vim-patch:8.2.1794: no falsy Coalescing operator

Problem:    No falsy Coalescing operator.
Solution:   Add the "??" operator.  Fix mistake with function argument count.

https://github.com/vim/vim/commit/92f26c256e06277ff2ec4ce7adea1eb58c85abe0

Cherry-pick tv2bool() into eval/typval.c.
Cherry-pick *??* tag from Vim runtime.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index 3e67571053..91be41751e 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -4201,3 +4201,34 @@ const char *tv_get_string_buf(const typval_T *const tv, char *const buf)
 
   return res != NULL ? res : "";
 }
+
+/// Return true when "tv" is not falsy: non-zero, non-empty string, non-empty
+/// list, etc.  Mostly like what JavaScript does, except that empty list and
+/// empty dictionary are false.
+bool tv2bool(const typval_T *const tv)
+{
+  switch (tv->v_type) {
+  case VAR_NUMBER:
+    return tv->vval.v_number != 0;
+  case VAR_FLOAT:
+    return tv->vval.v_float != 0.0;
+  case VAR_PARTIAL:
+    return tv->vval.v_partial != NULL;
+  case VAR_FUNC:
+  case VAR_STRING:
+    return tv->vval.v_string != NULL && *tv->vval.v_string != NUL;
+  case VAR_LIST:
+    return tv->vval.v_list != NULL && tv->vval.v_list->lv_len > 0;
+  case VAR_DICT:
+    return tv->vval.v_dict != NULL && tv->vval.v_dict->dv_hashtab.ht_used > 0;
+  case VAR_BOOL:
+    return tv->vval.v_bool == kBoolVarTrue;
+  case VAR_SPECIAL:
+    return tv->vval.v_special == kSpecialVarNull;
+  case VAR_BLOB:
+    return tv->vval.v_blob != NULL && tv->vval.v_blob->bv_ga.ga_len > 0;
+  case VAR_UNKNOWN:
+    break;
+  }
+  return false;
+}