Fix panic in split_imports assist

The fix is admittedly quit literally just papering over.

Long-term, I see two more principled approaches:

* we switch to a fully tree-based impl, without parse . to_string
  step; with this approach, there shouldn't be any panics. The results
  might be nonsensical, but so was the original input.

* we preserve the invariant that re-parsing constructed node is an
  identity, and make all the `make_xxx` method return an `Option`.

closes #4044

1 files changed, 6 insertions, 1 deletions

diff --git a/crates/ra_assists/src/handlers/split_import.rs b/crates/ra_assists/src/handlers/split_import.rs
index d9244f22d..f25826796 100644
--- a/crates/ra_assists/src/handlers/split_import.rs
+++ b/crates/ra_assists/src/handlers/split_import.rs
@@ -37,7 +37,7 @@ pub(crate) fn split_import(ctx: AssistCtx) -> Option<Assist> {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_target};
+    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::*;
 
@@ -63,4 +63,9 @@ mod tests {
     fn split_import_target() {
         check_assist_target(split_import, "use crate::<|>db::{RootDatabase, FileSymbol}", "::");
     }
+
+    #[test]
+    fn issue4044() {
+        check_assist_not_applicable(split_import, "use crate::<|>:::self;")
+    }
 }