},
+    ast::{self, make, AstNode, PathSegmentKind},
     ted, AstToken, Direction, NodeOrToken, SyntaxNode, SyntaxToken,
 };
 
-use crate::RootDatabase;
+use crate::{
+    helpers::merge_imports::{try_merge_imports, use_tree_path_cmp, MergeBehavior},
+    RootDatabase,
+};
 
 pub use hir::PrefixKind;
 
@@ -85,318 +87,6 @@ pub fn insert_use<'a>(scope: &ImportScope, path: ast::Path, cfg: InsertUseConfig
     insert_use_(scope, path, cfg.group, use_item);
 }
 
-fn eq_visibility(vis0: Option<ast::Visibility>, vis1: Option<ast::Visibility>) -> bool {
-    match (vis0, vis1) {
-        (None, None) => true,
-        // FIXME: Don't use the string representation to check for equality
-        // spaces inside of the node would break this comparison
-        (Some(vis0), Some(vis1)) => vis0.to_string() == vis1.to_string(),
-        _ => false,
-    }
-}
-
-fn eq_attrs(
-    attrs0: impl Iterator<Item = ast::Attr>,
-    attrs1: impl Iterator<Item = ast::Attr>,
-) -> bool {
-    let attrs0 = attrs0.map(|attr| attr.to_string());
-    let attrs1 = attrs1.map(|attr| attr.to_string());
-    attrs0.eq(attrs1)
-}
-
-pub fn try_merge_imports(
-    lhs: &ast::Use,
-    rhs: &ast::Use,
-    merge_behavior: MergeBehavior,
-) -> Option<ast::Use> {
-    // don't merge imports with different visibilities
-    if !eq_visibility(lhs.visibility(), rhs.visibility()) {
-        return None;
-    }
-    if !eq_attrs(lhs.attrs(), rhs.attrs()) {
-        return None;
-    }
-
-    let lhs_tree = lhs.use_tree()?;
-    let rhs_tree = rhs.use_tree()?;
-    let merged = try_merge_trees(&lhs_tree, &rhs_tree, merge_behavior)?;
-    Some(lhs.with_use_tree(merged).clone_for_update())
-}
-
-pub fn try_merge_trees(
-    lhs: &ast::UseTree,
-    rhs: &ast::UseTree,
-    merge: MergeBehavior,
-) -> Option<ast::UseTree> {
-    let lhs_path = lhs.path()?;
-    let rhs_path = rhs.path()?;
-
-    let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
-    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)
-}
-
-/// Recursively "zips" together lhs and rhs.
-fn recursive_merge(
-    lhs: &ast::UseTree,
-    rhs: &ast::UseTree,
-    merge: MergeBehavior,
-) -> Option<ast::UseTree> {
-    let mut use_trees = lhs
-        .use_tree_list()
-        .into_iter()
-        .flat_map(|list| list.use_trees())
-        // we use Option here to early return from this function(this is not the same as a `filter` op)
-        .map(|tree| match merge.is_tree_allowed(&tree) {
-            true => Some(tree),
-            false => None,
-        })
-        .collect::<Option<Vec<_>>>()?;
-    use_trees.sort_unstable_by(|a, b| path_cmp_for_sort(a.path(), b.path()));
-    for rhs_t in rhs.use_tree_list().into_iter().flat_map(|list| list.use_trees()) {
-        if !merge.is_tree_allowed(&rhs_t) {
-            return None;
-        }
-        let rhs_path = rhs_t.path();
-        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()?;
-                let rhs_path = rhs_path?;
-                let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
-                if lhs_prefix == lhs_path && rhs_prefix == rhs_path {
-                    let tree_is_self = |tree: ast::UseTree| {
-                        tree.path().as_ref().map(path_is_self).unwrap_or(false)
-                    };
-                    // check if only one of the two trees has a tree list, and whether that then contains `self` or not.
