fixes #2585

compiler/parampatterns.nim

@@ -184,7 +184,7 @@ proc isAssignable*(owner: PSym, n: PNode): TAssignableResult =
   case n.kind
   of nkSym:
     # don't list 'skLet' here:
-    if n.sym.kind in {skVar, skResult, skTemp}:
+    if n.sym.kind in {skVar, skResult, skTemp, skParam}:
       if owner != nil and owner.id == n.sym.owner.id and
           sfGlobal notin n.sym.flags:
         result = arLocalLValue

compiler/semdata.nim

@@ -118,7 +118,6 @@ proc newOptionEntry*(): POptionEntry
 proc newLib*(kind: TLibKind): PLib
 proc addToLib*(lib: PLib, sym: PSym)
 proc makePtrType*(c: PContext, baseType: PType): PType
-proc makeVarType*(c: PContext, baseType: PType): PType
 proc newTypeS*(kind: TTypeKind, c: PContext): PType
 proc fillTypeS*(dest: PType, kind: TTypeKind, c: PContext)
 
@@ -213,9 +212,12 @@ proc makePtrType(c: PContext, baseType: PType): PType =
   result = newTypeS(tyPtr, c)
   addSonSkipIntLit(result, baseType.assertNotNil)
 
-proc makeVarType(c: PContext, baseType: PType): PType =
-  result = newTypeS(tyVar, c)
-  addSonSkipIntLit(result, baseType.assertNotNil)
+proc makeVarType*(c: PContext, baseType: PType): PType =
+  if baseType.kind == tyVar:
+    result = baseType
+  else:
+    result = newTypeS(tyVar, c)
+    addSonSkipIntLit(result, baseType.assertNotNil)
 
 proc makeTypeDesc*(c: PContext, typ: PType): PType =
   result = newTypeS(tyTypeDesc, c)

tests/template/tstmt_semchecked_twice.nim

@@ -0,0 +1,30 @@
+
+# bug #2585
+
+type
+    RenderPass = object
+       state: ref int
+
+    RenderData* = object
+        fb: int
+        walls: seq[RenderPass]
+
+    Mat2 = int
+    Vector2[T] = T
+    Pixels=int
+
+template use*(fb: int, st: stmt) : stmt =
+    echo "a ", $fb
+    st
+    echo "a ", $fb
+
+proc render(rdat: var RenderData; passes: var openarray[RenderPass]; proj: Mat2;
+            indexType = 1) =
+    for i in 0 .. <len(passes):
+        echo "blah ", repr(passes[i])
+
+
+
+proc render2*(rdat: var RenderData; screenSz: Vector2[Pixels]; proj: Mat2) =
+    use rdat.fb:
+        render(rdat, rdat.walls, proj, 1)