Don't unnecessarily unnest imports for import insertion

Author: Veykril

crates/assists/src/handlers/add_missing_impl_members.rs

@@ -414,6 +414,41 @@ impl foo::Foo for S {
         );
     }
 
+    #[test]
+    fn test_qualify_path_2() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub mod bar {
+        pub struct Bar;
+        pub trait Foo { fn foo(&self, bar: Bar); }
+    }
+}
+
+use foo::bar;
+
+struct S;
+impl bar::Foo for S { <|> }"#,
+            r#"
+mod foo {
+    pub mod bar {
+        pub struct Bar;
+        pub trait Foo { fn foo(&self, bar: Bar); }
+    }
+}
+
+use foo::bar;
+
+struct S;
+impl bar::Foo for S {
+    fn foo(&self, bar: bar::Bar) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
     #[test]
     fn test_qualify_path_generic() {
         check_assist(

crates/assists/src/handlers/auto_import.rs

@@ -196,10 +196,10 @@ impl AutoImportAssets {
             })
             .filter_map(|candidate| match candidate {
                 Either::Left(module_def) => {
-                    self.module_with_name_to_import.find_use_path(db, module_def)
+                    self.module_with_name_to_import.find_use_path_prefixed(db, module_def)
                 }
                 Either::Right(macro_def) => {
-                    self.module_with_name_to_import.find_use_path(db, macro_def)
+                    self.module_with_name_to_import.find_use_path_prefixed(db, macro_def)
                 }
             })
             .filter(|use_path| !use_path.segments.is_empty())
@@ -290,6 +290,35 @@ mod tests {
     use super::*;
     use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
+    #[test]
+    fn applicable_when_found_an_import_partial() {
+        check_assist(
+            auto_import,
+            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::{self, Formatter};
+
+            Formatter
+            ",
+        );
+    }
+
     #[test]
     fn applicable_when_found_an_import() {
         check_assist(

crates/hir/src/code_model.rs

@@ -383,6 +383,16 @@ impl Module {
     pub fn find_use_path(self, db: &dyn DefDatabase, item: impl Into<ItemInNs>) -> Option<ModPath> {
         hir_def::find_path::find_path(db, item.into(), self.into())
     }
+
+    /// Finds a path that can be used to refer to the given item from within
+    /// this module, if possible. This is used for returning import paths for use-statements.
+    pub fn find_use_path_prefixed(
+        self,
+        db: &dyn DefDatabase,
+        item: impl Into<ItemInNs>,
+    ) -> Option<ModPath> {
+        hir_def::find_path::find_path_prefixed(db, item.into(), self.into())
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]