fixes #18030 (#18415)

compiler/seminst.nim

@@ -146,8 +146,8 @@ proc instantiateBody(c: PContext, n, params: PNode, result, orig: PSym) =
     freshGenSyms(c, b, result, orig, symMap)
     b = semProcBody(c, b)
     result.ast[bodyPos] = hloBody(c, b)
-    trackProc(c, result, result.ast[bodyPos])
     excl(result.flags, sfForward)
+    trackProc(c, result, result.ast[bodyPos])
     dec c.inGenericInst
 
 proc fixupInstantiatedSymbols(c: PContext, s: PSym) =

tests/arc/tarcmisc.nim

@@ -28,6 +28,8 @@ aaaaa
 hello
 ok
 true
+copying
+123
 closed
 destroying variable: 20
 destroying variable: 10
@@ -433,3 +435,31 @@ proc t17712 =
   echo el != nil
 
 t17712()
+
+# bug #18030
+
+type
+  Foo = object
+    n: int
+
+proc `=copy`(dst: var Foo, src: Foo) =
+  echo "copying"
+  dst.n = src.n
+
+proc `=sink`(dst: var Foo, src: Foo) =
+  echo "sinking"
+  dst.n = src.n
+
+var a: Foo
+
+proc putValue[T](n: T)
+
+proc useForward =
+  putValue(123)
+
+proc putValue[T](n: T) =
+  var b = Foo(n:n)
+  a = b
+  echo b.n
+
+useForward()