put the new for loop macros under an experimental switch named 'forLo…

…opMacros'

compiler/options.nim

@@ -111,14 +111,16 @@ type
  ideNone, ideSug, ideCon, ideDef, ideUse, ideDus, ideChk, ideMod,
  ideHighlight, ideOutline, ideKnown, ideMsg
 
- Feature* = enum ## experimental features
+ Feature* = enum ## experimental features; DO NOT RENAME THESE!
  implicitDeref,
  dotOperators,
  callOperator,
  parallel,
  destructor,
  notnil,
- dynamicBindSym
+ dynamicBindSym,
+ forLoopMacros
+ #caseStmtMacros
 
  SymbolFilesOption* = enum
  disabledSf, writeOnlySf, readOnlySf, v2Sf

compiler/semstmts.nim

@@ -720,8 +720,9 @@ proc handleForLoopMacro(c: PContext; n: PNode): PNode =
 proc semFor(c: PContext, n: PNode): PNode =
  checkMinSonsLen(n, 3, c.config)
  var length = sonsLen(n)
- result = handleForLoopMacro(c, n)
- if result != nil: return result
+ if forLoopMacros in c.features:
+ result = handleForLoopMacro(c, n)
+ if result != nil: return result
  openScope(c)
  result = n
  n.sons[length-2] = semExprNoDeref(c, n.sons[length-2], {efWantIterator})

doc/manual.rst

@@ -5380,6 +5380,7 @@ type ``system.ForLoopStmt`` can rewrite the entirety of a ``for`` loop:
  :test: "nim c $1"
 
  import macros
+ {.experimental: "forLoopMacros".}
 
  macro enumerate(x: ForLoopStmt): untyped =
  expectKind x, nnkForStmt
@@ -5406,6 +5407,10 @@ type ``system.ForLoopStmt`` can rewrite the entirety of a ``for`` loop:
  echo a2, " ", b2
 
 
+Currently for loop macros must be enabled explicitly
+via ``{.experimental: "forLoopMacros".}``.
+
+
 Special Types
 =============
 

tests/macros/tforloop_macro1.nim

@@ -12,7 +12,7 @@ discard """
 """
 
 import macros
-
+{.experimental: "forLoopMacros".}
 macro mymacro(): untyped =
  result = newLit([1, 2, 3])