[osh] Hide string export check behind shopt --set strict_array

Note that bash does NOT respect the "$array is ${array[0]}" rule for

    export FOO
    FOO=(a b c)

It allows it, but nothing is exported.

For Nix compatibility.  Reported by Samuel:

https://oilshell.zulipchat.com/#narrow/stream/307442-nix/topic/Replacing.20bash.20with.20osh.20in.20Nixpkgs.20stdenv

core/state.py

@@ -1666,8 +1666,9 @@ def SetNamed(self, lval, val, which_scopes, flags=0):
 
         if cell.val.tag() not in (value_e.Undef, value_e.Str):
             if cell.exported:
-                # TODO: error context
-                e_die("Only strings can be exported", lval.blame_loc)
+                if self.exec_opts.strict_array():
+                    e_die("Only strings can be exported (strict_array)",
+                          lval.blame_loc)
             if cell.nameref:
                 e_die("nameref must be a string", lval.blame_loc)
 

core/state_test.py

@@ -178,16 +178,11 @@ def testSetVarClearFlag(self):
         self.assertEqual(['1', '2', '3'],
                          mem.var_stack[0]['COMPREPLY'].val.strs)
 
-        # export COMPREPLY
-        try:
-            mem.SetValue(location.LName('COMPREPLY'),
-                         None,
-                         scope_e.Dynamic,
-                         flags=state.SetExport)
-        except error.FatalRuntime as e:
-            pass
-        else:
-            self.fail("Expected failure")
+        # export COMPREPLY - allowed when strict_array not set
+        mem.SetValue(location.LName('COMPREPLY'),
+                     None,
+                     scope_e.Dynamic,
+                     flags=state.SetExport)
 
         # readonly r=1
         mem.SetValue(location.LName('r'),

spec/array.test.sh

@@ -263,13 +263,41 @@ argv.py "${a[@]}"
 # bash parses, but doesn't execute.
 # mksh gives syntax error -- parses differently with 'export'
 # osh no longer parses this statically.
-export PYTHONPATH=(a b c)
-export PYTHONPATH=a  # NOTE: in bash, this doesn't work afterward!
+
+export PYTHONPATH
+
+PYTHONPATH=mystr  # NOTE: in bash, this doesn't work afterward!
 printenv.py PYTHONPATH
-## stdout-json: ""
+
+PYTHONPATH=(myarray)
+printenv.py PYTHONPATH
+
+PYTHONPATH=(a b c)
+printenv.py PYTHONPATH
+
+## status: 0
+## STDOUT:
+mystr
+None
+None
+## END
+
+#### strict_array prevents exporting array
+
+shopt -s strict_array
+
+export PYTHONPATH
+PYTHONPATH=(a b c)
+printenv.py PYTHONPATH
+
 ## status: 1
-## OK bash stdout: None
-## OK bash status: 0
+## STDOUT:
+## END
+
+## N-I bash/mksh status: 0
+## N-I bash/mksh STDOUT:
+None
+## END
 
 #### Arrays can't be used as env bindings
 # Hm bash it treats it as a string!