[core] Fix check for parsing options at top level

This is #1628.

There are non-proc calls like 'source foo.sh a b c' and 'FOO=bar' that
push the stacks in state.Mem().  So we have more subtle logic.

It would be nice if mem.debug_stack had more structured data.  It could
tell us about 'source' vs function calls.  What they have in common is
the argv_stack.

core/state.py

@@ -684,7 +684,7 @@ def set_xtrace(self, b):
   def _SetArrayByNum(self, opt_num, b):
     # type: (int, bool) -> None
     if (opt_num in consts.PARSE_OPTION_NUMS and
-        not self.mem.InGlobalNamespace()):
+        not self.mem.ParsingChangesAllowed()):
       e_die('Syntax options must be set at the top level '
             '(outside any function)')
 
@@ -1331,10 +1331,14 @@ def SetPwd(self, pwd):
     """Used by builtins."""
     self.pwd = pwd
 
-  def InGlobalNamespace(self):
+  def ParsingChangesAllowed(self):
     # type: () -> bool
     """For checking that syntax options are only used at the top level."""
-    return len(self.argv_stack) == 1
+
+    # DISALLOW proc calls     : they push argv_stack, var_stack, debug_stack
+    # ALLOW source foo.sh arg1: pushes argv_stack, debug_stack
+    # ALLOW FOO=bar           : pushes var_stack
+    return len(self.var_stack) == 1 or len(self.argv_stack) == 1
 
   def Dump(self):
     # type: () -> Tuple[Any, Any, Any]

spec/oil-options.test.sh

@@ -779,3 +779,33 @@ common
 status=0
 2 stderr.txt
 ## END
+
+
+#### parse options in sourced file (bug #1628)
+
+set -e  # catch errors
+
+alias e=echo
+shopt -u expand_aliases
+
+source $REPO_ROOT/spec/testdata/parse_opts.sh a b c
+
+echo OK
+
+# alias persists
+e alias on
+
+# parse_paren doesn't persist
+#if (x > 1) {
+#  echo 'OK'
+#}
+
+FOO=bar source $REPO_ROOT/spec/testdata/parse_opts.sh
+echo OK
+
+
+## STDOUT:
+OK
+alias on
+OK
+## END

spec/testdata/parse_opts.sh

@@ -0,0 +1,5 @@
+# Used by spec/oil-options.test.sh
+
+shopt -s parse_paren
+shopt -s expand_aliases
+