make genericParams support static[T] generic params (#13433)

* make genericParams support static[T] generic params

* WrapStatic => StaticParam

lib/pure/typetraits.nim

@@ -86,13 +86,13 @@ since (1, 1):
     # Note: `[]` currently gives: `Error: no generic parameters allowed for ...`
     type(default(T)[i])
 
+  type StaticParam*[value] = object
+    ## used to wrap a static value in `genericParams`
+
 import std/macros
 
-macro genericParams*(T: typedesc): untyped {.since: (1, 1).} =
-  ## return tuple of generic params for generic `T`
-  runnableExamples:
-    type Foo[T1, T2]=object
-    doAssert genericParams(Foo[float, string]) is (float, string)
+macro genericParamsImpl(T: typedesc): untyped =
+  # auxiliary macro needed, can't do it directly in `genericParams`
   result = newNimNode(nnkTupleConstr)
   var impl = getTypeImpl(T)
   expectKind(impl, nnkBracketExpr)
@@ -107,11 +107,33 @@ macro genericParams*(T: typedesc): untyped {.since: (1, 1).} =
         continue
       of nnkBracketExpr:
         for i in 1..<impl.len:
-          result.add impl[i]
+          let ai = impl[i]
+          var ret: NimNode
+          case ai.typeKind
+          of ntyStatic:
+            ret = newTree(nnkBracketExpr, @[bindSym"StaticParam", ai])
+          of ntyTypeDesc:
+            ret = ai
+          else:
+            assert false, $(ai.typeKind, ai.kind)
+          result.add ret
         break
       else:
         error "wrong kind: " & $impl.kind
 
+since (1, 1):
+  template genericParams*(T: typedesc): untyped =
+    ## return tuple of generic params for generic `T`
+    runnableExamples:
+      type Foo[T1, T2]=object
+      doAssert genericParams(Foo[float, string]) is (float, string)
+      type Bar[N: static float, T] = object
+      doAssert genericParams(Bar[1.0, string]) is (StaticParam[1.0], string)
+      doAssert genericParams(Bar[1.0, string]).get(0).value == 1.0
+
+    type T2 = T
+    genericParamsImpl(T2)
+
 when isMainModule:
   static:
     doAssert $type(42) == "int"