clipboard: adjust v:register when clipboard=unnamed

Helped-By: Nicolas Hillegeer <nicolas@hillegeer.com>
Helped-By: Michael Reed <m.reed@mykolab.com>

src/nvim/normal.c

@@ -914,7 +914,7 @@ getcount:
       && !oap->op_type
       && (idx < 0 || !(nv_cmds[idx].cmd_flags & NV_KEEPREG))) {
     clearop(oap);
-    set_reg_var(0);
+    set_reg_var(get_default_register_name());
   }
 
   /* Get the length of mapped chars again after typing a count, second

src/nvim/ops.c

@@ -5310,7 +5310,28 @@ static void free_register(struct yankreg *reg)
   y_current = curr;
 }
 
-// return target register
+/// Check if the default register (used in an unnamed paste) should be a
+/// clipboard register. This happens when `clipboard=unnamed[plus]` is set
+/// and a provider is available.
+///
+/// @returns the name of of a clipboard register that should be used, or `NUL` if none.
+int get_default_register_name(void)
+{
+  int name = NUL;
+  adjust_clipboard_name(&name, true, false);
+  return name;
+}
+
+/// Determine if register `*name` should be used as a clipboard.
+/// In an unnammed operation, `*name` is `NUL` and will be adjusted to `'*'/'+'` if
+/// `clipboard=unnamed[plus]` is set.
+///
+/// @param name The name of register, or `NUL` if unnamed.
+/// @param quiet Suppress error messages
+/// @param writing if we're setting the contents of the clipboard
+///
+/// @returns the yankreg that should be used, or `NULL`
+/// if the register isn't a clipboard or provider isn't available.
 static struct yankreg* adjust_clipboard_name(int *name, bool quiet, bool writing) {
   if (*name == '*' || *name == '+') {
     if(!eval_has_provider("clipboard")) {

test/functional/clipboard/clipboard_provider_spec.lua

@@ -72,6 +72,7 @@ end
 describe('the unnamed register', function()
   before_each(clear)
   it('works without provider', function()
+    eq('"', eval('v:register'))
     basic_register_test()
   end)
 end)
@@ -227,6 +228,13 @@ describe('clipboard usage', function()
         a line]])
     end)
 
+    it('supports v:register and getreg() without parameters', function()
+      eq('*', eval('v:register'))
+      execute("let g:test_clip['*'] = [['some block',''], 'b']")
+      eq('some block', eval('getreg()'))
+      eq('\02210', eval('getregtype()'))
+    end)
+
   end)
 
   it('supports :put', function()