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

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

@@ -720,6 +720,7 @@ proc handleForLoopMacro(c: PContext; n: PNode): PNode =
 proc semFor(c: PContext, n: PNode): PNode =
   checkMinSonsLen(n, 3, c.config)
   var length = sonsLen(n)
+  if forLoopMacros in c.features:
     result = handleForLoopMacro(c, n)
     if result != nil: return result
   openScope(c)

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])