fix(gx): visual selection, expand env vars

---
Rejected experiment: move vim.ui.open() to vim.env.open()

Problem:
`vim.ui` is where user-interface "providers" live, which can be
overridden. It would also be useful to have a "providers" namespace for
platform-specific features such as "open", clipboard, python, and the other
providers listed in `:help providers`. We could overload `vim.ui` to
serve that purpose as the single "providers" namespace, but
`vim.ui.nodejs()` for example seems awkward.

Solution:
`vim.env` currently has too narrow of a purpose. Overload it to also be
a namespace for `vim.env.open`.

diff --git a/runtime/lua/vim/_meta.lua b/runtime/lua/vim/_meta.lua
index 913f1fe20348..17d05ff37595 100644
--- a/runtime/lua/vim/_meta.lua
+++ b/runtime/lua/vim/_meta.lua
@@ -37,8 +37,28 @@ local options_info = setmetatable({}, {
   end,
 })

-vim.env = setmetatable({}, {
-  __index = function(_, k)
+vim.env = setmetatable({
+  open = setmetatable({}, {
+      __call = function(_, uri)
+        print('xxxxx'..uri)
+        return true
+      end,
+      __tostring = function()
+        local v = vim.fn.getenv('open')
+        if v == vim.NIL then
+          return nil
+        end
+        return v
+      end,
+    })
+  },
+  {
+  __index = function(t, k, ...)
+    if k == 'open' then
+      error()
+      -- vim.print({...})
+      -- return rawget(t, k)
+    end
     local v = vim.fn.getenv(k)
     if v == vim.NIL then
       return nil

runtime/lua/vim/lsp/handlers.lua

@@ -576,12 +576,12 @@ M['window/showDocument'] = function(_, result, ctx, _)
 
     local ret = vim.ui.open(uri)
 
-    if ret.code ~= 0 or ret == nil then
+    if ret == nil or ret.code ~= 0 then
       return {
         success = false,
         error = {
           code = protocol.ErrorCodes.UnknownErrorCode,
-          message = ret and ret.stderr or 'No handler could be found',
+          message = ret and ret.stderr or 'No handler found',
         },
       }
     end
@@ -593,7 +593,7 @@ M['window/showDocument'] = function(_, result, ctx, _)
   local client = vim.lsp.get_client_by_id(client_id)
   local client_name = client and client.name or string.format('id=%d', client_id)
   if not client then
-    err_message({ 'LSP[', client_name, '] client has shut down after sending ', ctx.method })
+    err_message('LSP[', client_name, '] client has shut down after sending ', ctx.method)
     return vim.NIL
   end