added system.typeof operation; fixes #9093

lib/pure/collections/sequtils.nim

@@ -673,10 +673,16 @@ template mapIt*(s: typed, op: untyped): untyped =
   ##     nums = @[1, 2, 3, 4]
   ##     strings = nums.mapIt($(4 * it))
   ##   assert strings == @["4", "8", "12", "16"]
-  type outType = type((
-    block:
-      var it{.inject.}: type(items(s));
-      op))
+  when defined(nimHasTypeof):
+    type outType = typeof((
+      block:
+        var it{.inject.}: typeof(items(s), typeOfIter);
+        op), typeOfProc)
+  else:
+    type outType = type((
+      block:
+        var it{.inject.}: type(items(s));
+        op))
   when compiles(s.len):
     block: # using a block avoids https://github.com/nim-lang/Nim/issues/8580
 
@@ -1135,5 +1141,13 @@ when isMainModule:
       A, B
     doAssert mapIt(X, $it) == @["A", "B"]
 
+  block:
+    # bug #9093
+    let inp = "a:b,c:d"
+
+    let outp = inp.split(",").mapIt(it.split(":"))
+    doAssert outp == @[@["a", "b"], @["c", "d"]]
+
+
   when not defined(testing):
     echo "Finished doc tests"

lib/system.nim

@@ -180,6 +180,15 @@ else:
     ## Cannot be overloaded.
     discard
 
+when defined(nimHasTypeof):
+  type
+    TypeOfMode* = enum ## Possible modes of `typeof`.
+      typeOfProc,      ## Prefer the interpretation that means `x` is a proc call.
+      typeOfIter       ## Prefer the interpretation that means `x` is an iterator call.
+  proc typeof*(x: untyped; mode = typeOfIter): typeDesc {.magic: "TypeOf", noSideEffect, compileTime.} =
+    ## Builtin 'typeof' operation for accessing the type of an expression. Since version 0.20.0.
+    discard
+
 proc `not`*(x: bool): bool {.magic: "Not", noSideEffect.}
   ## Boolean not; returns true iff ``x == false``.