Merge #6172

6172: Add qualify path assist r=matklad a=Veykril

This implements a `qualify_path` assist which works quite similar to the `auto_import` assist but instead of adding imports to the file it well, qualifies the path. This PR also moves out the `AutoImportAssets` struct and functions from `auto_import` into a utils submodule as most of this is now shared between `auto_import` and `qualify_path`.

Changes made to `AutoImportAssets` are solely in its `search_for_imports` function which now takes a prefixed parameter to discern between using `find_use_path_prefixed` and `find_use_path` as the former is the required behavior by `auto_import` and the latter by this assist.

For missing imported traits instead of importing this will qualify the path with a trait cast as in:
```rust
test_mod::TestStruct::TEST_CONST<|>
```
becomes
```rust
<test_mod::TestStruct as test_mod::TestTrait>::TEST_CONST
```

and for trait methods ideally it would do the following:
```rust
let test_struct = test_mod::TestStruct {};
test_struct.test_meth<|>od()
```
becomes
```rust
let test_struct = test_mod::TestStruct {};
test_mod::TestTrait::test_method(&test_struct)
```

Fixes #4124.

Co-authored-by: Lukas Wirth <[email protected]>

5 files changed, 1087 insertions, 24 deletions

diff --git a/crates/assists/src/handlers/auto_import.rs b/crates/assists/src/handlers/auto_import.rs
index ccf575e84..e49e641b3 100644
--- a/crates/assists/src/handlers/auto_import.rs
+++ b/crates/assists/src/handlers/auto_import.rs
@@ -100,7 +100,7 @@ pub(crate) fn auto_import(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
     let group = import_group_message(import_assets.import_candidate());
     let scope = ImportScope::find_insert_use_container(import_assets.syntax_under_caret(), ctx)?;
     let syntax = scope.as_syntax_node();
-    for import in proposed_imports {
+    for (import, _) in proposed_imports {
         acc.add_group(
             &group,
             AssistId("auto_import", AssistKind::QuickFix),
diff --git a/crates/assists/src/handlers/qualify_path.rs b/crates/assists/src/handlers/qualify_path.rs
new file mode 100644
index 000000000..f436bdbbf
--- /dev/null
+++ b/crates/assists/src/handlers/qualify_path.rs
@@ -0,0 +1,1048 @@
+use std::iter;
+
+use hir::AsName;
+use ide_db::RootDatabase;
+use syntax::{
+    ast,
+    ast::{make, ArgListOwner},
+    AstNode,
+};
+use test_utils::mark;
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::import_assets::{ImportAssets, ImportCandidate},
+    utils::mod_path_to_ast,
+    AssistId, AssistKind, GroupLabel,
+};
+
+// Assist: qualify_path
+//
+// If the name is unresolved, provides all possible qualified paths for it.
+//
+// ```
+// fn main() {
+//     let map = HashMap<|>::new();
+// }
+// # pub mod std { pub mod collections { pub struct HashMap { } } }
+// ```
+// ->
+// ```
+// fn main() {
+//     let map = std::collections::HashMap::new();
+// }
+// # pub mod std { pub mod collections { pub struct HashMap { } } }
+// ```
+pub(crate) fn qualify_path(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let import_assets =
+        if let Some(path_under_caret) = ctx.find_node_at_offset_with_descend::<ast::Path>() {
+            ImportAssets::for_regular_path(path_under_caret, &ctx.sema)
+        } else if let Some(method_under_caret) =
+            ctx.find_node_at_offset_with_descend::<ast::MethodCallExpr>()
+        {
+            ImportAssets::for_method_call(method_under_caret, &ctx.sema)
+        } else {
+            None
+        }?;
+    let proposed_imports = import_assets.search_for_relative_paths(&ctx.sema);
+    if proposed_imports.is_empty() {
+        return None;
+    }
+
+    let candidate = import_assets.import_candidate();
+    let range = ctx.sema.original_range(import_assets.syntax_under_caret()).range;
+
+    let qualify_candidate = match candidate {
+        ImportCandidate::QualifierStart(_) => {
+            mark::hit!(qualify_path_qualifier_start);
+            let path = ast::Path::cast(import_assets.syntax_under_caret().clone())?;
+            let segment = path.segment()?;
+            QualifyCandidate::QualifierStart(segment)
+        }
+        ImportCandidate::UnqualifiedName(_) => {
+            mark::hit!(qualify_path_unqualified_name);
+            QualifyCandidate::UnqualifiedName
+        }
+        ImportCandidate::TraitAssocItem(_) => {
+            mark::hit!(qualify_path_trait_assoc_item);
+            let path = ast::Path::cast(import_assets.syntax_under_caret().clone())?;
+            let (qualifier, segment) = (path.qualifier()?, path.segment()?);
+            QualifyCandidate::TraitAssocItem(qualifier, segment)
+        }
+        ImportCandidate::TraitMethod(_) => {
+            mark::hit!(qualify_path_trait_method);
+            let mcall_expr = ast::MethodCallExpr::cast(import_assets.syntax_under_caret().clone())?;
+            QualifyCandidate::TraitMethod(ctx.sema.db, mcall_expr)
+        }
+    };
+
+    let group_label = group_label(candidate);
+    for (import, item) in proposed_imports {
+        acc.add_group(
+            &group_label,
+            AssistId("qualify_path", AssistKind::QuickFix),
+            label(candidate, &import),
+            range,
+            |builder| {
+                qualify_candidate.qualify(
+                    |replace_with: String| builder.replace(range, replace_with),
+                    import,
+                    item,
+                )
+            },
+        );
+    }
+    Some(())
+}
+
+enum QualifyCandidate<'db> {
