From 95910108dc12e262b4d49bd7b08796b9bfaff6e0 Mon Sep 17 00:00:00 2001
From: Sebastian Ullrich <sebasti@nullri.ch>
Date: Tue, 3 Nov 2020 11:13:20 +0100
Subject: [PATCH] fix: delaborator: share mdata tree position with child

---
 src/Lean/Delaborator.lean | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Lean/Delaborator.lean b/src/Lean/Delaborator.lean
index fe5222772d..b234d66f6b 100644
--- a/src/Lean/Delaborator.lean
+++ b/src/Lean/Delaborator.lean
@@ -214,7 +214,8 @@ def withProj {α} (d : DelabM α) : DelabM α := do
 
 def withMDataExpr {α} (d : DelabM α) : DelabM α := do
   let Expr.mdata _ e _ ← getExpr | unreachable!
-  descend e 0 d
+  -- do not change position so that options on an mdata are automatically forwarded to the child
+  withReader ({ · with expr := e }) d
 
 partial def annotatePos (pos : Nat) : Syntax → Syntax
   | stx@(Syntax.ident _ _ _ _)                   => stx.setInfo { pos := pos }