fix(clipboard): make getreg() accurate for clipboard registers (#26740)

Problem:  getreg("*") / getreg("+") disagree with :registers.
Solution: Avoid falling back to unnamed register if provider fails.

2 files changed, 15 insertions, 2 deletions

diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index 8dc267cc45..4cce2e7ba6 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -815,9 +815,15 @@ yankreg_T *get_yank_register(int regname, int mode)
 {
   yankreg_T *reg;
 
-  if (mode == YREG_PASTE && get_clipboard(regname, &reg, false)) {
+  if ((mode == YREG_PASTE || mode == YREG_PUT)
+      && get_clipboard(regname, &reg, false)) {
     // reg is set to clipboard contents.
     return reg;
+  } else if (mode == YREG_PUT && (regname == '*' || regname == '+')) {
+    // in case clipboard not available and we aren't actually pasting,
+    // return an empty register
+    static yankreg_T empty_reg = { .y_array = NULL };
+    return &empty_reg;
   } else if (mode != YREG_YANK
              && (regname == 0 || regname == '"' || regname == '*' || regname == '+')
              && y_previous != NULL) {
@@ -4893,7 +4899,7 @@ void *get_reg_contents(int regname, int flags)
     return get_reg_wrap_one_line(xstrdup(retval), flags);
   }
 
-  yankreg_T *reg = get_yank_register(regname, YREG_PASTE);
+  yankreg_T *reg = get_yank_register(regname, YREG_PUT);
   if (reg->y_array == NULL) {
     return NULL;
   }
diff --git a/test/functional/provider/clipboard_spec.lua b/test/functional/provider/clipboard_spec.lua
index 3c2e358745..004ee6d106 100644
--- a/test/functional/provider/clipboard_spec.lua
+++ b/test/functional/provider/clipboard_spec.lua
@@ -752,4 +752,11 @@ describe('clipboard (with fake clipboard.vim)', function()
     expect('some some')
     eq('some', eval('getreg("*")'))
   end)
+
+  it('does not fall back to unnamed register with getreg() #24257', function ()
+    eval('setreg("", "wrong")')
+    command('let g:cliperror = 1')
+    eq('', eval('getreg("*")'))
+    eq('', eval('getreg("+")'))
+  end)
 end)