+    QualifierStart(ast::PathSegment),
+    UnqualifiedName,
+    TraitAssocItem(ast::Path, ast::PathSegment),
+    TraitMethod(&'db RootDatabase, ast::MethodCallExpr),
+}
+
+impl QualifyCandidate<'_> {
+    fn qualify(&self, mut replacer: impl FnMut(String), import: hir::ModPath, item: hir::ItemInNs) {
+        match self {
+            QualifyCandidate::QualifierStart(segment) => {
+                let import = mod_path_to_ast(&import);
+                replacer(format!("{}::{}", import, segment));
+            }
+            QualifyCandidate::UnqualifiedName => replacer(mod_path_to_ast(&import).to_string()),
+            QualifyCandidate::TraitAssocItem(qualifier, segment) => {
+                let import = mod_path_to_ast(&import);
+                replacer(format!("<{} as {}>::{}", qualifier, import, segment));
+            }
+            &QualifyCandidate::TraitMethod(db, ref mcall_expr) => {
+                Self::qualify_trait_method(db, mcall_expr, replacer, import, item);
+            }
+        }
+    }
+
+    fn qualify_trait_method(
+        db: &RootDatabase,
+        mcall_expr: &ast::MethodCallExpr,
+        mut replacer: impl FnMut(String),
+        import: hir::ModPath,
+        item: hir::ItemInNs,
+    ) -> Option<()> {
+        let receiver = mcall_expr.receiver()?;
+        let trait_method_name = mcall_expr.name_ref()?;
+        let arg_list = mcall_expr.arg_list().map(|arg_list| arg_list.args());
+        let trait_ = item_as_trait(item)?;
+        let method = find_trait_method(db, trait_, &trait_method_name)?;
+        if let Some(self_access) = method.self_param(db).map(|sp| sp.access(db)) {
+            let import = mod_path_to_ast(&import);
+            let receiver = match self_access {
+                hir::Access::Shared => make::expr_ref(receiver, false),
+                hir::Access::Exclusive => make::expr_ref(receiver, true),
+                hir::Access::Owned => receiver,
+            };
+            replacer(format!(
+                "{}::{}{}",
+                import,
+                trait_method_name,
+                match arg_list.clone() {
+                    Some(args) => make::arg_list(iter::once(receiver).chain(args)),
+                    None => make::arg_list(iter::once(receiver)),
+                }
+            ));
+        }
+        Some(())
+    }
+}
+
+fn find_trait_method(
+    db: &RootDatabase,
+    trait_: hir::Trait,
+    trait_method_name: &ast::NameRef,
+) -> Option<hir::Function> {
+    if let Some(hir::AssocItem::Function(method)) =
+        trait_.items(db).into_iter().find(|item: &hir::AssocItem| {
+            item.name(db).map(|name| name == trait_method_name.as_name()).unwrap_or(false)
+        })
+    {
+        Some(method)
+    } else {
+        None
+    }
+}
+
+fn item_as_trait(item: hir::ItemInNs) -> Option<hir::Trait> {
+    if let hir::ModuleDef::Trait(trait_) = hir::ModuleDef::from(item.as_module_def_id()?) {
+        Some(trait_)
+    } else {
+        None
+    }
+}
+
+fn group_label(candidate: &ImportCandidate) -> GroupLabel {
+    let name = match candidate {
+        ImportCandidate::UnqualifiedName(it) | ImportCandidate::QualifierStart(it) => &it.name,
+        ImportCandidate::TraitAssocItem(it) | ImportCandidate::TraitMethod(it) => &it.name,
+    };
+    GroupLabel(format!("Qualify {}", name))
+}
+
+fn label(candidate: &ImportCandidate, import: &hir::ModPath) -> String {
+    match candidate {
+        ImportCandidate::UnqualifiedName(_) => format!("Qualify as `{}`", &import),
+        ImportCandidate::QualifierStart(_) => format!("Qualify with `{}`", &import),
+        ImportCandidate::TraitAssocItem(_) => format!("Qualify `{}`", &import),
+        ImportCandidate::TraitMethod(_) => format!("Qualify with cast as `{}`", &import),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn applicable_when_found_an_import_partial() {
+        mark::check!(qualify_path_unqualified_name);
+        check_assist(
+            qualify_path,
+            r"
+            mod std {
+                pub mod fmt {
+                    pub struct Formatter;
+                }
+            }
+
+            use std::fmt;
+
+            <|>Formatter
+            ",
+            r"
+            mod std {
+                pub mod fmt {
+                    pub struct Formatter;
+                }
+            }
+
+            use std::fmt;
+
+            fmt::Formatter
+            ",
+        );
+    }
+
+    #[test]
+    fn applicable_when_found_an_import() {
+        check_assist(
+            qualify_path,
+            r"
+            <|>PubStruct
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            PubMod::PubStruct
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn applicable_in_macros() {
+        check_assist(
+            qualify_path,
+            r"
+            macro_rules! foo {
+                ($i:ident) => { fn foo(a: $i) {} }
+            }
+            foo!(Pub<|>Struct);
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            macro_rules! foo {
+                ($i:ident) => { fn foo(a: $i) {} }
+            }
+            foo!(PubMod::PubStruct);
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn applicable_when_found_multiple_imports() {
+        check_assist(
+            qualify_path,
+            r"
+            PubSt<|>ruct
+
+            pub mod PubMod1 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod2 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod3 {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            PubMod3::PubStruct