-                    // If this is the case we can skip this iteration since the path without the list is already included in the other one via `self`
-                    let tree_contains_self = |tree: &ast::UseTree| {
-                        tree.use_tree_list()
-                            .map(|tree_list| tree_list.use_trees().any(tree_is_self))
-                            .unwrap_or(false)
-                    };
-                    match (tree_contains_self(&lhs_t), tree_contains_self(&rhs_t)) {
-                        (true, false) => continue,
-                        (false, true) => {
-                            *lhs_t = rhs_t;
-                            continue;
-                        }
-                        _ => (),
-                    }
-
-                    // glob imports arent part of the use-tree lists so we need to special handle them here as well
-                    // this special handling is only required for when we merge a module import into a glob import of said module
-                    // see the `merge_self_glob` or `merge_mod_into_glob` tests
-                    if lhs_t.star_token().is_some() || rhs_t.star_token().is_some() {
-                        *lhs_t = make::use_tree(
-                            make::path_unqualified(make::path_segment_self()),
-                            None,
-                            None,
-                            false,
-                        );
-                        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);
-                match recursive_merge(&lhs, &rhs, merge) {
-                    Some(use_tree) => use_trees[idx] = use_tree,
-                    None => return None,
-                }
-            }
-            Err(_)
-                if merge == MergeBehavior::Last
-                    && use_trees.len() > 0
-                    && rhs_t.use_tree_list().is_some() =>
-            {
-                return None
-            }
-            Err(idx) => {
-                use_trees.insert(idx, rhs_t);
-            }
-        }
-    }
-
-    Some(if let Some(old) = lhs.use_tree_list() {
-        lhs.replace_descendant(old, make::use_tree_list(use_trees)).clone_for_update()
-    } else {
-        lhs.clone()
-    })
-}
-
-/// Traverses both paths until they differ, returning the common prefix of both.
-fn common_prefix(lhs: &ast::Path, rhs: &ast::Path) -> Option<(ast::Path, ast::Path)> {
-    let mut res = None;
-    let mut lhs_curr = first_path(&lhs);
-    let mut rhs_curr = first_path(&rhs);
-    loop {
-        match (lhs_curr.segment(), rhs_curr.segment()) {
-            (Some(lhs), Some(rhs)) if lhs.syntax().text() == rhs.syntax().text() => (),
-            _ => break res,
-        }
-        res = Some((lhs_curr.clone(), rhs_curr.clone()));
-
-        match lhs_curr.parent_path().zip(rhs_curr.parent_path()) {
-            Some((lhs, rhs)) => {
-                lhs_curr = lhs;
-                rhs_curr = rhs;
-            }
-            _ => break res,
-        }
-    }
-}
-
-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()
-}
-
-#[inline]
-fn first_segment(path: &ast::Path) -> Option<ast::PathSegment> {
-    first_path(path).segment()
-}
-
-fn first_path(path: &ast::Path) -> ast::Path {
-    successors(Some(path.clone()), ast::Path::qualifier).last().unwrap()
-}
-
-fn segment_iter(path: &ast::Path) -> impl Iterator<Item = ast::PathSegment> + Clone {
-    // cant make use of SyntaxNode::siblings, because the returned Iterator is not clone
-    successors(first_segment(path), |p| p.parent_path().parent_path().and_then(|p| p.segment()))
-}
-
-fn path_len(path: ast::Path) -> usize {
-    segment_iter(&path).count()
-}
-
-/// Orders paths in the following way:
-/// the sole self token comes first, after that come uppercase identifiers, then lowercase identifiers
-// FIXME: rustfmt sorts lowercase idents before uppercase, in general we want to have the same ordering rustfmt has
-// which is `self` and `super` first, then identifier imports with lowercase ones first, then glob imports and at last list imports.
-// Example foo::{self, foo, baz, Baz, Qux, *, {Bar}}
-fn path_cmp_for_sort(a: Option<ast::Path>, b: Option<ast::Path>) -> Ordering {
-    match (a, b) {
-        (None, None) => Ordering::Equal,
-        (None, Some(_)) => Ordering::Less,
-        (Some(_), None) => Ordering::Greater,
-        (Some(ref a), Some(ref b)) => match (path_is_self(a), path_is_self(b)) {
-            (true, true) => Ordering::Equal,
-            (true, false) => Ordering::Less,
-            (false, true) => Ordering::Greater,
-            (false, false) => path_cmp_short(a, b),
-        },
-    }
-}
-
-/// Path comparison func for binary searching for merging.
