[spec/ysh-json] Add failing test case

We're doing reference counting, not cycle detection!  In both JSON and
ASDL.

[ASDL] Fix type annotations in generated Python.

asdl/gen_python.py

@@ -385,7 +385,7 @@ def _GenClass(self,
         #
 
         self.Emit('  def PrettyTree(self, trav=None):')
-        self.Emit('    # type: (TraversalState) -> hnode_t')
+        self.Emit('    # type: (Optional[TraversalState]) -> hnode_t')
         self.Emit('    trav = trav or TraversalState()')
         self.Emit('    heap_id = id(self)')
         self.Emit('    if heap_id in trav.seen:')
@@ -412,7 +412,7 @@ def _GenClass(self,
         #
 
         self.Emit('  def _AbbreviatedTree(self, trav=None):')
-        self.Emit('    # type: (TraversalState) -> hnode_t')
+        self.Emit('    # type: (Optional[TraversalState]) -> hnode_t')
         self.Emit('    trav = trav or TraversalState()')
         self.Emit('    heap_id = id(self)')
         self.Emit('    if heap_id in trav.seen:')
@@ -431,7 +431,7 @@ def _GenClass(self,
         self.Emit('')
 
         self.Emit('  def AbbreviatedTree(self, trav=None):')
-        self.Emit('    # type: (TraversalState) -> hnode_t')
+        self.Emit('    # type: (Optional[TraversalState]) -> hnode_t')
         abbrev_name = '_%s' % class_name
         if abbrev_name in self.abbrev_mod_entries:
             self.Emit('    p = %s(self)' % abbrev_name)

doc/pretty-printing.md

@@ -114,7 +114,14 @@ Identical to the dynamically typed case above.
 ## TODO
 
 - Fix ADSL cycle bug
+  - Fix it in C++
+
+- distinguish ... vs ---
+
 - Somehow do ASDL ref counts, because the thing is long
+  - to fix bin/osh -n
+
+
 - Write separate parser for TYG8
   - no commas, no JSON8, just () and []
     - (unquotedyaks unquotedjs:value) and [value value]

spec/ysh-builtin-meta.test.sh

@@ -1,4 +1,4 @@
-## oils_failures_allowed: 2
+## oils_failures_allowed: 1
 
 #### pp asdl
 

spec/ysh-json.test.sh

@@ -1,4 +1,4 @@
-## oils_failures_allowed: 2
+## oils_failures_allowed: 3
 ## tags: dev-minimal
 
 #### usage errors
@@ -237,6 +237,20 @@ echo 'should have failed'
 1:{ ...
 ## END
 
+#### json write of List/Dict referenced twice (bug fix)
+
+var mylist = [1,2,3]
+var mydict = {foo: "bar"}
+
+var top = {k: mylist, k2: mylist, k3: mydict, k4: mydict}
+
+# BUG!
+json write (top)
+
+## STDOUT:
+## END
+
+
 #### json read doesn't accept u'' or b'' strings
 
 json read <<EOF