fix: set of chained lexical references

src/Lean/Server/References.lean

@@ -147,13 +147,11 @@ partial def combineFvars (refs : Array Reference) : Array Reference := Id.run do
   let mut refs' := #[]
   for ref in refs do
     match ref with
-    | { ident := RefIdent.fvar id, range, isBinder := true } =>
-      -- Since deduplication works via definitions, we know that a definition
-      -- for the base id exists.
-      unless idMap.contains id do  -- Only keep the base definition
-        refs' := refs'.push ref
-    | { ident, range, isBinder := false } =>
-      refs' := refs'.push { ident := applyIdMap idMap ident, range, isBinder := false }
+    | { ident := ident@(RefIdent.fvar id), range, isBinder } =>
+      -- downgrade chained definitions to usages
+      -- (we shouldn't completely remove them in case they do not have usages)
+      let isBinder := isBinder && !idMap.contains id
+      refs' := refs'.push { ident := applyIdMap idMap ident, range, isBinder }
     | _ =>
       refs' := refs'.push ref
   refs'

tests/lean/interactive/highlight.lean

@@ -41,3 +41,10 @@ example : Nat := Id.run do
     return y
   pure y
      --^ textDocument/documentHighlight
+
+example : Nat := Id.run do
+  let mut y := 0
+  if true then
+    y := 1
+  return y  -- TODO: definition should be first `y`
+       --^ textDocument/documentHighlight

tests/lean/interactive/highlight.lean.expected.out

@@ -104,3 +104,15 @@
  {"range":
   {"start": {"line": 41, "character": 7}, "end": {"line": 41, "character": 8}},
   "kind": 1}]
+{"textDocument": {"uri": "file://highlight.lean"},
+ "position": {"line": 48, "character": 9}}
+[{"range":
+  {"start": {"line": 47, "character": 4}, "end": {"line": 47, "character": 5}},
+  "kind": 1},
+ {"range":
+  {"start": {"line": 45, "character": 10},
+   "end": {"line": 45, "character": 11}},
+  "kind": 1},
+ {"range":
+  {"start": {"line": 48, "character": 9}, "end": {"line": 48, "character": 10}},
+  "kind": 1}]