-fn path_cmp_bin_search(lhs: Option<ast::Path>, rhs: Option<ast::Path>) -> Ordering {
-    match (lhs.as_ref().and_then(first_segment), rhs.as_ref().and_then(first_segment)) {
-        (None, None) => Ordering::Equal,
-        (None, Some(_)) => Ordering::Less,
-        (Some(_), None) => Ordering::Greater,
-        (Some(ref a), Some(ref b)) => path_segment_cmp(a, b),
-    }
-}
-
-/// Short circuiting comparison, if both paths are equal until one of them ends they are considered
-/// equal
-fn path_cmp_short(a: &ast::Path, b: &ast::Path) -> Ordering {
-    let a = segment_iter(a);
-    let b = segment_iter(b);
-    // cmp_by would be useful for us here but that is currently unstable
-    // cmp doesnt work due the lifetimes on text's return type
-    a.zip(b)
-        .find_map(|(a, b)| match path_segment_cmp(&a, &b) {
-            Ordering::Equal => None,
-            ord => Some(ord),
-        })
-        .unwrap_or(Ordering::Equal)
-}
-
-/// Compares to paths, if one ends earlier than the other the has_tl parameters decide which is
-/// greater as a a path that has a tree list should be greater, while one that just ends without
-/// a tree list should be considered less.
-fn use_tree_path_cmp(a: &ast::Path, a_has_tl: bool, b: &ast::Path, b_has_tl: bool) -> Ordering {
-    let a_segments = segment_iter(a);
-    let b_segments = segment_iter(b);
-    // cmp_by would be useful for us here but that is currently unstable
-    // cmp doesnt work due the lifetimes on text's return type
-    a_segments
-        .zip_longest(b_segments)
-        .find_map(|zipped| match zipped {
-            EitherOrBoth::Both(ref a, ref b) => match path_segment_cmp(a, b) {
-                Ordering::Equal => None,
-                ord => Some(ord),
-            },
-            EitherOrBoth::Left(_) if !b_has_tl => Some(Ordering::Greater),
-            EitherOrBoth::Left(_) => Some(Ordering::Less),
-            EitherOrBoth::Right(_) if !a_has_tl => Some(Ordering::Less),
-            EitherOrBoth::Right(_) => Some(Ordering::Greater),
-        })
-        .unwrap_or(Ordering::Equal)
-}
-
-fn path_segment_cmp(a: &ast::PathSegment, b: &ast::PathSegment) -> Ordering {
-    let a = a.kind().and_then(|kind| match kind {
-        PathSegmentKind::Name(name_ref) => Some(name_ref),
-        _ => None,
-    });
-    let b = b.kind().and_then(|kind| match kind {
-        PathSegmentKind::Name(name_ref) => Some(name_ref),
-        _ => None,
-    });
-    a.as_ref().map(ast::NameRef::text).cmp(&b.as_ref().map(ast::NameRef::text))
-}
-
-/// What type of merges are allowed.
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum MergeBehavior {
-    /// Merge everything together creating deeply nested imports.
-    Full,
-    /// Only merge the last import level, doesn't allow import nesting.
-    Last,
-}
-
-impl MergeBehavior {
-    #[inline]
-    fn is_tree_allowed(&self, tree: &ast::UseTree) -> bool {
-        match self {
-            MergeBehavior::Full => true,
-            // only simple single segment paths are allowed
-            MergeBehavior::Last => {
-                tree.use_tree_list().is_none() && tree.path().map(path_len) <= Some(1)
-            }
-        }
-    }
-}
-
 #[derive(Eq, PartialEq, PartialOrd, Ord)]
 enum ImportGroup {
     // the order here defines the order of new group inserts
@@ -411,7 +101,7 @@ impl ImportGroup {
     fn new(path: &ast::Path) -> ImportGroup {
         let default = ImportGroup::ExternCrate;
 
-        let first_segment = match first_segment(path) {
+        let first_segment = match path.first_segment() {
             Some(it) => it,
             None => return default,
         };
diff --git a/crates/ide_db/src/helpers/merge_imports.rs b/crates/ide_db/src/helpers/merge_imports.rs
new file mode 100644
index 000000000..3f5bbef7f
--- /dev/null
+++ b/crates/ide_db/src/helpers/merge_imports.rs
@@ -0,0 +1,309 @@
+//! Handle syntactic aspects of merging UseTrees.
+use std::cmp::Ordering;
+
+use itertools::{EitherOrBoth, Itertools};
+use syntax::ast::{
+    self, edit::AstNodeEdit, make, AstNode, AttrsOwner, PathSegmentKind, VisibilityOwner,
+};
+
+/// What type of merges are allowed.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum MergeBehavior {
+    /// Merge everything together creating deeply nested imports.
