Refactor closeEmitter to make it more modular (#12365)

compiler/layouter.nim

@@ -160,13 +160,11 @@ proc guidingInd(em: Emitter; pos: int): int =
     inc i
   result = -1
 
-proc closeEmitter*(em: var Emitter) =
+proc renderTokens*(em: var Emitter): string =
+  ## Render Emitter tokens to a string of code
   template defaultCase() =
     content.add em.tokens[i]
     inc lineLen, em.tokens[i].len
-
-  let outFile = em.config.absOutFile
-
   var content = newStringOfCap(16_000)
   var maxLhs = 0
   var lineLen = 0
@@ -243,6 +241,11 @@ proc closeEmitter*(em: var Emitter) =
       defaultCase()
     inc i
 
+  return content
+
+proc writeOut*(em: Emitter, content: string)  =
+  ## Write to disk
+  let outFile = em.config.absOutFile
   if fileExists(outFile) and readFile(outFile.string) == content:
     discard "do nothing, see #9499"
     return
@@ -253,6 +256,11 @@ proc closeEmitter*(em: var Emitter) =
   f.llStreamWrite content
   llStreamClose(f)
 
+proc closeEmitter*(em: var Emitter) =
+  ## Renders emitter tokens and write to a file
+  let content = renderTokens(em)
+  em.writeOut(content)
+
 proc wr(em: var Emitter; x: string; lt: LayoutToken) =
   em.tokens.add x
   em.kinds.add lt