Fixes 10202 (#10283)

* Add a test case for #10202
* Fix asgn for object tyVars; fixes #10202
* Check the variant kind before accessing the sym field

compiler/jsgen.nim

@@ -925,7 +925,7 @@ const
 
 proc needsNoCopy(p: PProc; y: PNode): bool =
   return y.kind in nodeKindsNeedNoCopy or
-        ((mapType(y.typ) != etyBaseIndex or y.sym.kind == skParam) and
+        ((mapType(y.typ) != etyBaseIndex or (y.kind == nkSym and y.sym.kind == skParam)) and
           (skipTypes(y.typ, abstractInst).kind in
             {tyRef, tyPtr, tyLent, tyVar, tyCString, tyProc} + IntegralTypes))
 
@@ -950,7 +950,7 @@ proc genAsgnAux(p: PProc, x, y: PNode, noCopyNeeded: bool) =
       lineF(p, "$1 = nimCopy(null, $2, $3);$n",
                [a.rdLoc, b.res, genTypeInfo(p, y.typ)])
   of etyObject:
-    if (needsNoCopy(p, y) and needsNoCopy(p, x)) or noCopyNeeded:
+    if x.typ.kind == tyVar or (needsNoCopy(p, y) and needsNoCopy(p, x)) or noCopyNeeded:
       lineF(p, "$1 = $2;$n", [a.rdLoc, b.rdLoc])
     else:
       useMagic(p, "nimCopy")

tests/js/t9410.nim

@@ -1,13 +1,3 @@
-template doAssert(exp: untyped) =
-  when defined(echot9410):
-    let r = exp
-    echo $(instantiationInfo().line) & ":\n  " & astToStr(exp) & "\n  was " & repr(r)
-    when not defined(noassertt9410):
-      system.doAssert r
-  else:
-    when not defined(noassertt9410):
-      system.doAssert exp
-
 template tests =
   block:
     var i = 0
@@ -429,6 +419,33 @@ template tests =
     let xptr2 = cast[type(xptr)](p2)
     doAssert xptr == xptr2
   
+  block: # var types
+    block t10202:
+      type Point = object
+        x: float
+        y: float
+
+      var points: seq[Point]
+
+      points.add(Point(x:1, y:2))
+
+      for i, p in points.mpairs:
+        p.x += 1
+
+      doAssert points[0].x == 2
+    
+    block:
+      var ints = @[1, 2, 3]
+      for i, val in mpairs ints:
+        val *= 10
+      doAssert ints == @[10, 20, 30]
+    
+    block:
+      var seqOfSeqs = @[@[1, 2], @[3, 4]]
+      for i, val in mpairs seqOfSeqs:
+        val[0] *= 10
+      doAssert seqOfSeqs == @[@[10, 2], @[30, 4]]
+
   when false:
     block: # openarray
           # Error: internal error: genAddr: nkStmtListExpr