+    Full,
+    /// Only merge the last import level, doesn't allow import nesting.
+    Last,
+}
+
+impl MergeBehavior {
+    #[inline]
+    fn is_tree_allowed(&self, tree: &ast::UseTree) -> bool {
+        match self {
+            MergeBehavior::Full => true,
+            // only simple single segment paths are allowed
+            MergeBehavior::Last => {
+                tree.use_tree_list().is_none() && tree.path().map(path_len) <= Some(1)
+            }
+        }
+    }
+}
+
+pub fn try_merge_imports(
+    lhs: &ast::Use,
+    rhs: &ast::Use,
+    merge_behavior: MergeBehavior,
+) -> Option<ast::Use> {
+    // don't merge imports with different visibilities
+    if !eq_visibility(lhs.visibility(), rhs.visibility()) {
+        return None;
+    }
+    if !eq_attrs(lhs.attrs(), rhs.attrs()) {
+        return None;
+    }
+
+    let lhs_tree = lhs.use_tree()?;
+    let rhs_tree = rhs.use_tree()?;
+    let merged = try_merge_trees(&lhs_tree, &rhs_tree, merge_behavior)?;
+    Some(lhs.with_use_tree(merged).clone_for_update())
+}
+
+pub fn try_merge_trees(
+    lhs: &ast::UseTree,
+    rhs: &ast::UseTree,
+    merge: MergeBehavior,
+) -> Option<ast::UseTree> {
+    let lhs_path = lhs.path()?;
+    let rhs_path = rhs.path()?;
+
+    let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
+    let (lhs, rhs) = if lhs.is_simple_path()
+        && rhs.is_simple_path()
+        && 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)
+}
+
+/// Recursively "zips" together lhs and rhs.
+fn recursive_merge(
+    lhs: &ast::UseTree,
+    rhs: &ast::UseTree,
+    merge: MergeBehavior,
+) -> Option<ast::UseTree> {
+    let mut use_trees = lhs
+        .use_tree_list()
+        .into_iter()
+        .flat_map(|list| list.use_trees())
+        // we use Option here to early return from this function(this is not the same as a `filter` op)
+        .map(|tree| match merge.is_tree_allowed(&tree) {
+            true => Some(tree),
+            false => None,
+        })
+        .collect::<Option<Vec<_>>>()?;
+    use_trees.sort_unstable_by(|a, b| path_cmp_for_sort(a.path(), b.path()));
+    for rhs_t in rhs.use_tree_list().into_iter().flat_map(|list| list.use_trees()) {
+        if !merge.is_tree_allowed(&rhs_t) {
+            return None;
+        }
+        let rhs_path = rhs_t.path();
+        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()?;
+                let rhs_path = rhs_path?;
+                let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
+                if lhs_prefix == lhs_path && rhs_prefix == rhs_path {
+                    let tree_is_self = |tree: ast::UseTree| {
+                        tree.path().as_ref().map(path_is_self).unwrap_or(false)
+                    };
+                    // check if only one of the two trees has a tree list, and whether that then contains `self` or not.
+                    // If this is the case we can skip this iteration since the path without the list is already included in the other one via `self`
+                    let tree_contains_self = |tree: &ast::UseTree| {
+                        tree.use_tree_list()
+                            .map(|tree_list| tree_list.use_trees().any(tree_is_self))
+                            .unwrap_or(false)
+                    };
+                    match (tree_contains_self(&lhs_t), tree_contains_self(&rhs_t)) {
+                        (true, false) => continue,
+                        (false, true) => {
+                            *lhs_t = rhs_t;
+                            continue;
+                        }
+                        _ => (),
+                    }
+
+                    // glob imports arent part of the use-tree lists so we need to special handle them here as well
+                    // this special handling is only required for when we merge a module import into a glob import of said module
+                    // see the `merge_self_glob` or `merge_mod_into_glob` tests
+                    if lhs_t.star_token().is_some() || rhs_t.star_token().is_some() {
+                        *lhs_t = make::use_tree(
+                            make::path_unqualified(make::path_segment_self()),
+                            None,
+                            None,
+                            false,
+                        );
+                        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);
+                match recursive_merge(&lhs, &rhs, merge) {
+                    Some(use_tree) => use_trees[idx] = use_tree,
+                    None => return None,
+                }
+            }
+            Err(_)
+                if merge == MergeBehavior::Last
+                    && use_trees.len() > 0
+                    && rhs_t.use_tree_list().is_some() =>
+            {
+                return None
+            }
+            Err(idx) => {
+                use_trees.insert(idx, rhs_t);
+            }
+        }
+    }
+
+    Some(if let Some(old) = lhs.use_tree_list() {
+        lhs.replace_descendant(old, make::use_tree_list(use_trees)).clone_for_update()
+    } else {
+        lhs.clone()
+    })
+}
+
+/// Traverses both paths until they differ, returning the common prefix of both.