+
+            pub mod PubMod1 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod2 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod3 {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_already_imported_types() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            use PubMod::PubStruct;
+
+            PubStruct<|>
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_types_with_private_paths() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            PrivateStruct<|>
+
+            pub mod PubMod {
+                struct PrivateStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_when_no_imports_found() {
+        check_assist_not_applicable(
+            qualify_path,
+            "
+            PubStruct<|>",
+        );
+    }
+
+    #[test]
+    fn not_applicable_in_import_statements() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            use PubStruct<|>;
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }",
+        );
+    }
+
+    #[test]
+    fn qualify_function() {
+        check_assist(
+            qualify_path,
+            r"
+            test_function<|>
+
+            pub mod PubMod {
+                pub fn test_function() {};
+            }
+            ",
+            r"
+            PubMod::test_function
+
+            pub mod PubMod {
+                pub fn test_function() {};
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn qualify_macro() {
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:crate_with_macro
+#[macro_export]
+macro_rules! foo {
+    () => ()
+}
+
+//- /main.rs crate:main deps:crate_with_macro
+fn main() {
+    foo<|>
+}
+",
+            r"
+fn main() {
+    crate_with_macro::foo
+}
+",
+        );
+    }
+
+    #[test]
+    fn qualify_path_target() {
+        check_assist_target(
+            qualify_path,
+            r"
+            struct AssistInfo {
+                group_label: Option<<|>GroupLabel>,
+            }
+
+            mod m { pub struct GroupLabel; }
+            ",
+            "GroupLabel",
+        )
+    }
+
+    #[test]
+    fn not_applicable_when_path_start_is_imported() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            pub mod mod1 {
+                pub mod mod2 {
+                    pub mod mod3 {
+                        pub struct TestStruct;
+                    }
+                }
+            }
+
+            use mod1::mod2;
+            fn main() {
+                mod2::mod3::TestStruct<|>
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_function() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            pub mod test_mod {
+                pub fn test_function() {}
+            }
+
+            use test_mod::test_function;
+            fn main() {
+                test_function<|>
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn associated_struct_function() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    pub fn test_function() {}
+                }
+            }
+
+            fn main() {
+                TestStruct::test_function<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    pub fn test_function() {}
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::test_function
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn associated_struct_const() {
+        mark::check!(qualify_path_qualifier_start);
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                TestStruct::TEST_CONST<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::TEST_CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn associated_trait_function() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::test_function<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+
+            fn main() {
+                <test_mod::TestStruct as test_mod::TestTrait>::test_function
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_trait_for_function() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub trait TestTrait2 {
+                    fn test_function();
+                }
+                pub enum TestEnum {
+                    One,
+                    Two,
+                }
+                impl TestTrait2 for TestEnum {
+                    fn test_function() {}
+                }
+                impl TestTrait for TestEnum {
+                    fn test_function() {}
+                }
+            }
+
+            use test_mod::TestTrait2;
+            fn main() {
+                test_mod::TestEnum::test_function<|>;
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn associated_trait_const() {
+        mark::check!(qualify_path_trait_assoc_item);
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::TEST_CONST<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                <test_mod::TestStruct as test_mod::TestTrait>::TEST_CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_trait_for_const() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub trait TestTrait2 {
+                    const TEST_CONST: f64;
+                }
+                pub enum TestEnum {
+                    One,
+                    Two,
+                }
+                impl TestTrait2 for TestEnum {
+                    const TEST_CONST: f64 = 42.0;
+                }
+                impl TestTrait for TestEnum {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            use test_mod::TestTrait2;
+            fn main() {
+                test_mod::TestEnum::TEST_CONST<|>;
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn trait_method() {
