feature suggestion: {.noredraw.} pragma (#277)

* add {.noredraw.} pragma for event handlers

* put .noredraw. pragma handling in seperate proc

* refactor

* refactor

* Revert "refactor"

This reverts commit 0d4ce4b.

* use result for return

karax/karax.nim

@@ -829,6 +829,14 @@ proc addEventHandler*(n: VNode; k: EventKind; action: proc();
     if not kxi.surpressRedraws: redraw(kxi)
   addEventListener(n, k, wrapper)
 
+proc addEventHandlerNoRedraw*(n: VNode; k: EventKind; action: EventHandler) =
+  addEventListener(n, k, action)
+
+proc addEventHandlerNoRedraw*(n: VNode; k: EventKind; action: proc()) =
+  proc wrapper(ev: Event; n: VNode) =
+    action()
+  addEventListener(n, k, wrapper)
+
 proc setOnHashChange*(action: proc (hashPart: cstring)) {.deprecated: "use setRenderer instead".} =
   ## Now deprecated, instead pass a callback to ``setRenderer`` that receives
   ## a ``data: RouterData`` parameter.

karax/karaxdsl.nim

@@ -1,6 +1,6 @@
 
 import macros, vdom, compact, kbase
-from strutils import startsWith, toLowerAscii
+from strutils import startsWith, toLowerAscii, cmpIgnoreStyle
 
 when defined(js):
   import karax
@@ -44,6 +44,21 @@ proc toKstring(n: NimNode): NimNode =
 proc newDotAsgn(tmp: NimNode, key: string, x: NimNode): NimNode =
   result = newTree(nnkAsgn, newDotExpr(tmp, newIdentNode key), x)
 
+proc handleNoRedrawPragma(call: NimNode, tmpContext, name, anon: NimNode): NimNode =
+  when defined(js):
+    if anon.pragma.kind == nnkPragma and len(anon.pragma) > 0:
+      var hasNoRedrawPragma = false
+      for i in 0 ..< len(anon.pragma):
+        # using anon because anon needs to get rid of the pragma
+        if anon.pragma[i].kind == nnkIdent and cmpIgnoreStyle(anon.pragma[i].strVal, "noredraw") == 0:
+          hasNoRedrawPragma = true
+          anon.pragma.del(i)
+          break
+      if hasNoRedrawPragma:
+        return newCall(ident"addEventHandlerNoRedraw", tmpContext,
+                       newDotExpr(bindSym"EventKind", name), anon)
+  result = call
+
 proc tcall2(n, tmpContext: NimNode): NimNode =
   # we need to distinguish statement and expression contexts:
   # every call statement 's' needs to be transformed to 'dest.add s'.
@@ -94,8 +109,9 @@ proc tcall2(n, tmpContext: NimNode): NimNode =
       if tmpContext == nil:
         error "no VNode to attach the event handler to"
       else:
-        result = newCall(evHandler(), tmpContext,
-                         newDotExpr(bindSym"EventKind", n[0]), anon, ident("kxi"))
+        let call = newCall(evHandler(), tmpContext,
+                           newDotExpr(bindSym"EventKind", n[0]), anon, ident("kxi"))
+        result = handleNoRedrawPragma(call, tmpContext, n[0], anon)
     else:
       result = n
   of nnkVarSection, nnkLetSection, nnkConstSection: