Deduplicate references when some of them are in macro expansions

Commit 6a06f6f (Deduplicate reference search results, 2022-11-07)
deduplicates references within each definition.

Apparently our descend_into_macros() stanza returns
one definition for each time a name is used in a macro.
Each of those definitions has the same set of references.
We return them all, leading to many redundant references.

Work around this by deduplicating definitions as well.  Perhaps there
is a better fix to not produce duplicate definitions in the first
place.

I discovered this working with the "bitflags" macro from the crate
of the same name.

Fixes #16357

Author: krobelus

crates/ide/src/references.rs

@@ -120,7 +120,13 @@ pub(crate) fn find_all_refs(
         }
         None => {
             let search = make_searcher(false);
-            Some(find_defs(sema, &syntax, position.offset)?.into_iter().map(search).collect())
+            Some(
+                find_defs(sema, &syntax, position.offset)?
+                    .into_iter()
+                    .unique()
+                    .map(search)
+                    .collect(),
+            )
         }
     }
 }
@@ -2139,4 +2145,28 @@ fn test() {
             "#]],
         );
     }
+
+    #[test]
+    fn multiple_references_inside_macro() {
+        check(
+            r#"
+macro_rules! use_name {
+    ($name:ident) => {
+        let _ = $name;
+        let _ = $name;
+        let _ = $name;
+    };
+}
+fn test() {
+    let name = ();
+    use_name!(name$0);
+}
+"#,
+            expect![[r#"
+                name Local FileId(0) 145..149 145..149
+
+                FileId(0) 170..174 Read
+            "#]],
+        );
+    }
 }