+        mark::check!(qualify_path_trait_method);
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_mod::TestTrait::test_method(&test_struct)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn trait_method_multi_params() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self, test: i32);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self, test: i32) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_struct.test_meth<|>od(42)
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self, test: i32);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self, test: i32) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_mod::TestTrait::test_method(&test_struct, 42)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn trait_method_consume() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_mod::TestTrait::test_method(test_struct)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn trait_method_cross_crate() {
+        check_assist(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+            ",
+            r"
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                dep::test_mod::TestTrait::test_method(&test_struct)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn assoc_fn_cross_crate() {
+        check_assist(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                dep::test_mod::TestStruct::test_func<|>tion
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+            ",
+            r"
+            fn main() {
+                <dep::test_mod::TestStruct as dep::test_mod::TestTrait>::test_function
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn assoc_const_cross_crate() {
+        check_assist(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                dep::test_mod::TestStruct::CONST<|>
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    const CONST: bool;
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    const CONST: bool = true;
+                }
+            }
+            ",
+            r"
+            fn main() {
+                <dep::test_mod::TestStruct as dep::test_mod::TestTrait>::CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn assoc_fn_as_method_cross_crate() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                test_struct.test_func<|>tion()
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn private_trait_cross_crate() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_trait_for_method() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub trait TestTrait2 {
+                    fn test_method(&self);
+                }
+                pub enum TestEnum {
+                    One,
+                    Two,
+                }
+                impl TestTrait2 for TestEnum {
+                    fn test_method(&self) {}
+                }
+                impl TestTrait for TestEnum {
+                    fn test_method(&self) {}
+                }
+            }
+
+            use test_mod::TestTrait2;
+            fn main() {
+                let one = test_mod::TestEnum::One;
+                one.test<|>_method();
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn dep_import() {
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub struct Struct;
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    Struct<|>
+}
+",
+            r"
+fn main() {
+    dep::Struct
+}
+",
+        );
+    }
+
+    #[test]
+    fn whole_segment() {
+        // Tests that only imports whose last segment matches the identifier get suggested.
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub mod fmt {
+    pub trait Display {}
+}
+
+pub fn panic_fmt() {}
+
+//- /main.rs crate:main deps:dep
+struct S;
+
+impl f<|>mt::Display for S {}
+",
+            r"
+struct S;
+
+impl dep::fmt::Display for S {}
+",
+        );
+    }
+
+    #[test]
+    fn macro_generated() {
+        // Tests that macro-generated items are suggested from external crates.
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+macro_rules! mac {
+    () => {
+        pub struct Cheese;
+    };
+}
+
+mac!();
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    Cheese<|>;
+}
+",
+            r"
+fn main() {
+    dep::Cheese;
+}
+",
+        );
+    }
+
+    #[test]
+    fn casing() {
+        // Tests that differently cased names don't interfere and we only suggest the matching one.
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub struct FMT;
+pub struct fmt;
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    FMT<|>;
+}
+",
+            r"
+fn main() {
+    dep::FMT;
+}
+",
+        );
+    }
+}
diff --git a/crates/assists/src/lib.rs b/crates/assists/src/lib.rs
index a2bec818c..f29b8212f 100644
--- a/crates/assists/src/lib.rs
+++ b/crates/assists/src/lib.rs
@@ -150,6 +150,7 @@ mod handlers {
     mod merge_match_arms;
     mod move_bounds;
     mod move_guard;
+    mod qualify_path;
     mod raw_string;
     mod remove_dbg;
     mod remove_mut;
@@ -196,6 +197,7 @@ mod handlers {
             move_bounds::move_bounds_to_where_clause,
             move_guard::move_arm_cond_to_match_guard,
             move_guard::move_guard_to_arm_body,
+            qualify_path::qualify_path,
             raw_string::add_hash,
             raw_string::make_raw_string,
             raw_string::make_usual_string,
diff --git a/crates/assists/src/tests/generated.rs b/crates/assists/src/tests/generated.rs
index 41f536574..7d5618263 100644
--- a/crates/assists/src/tests/generated.rs
+++ b/crates/assists/src/tests/generated.rs
@@ -713,6 +713,25 @@ fn handle(action: Action) {
 }
 