+fn common_prefix(lhs: &ast::Path, rhs: &ast::Path) -> Option<(ast::Path, ast::Path)> {
+    let mut res = None;
+    let mut lhs_curr = lhs.first_qualifier_or_self();
+    let mut rhs_curr = rhs.first_qualifier_or_self();
+    loop {
+        match (lhs_curr.segment(), rhs_curr.segment()) {
+            (Some(lhs), Some(rhs)) if lhs.syntax().text() == rhs.syntax().text() => (),
+            _ => break res,
+        }
+        res = Some((lhs_curr.clone(), rhs_curr.clone()));
+
+        match lhs_curr.parent_path().zip(rhs_curr.parent_path()) {
+            Some((lhs, rhs)) => {
+                lhs_curr = lhs;
+                rhs_curr = rhs;
+            }
+            _ => break res,
+        }
+    }
+}
+
+/// Orders paths in the following way:
+/// the sole self token comes first, after that come uppercase identifiers, then lowercase identifiers
+// FIXME: rustfmt sorts lowercase idents before uppercase, in general we want to have the same ordering rustfmt has
+// which is `self` and `super` first, then identifier imports with lowercase ones first, then glob imports and at last list imports.
+// Example foo::{self, foo, baz, Baz, Qux, *, {Bar}}
+fn path_cmp_for_sort(a: Option<ast::Path>, b: Option<ast::Path>) -> Ordering {
+    match (a, b) {
+        (None, None) => Ordering::Equal,
+        (None, Some(_)) => Ordering::Less,
+        (Some(_), None) => Ordering::Greater,
+        (Some(ref a), Some(ref b)) => match (path_is_self(a), path_is_self(b)) {
+            (true, true) => Ordering::Equal,
+            (true, false) => Ordering::Less,
+            (false, true) => Ordering::Greater,
+            (false, false) => path_cmp_short(a, b),
+        },
+    }
+}
+
+/// Path comparison func for binary searching for merging.
+fn path_cmp_bin_search(lhs: Option<ast::Path>, rhs: Option<ast::Path>) -> Ordering {
+    match (
+        lhs.as_ref().and_then(ast::Path::first_segment),
+        rhs.as_ref().and_then(ast::Path::first_segment),
+    ) {
+        (None, None) => Ordering::Equal,
+        (None, Some(_)) => Ordering::Less,
+        (Some(_), None) => Ordering::Greater,
+        (Some(ref a), Some(ref b)) => path_segment_cmp(a, b),
+    }
+}
+
+/// Short circuiting comparison, if both paths are equal until one of them ends they are considered
+/// equal
+fn path_cmp_short(a: &ast::Path, b: &ast::Path) -> Ordering {
+    let a = a.segments();
+    let b = b.segments();
+    // cmp_by would be useful for us here but that is currently unstable
+    // cmp doesn't work due the lifetimes on text's return type
+    a.zip(b)
+        .find_map(|(a, b)| match path_segment_cmp(&a, &b) {
+            Ordering::Equal => None,
+            ord => Some(ord),
+        })
+        .unwrap_or(Ordering::Equal)
+}
+
+/// Compares two paths, if one ends earlier than the other the has_tl parameters decide which is
+/// greater as a a path that has a tree list should be greater, while one that just ends without
+/// a tree list should be considered less.
