Merge #3745

3745: Fix merge-imports assist for wildcard imports r=matklad a=piotr-szpetkowski

Refs #3728 

Besides the case mentioned in issue merging two diff-prefix wildcard uses will now work as well e.g. 

```rust
use std::cell::*;
use std::str::*;
```

will translate into:

```rust
use std::{cell::*, str::*}
```

I'd also like to explore usage of the `merge-imports` for same-prefix uses to simplify redundancy, but it seems like an idea for another issue and I'm not sure if it's something that this assist should do e.g.:

```rust
use std::cell::Cell;
use std::cell::*;
```

into:

```rust
use std::cell::*;
```

Co-authored-by: Piotr Szpetkowski <[email protected]>

1 files changed, 28 insertions, 0 deletions

diff --git a/crates/ra_assists/src/handlers/merge_imports.rs b/crates/ra_assists/src/handlers/merge_imports.rs
index 9c57d1e30..5d4b74e56 100644
--- a/crates/ra_assists/src/handlers/merge_imports.rs
+++ b/crates/ra_assists/src/handlers/merge_imports.rs
@@ -171,6 +171,34 @@ use std::{fmt::<|>{Display, Debug}};
     }
 
     #[test]
+    fn test_merge_single_wildcard_diff_prefixes() {
+        check_assist(
+            merge_imports,
+            r"
+use std<|>::cell::*;
+use std::str;
+",
+            r"
+use std<|>::{cell::*, str};
+",
+        )
+    }
+
+    #[test]
+    fn test_merge_both_wildcard_diff_prefixes() {
+        check_assist(
+            merge_imports,
+            r"
+use std<|>::cell::*;
+use std::str::*;
+",
+            r"
+use std<|>::{cell::*, str::*};
+",
+        )
+    }
+
+    #[test]
     fn removes_just_enough_whitespace() {
         check_assist(
             merge_imports,