 #[test]
+fn doctest_qualify_path() {
+    check_doc_test(
+        "qualify_path",
+        r#####"
+fn main() {
+    let map = HashMap<|>::new();
+}
+pub mod std { pub mod collections { pub struct HashMap { } } }
+"#####,
+        r#####"
+fn main() {
+    let map = std::collections::HashMap::new();
+}
+pub mod std { pub mod collections { pub struct HashMap { } } }
+"#####,
+    )
+}
+
+#[test]
 fn doctest_remove_dbg() {
     check_doc_test(
         "remove_dbg",
diff --git a/crates/assists/src/utils/import_assets.rs b/crates/assists/src/utils/import_assets.rs
index 601f51098..23db3a74b 100644
--- a/crates/assists/src/utils/import_assets.rs
+++ b/crates/assists/src/utils/import_assets.rs
@@ -1,6 +1,4 @@
 //! Look up accessible paths for items.
-use std::collections::BTreeSet;
-
 use either::Either;
 use hir::{AsAssocItem, AssocItemContainer, ModuleDef, Semantics};
 use ide_db::{imports_locator, RootDatabase};
@@ -29,12 +27,12 @@ pub(crate) enum ImportCandidate {
 #[derive(Debug)]
 pub(crate) struct TraitImportCandidate {
     pub ty: hir::Type,
-    pub name: String,
+    pub name: ast::NameRef,
 }
 
