1 files changed, 102 insertions, 8 deletions

diff --git a/crates/assists/src/handlers/replace_impl_trait_with_generic.rs b/crates/assists/src/handlers/replace_impl_trait_with_generic.rs
index 8af2d16dd..5b0d5d971 100644
--- a/crates/assists/src/handlers/replace_impl_trait_with_generic.rs
+++ b/crates/assists/src/handlers/replace_impl_trait_with_generic.rs
@@ -13,9 +13,6 @@ pub(crate) fn replace_impl_trait_with_generic(
     let type_param = type_impl_trait.syntax().parent().and_then(ast::Param::cast)?;
     let type_fn = type_param.syntax().ancestors().nth(2).and_then(ast::Fn::cast)?;
 
-    let generic_param_list =
-        type_fn.generic_param_list().unwrap_or_else(|| make::generic_param_list(None));
-
     let impl_trait_ty = type_impl_trait
         .syntax()
         .descendants()
@@ -31,11 +28,16 @@ pub(crate) fn replace_impl_trait_with_generic(
         target,
         |edit| {
             let generic_letter = impl_trait_ty[..1].to_string();
-            edit.replace_ast::<ast::Type>(type_impl_trait.into(), make::ty(&generic_letter));
 
-            let new_params = generic_param_list
-                .append_param(make::generic_param(generic_letter, Some(impl_trait_ty)));
-            let new_type_fn = type_fn.replace_descendant(generic_param_list, new_params);
+            let generic_param_list = type_fn
+                .generic_param_list()
+                .unwrap_or_else(|| make::generic_param_list(None))
+                .append_param(make::generic_param(generic_letter.clone(), Some(impl_trait_ty)));
+
+            let new_type_fn = type_fn
+                .replace_descendant::<ast::Type>(type_impl_trait.into(), make::ty(&generic_letter))
+                .with_generic_params(generic_param_list);
+
             edit.replace_ast(type_fn.clone(), new_type_fn);
         },
     )
@@ -48,7 +50,7 @@ mod tests {
     use crate::tests::check_assist;
 
     #[test]
-    fn replace_with_generic_params() {
+    fn replace_impl_trait_with_generic_params() {
         check_assist(
             replace_impl_trait_with_generic,
             r#"
@@ -59,4 +61,96 @@ mod tests {
             "#,
         );
     }
+
+    #[test]
+    fn replace_impl_trait_without_generic_params() {
+        check_assist(
+            replace_impl_trait_with_generic,
+            r#"
+            fn foo(bar: <|>impl Bar) {}
+            "#,
+            r#"
+            fn foo<B: Bar>(bar: B) {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn replace_two_impl_trait_with_generic_params() {
+        check_assist(
+            replace_impl_trait_with_generic,
+            r#"
+            fn foo<G>(foo: impl Foo, bar: <|>impl Bar) {}
+            "#,
+            r#"
+            fn foo<G, B: Bar>(foo: impl Foo, bar: B) {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn replace_impl_trait_with_empty_generic_params() {
+        check_assist(
+            replace_impl_trait_with_generic,
+            r#"
+            fn foo<>(bar: <|>impl Bar) {}
+            "#,
+            r#"
+            fn foo<B: Bar>(bar: B) {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn replace_impl_trait_with_empty_multiline_generic_params() {
+        // FIXME: It would be more correct to place the generic parameter
+        // on the next line after the left angle.
+        check_assist(
+            replace_impl_trait_with_generic,
+            r#"
+            fn foo<
+            >(bar: <|>impl Bar) {}
+            "#,
+            r#"
+            fn foo<B: Bar,
+            >(bar: B) {}
+            "#,
+        );
+    }
+
+    #[test]
+    #[ignore = "This case is very rare but there is no simple solutions to fix it."]
+    fn replace_impl_trait_with_exist_generic_letter() {
+        check_assist(
+            replace_impl_trait_with_generic,
+            r#"
+            fn foo<B>(bar: <|>impl Bar) {}
+            "#,
+            r#"
+            fn foo<B, C: Bar>(bar: C) {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn replace_impl_trait_with_multiline_generic_params() {
+        check_assist(
+            replace_impl_trait_with_generic,
+            r#"
+            fn foo<
+                G: Foo,
+                F,
+                H,
+            >(bar: <|>impl Bar) {}
+            "#,
+            r#"
+            fn foo<
+                G: Foo,
+                F,
+                H,
+                B: Bar,
+            >(bar: B) {}
+            "#,
+        );
+    }
 }