fix #11634 (#21146)

(cherry picked from commit ca9c74391a)

compiler/semstmts.nim

@@ -687,9 +687,12 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
         if v.kind == skLet and sfImportc notin v.flags:
           localError(c.config, a.info, errLetNeedsInit)
       if sfCompileTime in v.flags:
-        var x = newNodeI(result.kind, v.info)
-        x.add result[i]
-        vm.setupCompileTimeVar(c.module, c.idgen, c.graph, x)
+        if a.kind != nkVarTuple:
+          var x = newNodeI(result.kind, v.info)
+          x.add result[i]
+          vm.setupCompileTimeVar(c.module, c.idgen, c.graph, x)
+        else:
+          localError(c.config, a.info, "cannot destructure to compile time variable")
       if v.flags * {sfGlobal, sfThread} == {sfGlobal}:
         message(c.config, v.info, hintGlobalVar)
       if {sfGlobal, sfPure} <= v.flags:

tests/misc/t11634.nim

@@ -0,0 +1,20 @@
+discard """
+  action: reject
+  nimout: '''
+t11634.nim(20, 7) Error: cannot destructure to compile time variable
+'''
+"""
+
+type Foo = ref object
+  val: int
+
+proc divmod(a, b: Foo): (Foo, Foo) =
+  (
+    Foo(val: a.val div b.val),
+    Foo(val: a.val mod b.val)
+  )
+
+block:
+  let a {.compileTime.} = Foo(val: 2)
+  let b {.compileTime.} = Foo(val: 3)
+  let (c11634 {.compileTime.}, d11634 {.compileTime.}) = divmod(a, b)