+pub(super) fn use_tree_path_cmp(
+    a: &ast::Path,
+    a_has_tl: bool,
+    b: &ast::Path,
+    b_has_tl: bool,
+) -> Ordering {
+    let a_segments = a.segments();
+    let b_segments = b.segments();
+    // cmp_by would be useful for us here but that is currently unstable
+    // cmp doesn't work due the lifetimes on text's return type
+    a_segments
+        .zip_longest(b_segments)
+        .find_map(|zipped| match zipped {
+            EitherOrBoth::Both(ref a, ref b) => match path_segment_cmp(a, b) {
+                Ordering::Equal => None,
+                ord => Some(ord),
+            },
+            EitherOrBoth::Left(_) if !b_has_tl => Some(Ordering::Greater),
+            EitherOrBoth::Left(_) => Some(Ordering::Less),
+            EitherOrBoth::Right(_) if !a_has_tl => Some(Ordering::Less),
+            EitherOrBoth::Right(_) => Some(Ordering::Greater),
+        })
+        .unwrap_or(Ordering::Equal)
+}
+
+fn path_segment_cmp(a: &ast::PathSegment, b: &ast::PathSegment) -> Ordering {
+    let a = a.kind().and_then(|kind| match kind {
+        PathSegmentKind::Name(name_ref) => Some(name_ref),
+        _ => None,
+    });
+    let b = b.kind().and_then(|kind| match kind {
+        PathSegmentKind::Name(name_ref) => Some(name_ref),
+        _ => None,
+    });
+    a.as_ref().map(ast::NameRef::text).cmp(&b.as_ref().map(ast::NameRef::text))
+}
+
+fn eq_visibility(vis0: Option<ast::Visibility>, vis1: Option<ast::Visibility>) -> bool {
+    match (vis0, vis1) {
+        (None, None) => true,
+        // FIXME: Don't use the string representation to check for equality
+        // spaces inside of the node would break this comparison
+        (Some(vis0), Some(vis1)) => vis0.to_string() == vis1.to_string(),
+        _ => false,
+    }
+}
+
+fn eq_attrs(
+    attrs0: impl Iterator<Item = ast::Attr>,
+    attrs1: impl Iterator<Item = ast::Attr>,
+) -> bool {
+    let attrs0 = attrs0.map(|attr| attr.to_string());
+    let attrs1 = attrs1.map(|attr| attr.to_string());
+    attrs0.eq(attrs1)
+}
+
+fn path_is_self(path: &ast::Path) -> bool {
+    path.segment().and_then(|seg| seg.self_token()).is_some() && path.qualifier().is_none()
+}
+
+fn path_len(path: ast::Path) -> usize {
+    path.segments().count()
+}
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index 1109d2daf..d81ee94ee 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -12,7 +12,8 @@ use std::{ffi::OsString, iter, path::PathBuf};
 use flycheck::FlycheckConfig;
 use ide::{AssistConfig, CompletionConfig, DiagnosticsConfig, HoverConfig, InlayHintsConfig};
 use ide_db::helpers::{
-    insert_use::{InsertUseConfig, MergeBehavior, PrefixKind},
+    insert_use::{InsertUseConfig, PrefixKind},
+    merge_imports::MergeBehavior,
     SnippetCap,
 };
 use lsp_types::{ClientCapabilities, MarkupKind};
diff --git a/crates/syntax/src/ast/node_ext.rs b/crates/syntax/src/ast/node_ext.rs
index 171099661..492fbc4a0 100644
--- a/crates/syntax/src/ast/node_ext.rs
+++ b/crates/syntax/src/ast/node_ext.rs
@@ -1,7 +1,7 @@
 //! Various extension methods to ast Nodes, which are hard to code-generate.
 //! Extensions for various expressions live in a sibling `expr_extensions` module.
 
-use std::fmt;
+use std::{fmt, iter::successors};
 
 use itertools::Itertools;
 use parser::SyntaxKind;
@@ -237,6 +237,26 @@ impl ast::Path {
             None => self.segment(),
         }
     }
+
+    pub fn first_qualifier_or_self(&self) -> ast::Path {
+        successors(Some(self.clone()), ast::Path::qualifier).last().unwrap()
+    }
+
+    pub fn first_segment(&self) -> Option<ast::PathSegment> {
+        self.first_qualifier_or_self().segment()
+    }
+
+    pub fn segments(&self) -> impl Iterator<Item = ast::PathSegment> + Clone {
+        // cant make use of SyntaxNode::siblings, because the returned Iterator is not clone
+        successors(self.first_segment(), |p| {
+            p.parent_path().parent_path().and_then(|p| p.segment())
+        })
+    }
+}
+impl ast::UseTree {
+    pub fn is_simple_path(&self) -> bool {
+        self.use_tree_list().is_none() && self.star_token().is_none()
+    }
 }
 
 impl ast::UseTreeList {