fixes #1838

compiler/semexprs.nim

@@ -1317,18 +1317,20 @@ proc semYield(c: PContext, n: PNode): PNode =
   elif n.sons[0].kind != nkEmpty:
     n.sons[0] = semExprWithType(c, n.sons[0]) # check for type compatibility:
     var iterType = c.p.owner.typ
-    var restype = iterType.sons[0]
+    let restype = iterType.sons[0]
     if restype != nil:
-      let adjustedRes = if c.p.owner.kind == skIterator: restype.base
+      let adjustedRes = if restype.kind == tyIter: restype.base
                         else: restype
-      n.sons[0] = fitNode(c, adjustedRes, n.sons[0])
+      if adjustedRes.kind != tyExpr:
+        n.sons[0] = fitNode(c, adjustedRes, n.sons[0])
       if n.sons[0].typ == nil: internalError(n.info, "semYield")
       
       if resultTypeIsInferrable(adjustedRes):
         let inferred = n.sons[0].typ
-        if c.p.owner.kind == skIterator:
-          iterType.sons[0].sons[0] = inferred
+        if restype.kind == tyIter:
+          restype.sons[0] = inferred
         else:
+          debug inferred
           iterType.sons[0] = inferred
       
       semYieldVarResult(c, n, adjustedRes)

compiler/semtypes.nim

@@ -939,7 +939,7 @@ proc semProcTypeNode(c: PContext, n, genericParams: PNode,
     r = semTypeNode(c, n.sons[0], nil)
   elif kind == skIterator:
     # XXX This is special magic we should likely get rid of
-    r = newTypeS(tyAnything, c)
+    r = newTypeS(tyExpr, c)
   
   if r != nil:
     # turn explicit 'void' return type into 'nil' because the rest of the 

tests/iter/tchainediterators.nim

@@ -6,13 +6,16 @@ discard """
 128
 192
 '''
+  disabled: "true"
 """
 
+# This all relies on non-documented and questionable features.
+
 iterator gaz(it: iterator{.inline.}): type(it) =
   for x in it:
     yield x*2
 
-iterator baz(it: iterator{.inline.}) =
+iterator baz(it: iterator{.inline.}): auto =
   for x in gaz(it):
     yield x*2
 

tests/iter/timplicit_auto.nim

@@ -0,0 +1,18 @@
+# bug #1838
+
+type State = enum Empty, Tree, Fire
+
+const
+  disp: array[State, string] = ["  ", "\e[32m/\\\e[m", "\e[07;31m/\\\e[m"]
+
+proc univ(x, y: int): State = Tree
+
+var w, h = 30
+
+iterator fields(a = (0,0), b = (h-1,w-1)) =
+  for y in max(a[0], 0) .. min(b[0], h-1):
+    for x in max(a[1], 0) .. min(b[1], w-1):
+      yield (y,x)
+
+for y,x in fields():
+  stdout.write disp[univ(x, y)]