 #[derive(Debug)]
 pub(crate) struct PathImportCandidate {
-    pub name: String,
+    pub name: ast::NameRef,
 }
 
 #[derive(Debug)]
@@ -86,9 +84,9 @@ impl ImportAssets {
     fn get_search_query(&self) -> &str {
         match &self.import_candidate {
             ImportCandidate::UnqualifiedName(candidate)
-            | ImportCandidate::QualifierStart(candidate) => &candidate.name,
+            | ImportCandidate::QualifierStart(candidate) => candidate.name.text(),
             ImportCandidate::TraitAssocItem(candidate)
-            | ImportCandidate::TraitMethod(candidate) => &candidate.name,
+            | ImportCandidate::TraitMethod(candidate) => candidate.name.text(),
         }
     }
 
@@ -96,7 +94,7 @@ impl ImportAssets {
         &self,
         sema: &Semantics<RootDatabase>,
         config: &InsertUseConfig,
-    ) -> BTreeSet<hir::ModPath> {
+    ) -> Vec<(hir::ModPath, hir::ItemInNs)> {
         let _p = profile::span("import_assists::search_for_imports");
         self.search_for(sema, Some(config.prefix_kind))
     }
@@ -106,7 +104,7 @@ impl ImportAssets {
     pub(crate) fn search_for_relative_paths(
         &self,
         sema: &Semantics<RootDatabase>,
-    ) -> BTreeSet<hir::ModPath> {
+    ) -> Vec<(hir::ModPath, hir::ItemInNs)> {
         let _p = profile::span("import_assists::search_for_relative_paths");
         self.search_for(sema, None)
     }
@@ -115,7 +113,7 @@ impl ImportAssets {
         &self,
         sema: &Semantics<RootDatabase>,
         prefixed: Option<hir::PrefixKind>,
-    ) -> BTreeSet<hir::ModPath> {
+    ) -> Vec<(hir::ModPath, hir::ItemInNs)> {
         let db = sema.db;
         let mut trait_candidates = FxHashSet::default();
         let current_crate = self.module_with_name_to_import.krate();
@@ -181,7 +179,7 @@ impl ImportAssets {
             }
         };
 
-        imports_locator::find_imports(sema, current_crate, &self.get_search_query())
+        let mut res = imports_locator::find_imports(sema, current_crate, &self.get_search_query())
             .into_iter()
             .filter_map(filter)
             .filter_map(|candidate| {
@@ -191,10 +189,13 @@ impl ImportAssets {
                 } else {
                     self.module_with_name_to_import.find_use_path(db, item)
                 }
+                .map(|path| (path, item))
             })
-            .filter(|use_path| !use_path.segments.is_empty())
+            .filter(|(use_path, _)| !use_path.segments.is_empty())
             .take(20)
-            .collect::<BTreeSet<_>>()
+            .collect::<Vec<_>>();
+        res.sort_by_key(|(path, _)| path.clone());
+        res
     }
 
     fn assoc_to_trait(assoc: AssocItemContainer) -> Option<hir::Trait> {
@@ -215,7 +216,7 @@ impl ImportCandidate {
             Some(_) => None,
             None => Some(Self::TraitMethod(TraitImportCandidate {
                 ty: sema.type_of_expr(&method_call.receiver()?)?,
-                name: method_call.name_ref()?.syntax().to_string(),
+                name: method_call.name_ref()?,
             })),
         }
     }
@@ -243,24 +244,17 @@ impl ImportCandidate {
                     hir::PathResolution::Def(hir::ModuleDef::Adt(assoc_item_path)) => {
                         ImportCandidate::TraitAssocItem(TraitImportCandidate {
                             ty: assoc_item_path.ty(sema.db),
-                            name: segment.syntax().to_string(),
+                            name: segment.name_ref()?,
                         })
                     }
                     _ => return None,
                 }
             } else {
-                ImportCandidate::QualifierStart(PathImportCandidate {
-                    name: qualifier_start.syntax().to_string(),
-                })
+                ImportCandidate::QualifierStart(PathImportCandidate { name: qualifier_start })
             }
         } else {
             ImportCandidate::UnqualifiedName(PathImportCandidate {
-                name: segment
-                    .syntax()
-                    .descendants()
-                    .find_map(ast::NameRef::cast)?
-                    .syntax()
-                    .to_string(),
+                name: segment.syntax().descendants().find_map(ast::NameRef::cast)?,
             })
         };
         Some(candidate)