fixes #10689

compiler/injectdestructors.nim

@@ -796,7 +796,11 @@ proc p(n: PNode; c: var Con): PNode =
       result = n
   of nkAsgn, nkFastAsgn:
     if hasDestructor(n[0].typ) and n[1].kind notin {nkProcDef, nkDo, nkLambda}:
-      result = moveOrCopy(n[0], n[1], c)
+      # rule (self-assignment-removal):
+      if n[1].kind == nkSym and n[0].kind == nkSym and n[0].sym == n[1].sym:
+        result = newNodeI(nkEmpty, n.info)
+      else:
+        result = moveOrCopy(n[0], n[1], c)
     else:
       result = copyNode(n)
       recurse(n, result)

tests/destructor/tnewruntime_misc.nim

@@ -3,6 +3,7 @@ discard """
   output: '''(field: "value")
 Indeed
 axc
+(v: 10)
 0  new: 0'''
 """
 
@@ -58,5 +59,21 @@ proc test(p: owned proc()) =
 
 test(proc() = discard)
 
+# bug #10689
+
+type
+  O = object
+    v: int
+
+proc `=sink`(d: var O, s: O) =
+  d.v = s.v
+
+proc selfAssign =
+  var o = O(v: 10)
+  o = o
+  echo o
+
+selfAssign()
+
 let (a, d) = allocCounters()
 discard cprintf("%ld  new: %ld\n", a - unpairedEnvAllocs() - d, allocs)