encoding: test that &encoding cannot be changed

Helped-By: Justin M. Keyes <justinkz@gmail.com>

test/functional/ex_cmds/encoding_spec.lua

@@ -0,0 +1,40 @@
+local helpers = require('test.functional.helpers')
+local clear, execute, feed = helpers.clear, helpers.execute, helpers.feed
+local eq, neq, eval = helpers.eq, helpers.neq, helpers.eval
+
+describe('&encoding', function()
+
+  before_each(function()
+    clear()
+    -- sanity check: tests should run with encoding=utf-8
+    eq('utf-8', eval('&encoding'))
+    eq(3, eval('strwidth("Bär")'))
+  end)
+
+  it('cannot be changed after setup', function()
+    execute('set encoding=latin1')
+    -- error message expected
+    feed('<cr>')
+    neq(nil, string.find(eval('v:errmsg'), '^E905:'))
+    eq('utf-8', eval('&encoding'))
+    -- check nvim is still in utf-8 mode
+    eq(3, eval('strwidth("Bär")'))
+  end)
+
+  it('is not changed by `set all&`', function()
+    -- we need to set &encoding to something non-default
+    -- use 'latin1' when enc&vi is 'utf-8', 'utf-8' otherwise
+    execute('set fenc=default')
+    local enc_default, enc_other, width = eval('&fenc'), 'utf-8', 3
+    if enc_default == 'utf-8' then
+      enc_other = 'latin1'
+      width = 4 -- utf-8 string 'Bär' will count as 4 latin1 chars
+    end
+
+    clear('set enc=' .. enc_other)
+    execute('set all&')
+    eq(enc_other, eval('&encoding'))
+    eq(width, eval('strwidth("Bär")'))
+  end)
+
+end)

test/functional/helpers.lua

@@ -183,11 +183,16 @@ local function spawn(argv)
   return session
 end
 
-local function clear()
+local function clear(extra_cmd)
   if session then
     session:exit(0)
   end
-  session = spawn(nvim_argv)
+  local args = {unpack(nvim_argv)}
+  if extra_cmd ~= nil then
+    table.insert(args, '--cmd')
+    table.insert(args, extra_cmd)
+  end
+  session = spawn(args)
 end
 
 local function insert(...)