Fix usage of parameters types in templates #6756 (#6768)

compiler/evaltempl.nim

@@ -42,7 +42,7 @@ proc evalTemplateAux(templ, actual: PNode, c: var TemplCtx, result: PNode) =
            s.kind == skType and s.typ != nil and s.typ.kind == tyGenericParam:
         handleParam actual.sons[s.owner.typ.len + s.position - 1]
       else:
-        internalAssert sfGenSym in s.flags
+        internalAssert sfGenSym in s.flags or s.kind == skType
         var x = PSym(idTableGet(c.mapping, s))
         if x == nil:
           x = copySym(s, false)

tests/ccgbugs/t6756.nim

@@ -0,0 +1,18 @@
+import typetraits
+type
+  A[T] = ref object
+    v: T
+
+template templ(o: A, op: untyped): untyped =
+  type T = type(o.v)
+
+  var res: A[T]
+
+  block:
+    var it {.inject.}: T
+    it = o.v
+    res = A[T](v: op)
+  res
+
+let a = A[int](v: 1)
+echo templ(a, it + 2)[]