feat(ui): restore has('gui_running')

Problem:
has('gui_running') is still common in the wild and our answer has
changed over time, causing frustration.
https://github.com/vimpostor/vim-tpipeline/commit/95a6ccbe9f33bc42dd4cee45731d8bc3fbcd92d1

Solution:
Use stdin_tty/stdout_tty to decide if a UI is (not) a GUI.

1 files changed, 19 insertions, 2 deletions

diff --git a/test/functional/vimscript/has_spec.lua b/test/functional/vimscript/has_spec.lua
index 2e26d603b3..78a761d370 100644
--- a/test/functional/vimscript/has_spec.lua
+++ b/test/functional/vimscript/has_spec.lua
@@ -1,8 +1,11 @@
 local helpers = require('test.functional.helpers')(after_each)
-local eq = helpers.eq
+local Screen = require('test.functional.ui.screen')
 local clear = helpers.clear
+local connect = helpers.connect
+local eq = helpers.eq
 local funcs = helpers.funcs
 local is_os = helpers.is_os
+local nvim_prog = helpers.nvim_prog
 
 describe('has()', function()
   before_each(clear)
@@ -69,8 +72,22 @@ describe('has()', function()
     end
   end)
 
+  it('"gui_running"', function()
+    eq(0, funcs.has('gui_running'))
+    local tui = Screen.new(50,15)
+    local gui_session = connect(funcs.serverstart())
+    local gui = Screen.new(50,15)
+    eq(0, funcs.has('gui_running'))
+    tui:attach({ext_linegrid=true, rgb=true, stdin_tty=true, stdout_tty=true})
+    gui:attach({ext_multigrid=true, rgb=true}, gui_session)
+    eq(1, funcs.has('gui_running'))
+    tui:detach()
+    eq(1, funcs.has('gui_running'))
+    gui:detach()
+    eq(0, funcs.has('gui_running'))
+  end)
+
   it('does not change v:shell_error', function()
-    local nvim_prog = helpers.nvim_prog
     funcs.system({nvim_prog, '-es', '+73cquit'})
     funcs.has('python3') -- use a call whose implementation shells out
     eq(73, funcs.eval('v:shell_error'))