*: Provide list length when allocating lists

3 files changed, 52 insertions, 17 deletions

diff --git a/src/nvim/eval/decode.c b/src/nvim/eval/decode.c
index af4e055d23..c729d00ae7 100644
--- a/src/nvim/eval/decode.c
+++ b/src/nvim/eval/decode.c
@@ -150,7 +150,7 @@ static inline int json_decoder_pop(ValuesStackItem obj,
       }
       obj_di->di_tv = obj.val;
     } else {
-      list_T *const kv_pair = tv_list_alloc();
+      list_T *const kv_pair = tv_list_alloc(2);
       tv_list_append_list(last_container.special_val, kv_pair);
       tv_list_append_owned_tv(kv_pair, key.val);
       tv_list_append_owned_tv(kv_pair, obj.val);
@@ -221,13 +221,18 @@ static inline int json_decoder_pop(ValuesStackItem obj,
 /// Create a new special dictionary that ought to represent a MAP
 ///
 /// @param[out]  ret_tv  Address where new special dictionary is saved.
+/// @param[in]  len  Expected number of items to be populated before list
+///                  becomes accessible from VimL. It is still valid to
+///                  underpopulate a list, value only controls how many elements
+///                  will be allocated in advance. @see ListLenSpecials.
 ///
 /// @return [allocated] list which should contain key-value pairs. Return value
 ///                     may be safely ignored.
-list_T *decode_create_map_special_dict(typval_T *const ret_tv)
+list_T *decode_create_map_special_dict(typval_T *const ret_tv,
+                                       const ptrdiff_t len)
   FUNC_ATTR_NONNULL_ALL
 {
-  list_T *const list = tv_list_alloc();
+  list_T *const list = tv_list_alloc(len);
   tv_list_ref(list);
   create_special_dict(ret_tv, kMPMap, ((typval_T) {
     .v_type = VAR_LIST,
@@ -263,7 +268,7 @@ typval_T decode_string(const char *const s, const size_t len,
                               ? ((s != NULL) && (memchr(s, NUL, len) != NULL))
                               : (bool)hasnul);
   if (really_hasnul) {
-    list_T *const list = tv_list_alloc();
+    list_T *const list = tv_list_alloc(kListLenMayKnow);
     tv_list_ref(list);
     typval_T tv;
     create_special_dict(&tv, binary ? kMPBinary : kMPString, ((typval_T) {
@@ -843,7 +848,7 @@ json_decode_string_cycle_start:
         break;
       }
       case '[': {
-        list_T *list = tv_list_alloc();
+        list_T *list = tv_list_alloc(kListLenMayKnow);
         tv_list_ref(list);
         typval_T tv = {
           .v_type = VAR_LIST,
@@ -864,7 +869,7 @@ json_decode_string_cycle_start:
         list_T *val_list = NULL;
         if (next_map_special) {
           next_map_special = false;
-          val_list = decode_create_map_special_dict(&tv);
+          val_list = decode_create_map_special_dict(&tv, kListLenMayKnow);
         } else {
           dict_T *dict = tv_dict_alloc();
           dict->dv_refcount++;
@@ -964,7 +969,7 @@ int msgpack_to_vim(const msgpack_object mobj, typval_T *const rettv)
           .vval = { .v_number = (varnumber_T) mobj.via.u64 },
         };
       } else {
-        list_T *const list = tv_list_alloc();
+        list_T *const list = tv_list_alloc(4);
         tv_list_ref(list);
         create_special_dict(rettv, kMPInteger, ((typval_T) {
           .v_type = VAR_LIST,
@@ -987,7 +992,7 @@ int msgpack_to_vim(const msgpack_object mobj, typval_T *const rettv)
           .vval = { .v_number = (varnumber_T) mobj.via.i64 },
         };
       } else {
-        list_T *const list = tv_list_alloc();
+        list_T *const list = tv_list_alloc(4);
         tv_list_ref(list);
         create_special_dict(rettv, kMPInteger, ((typval_T) {
           .v_type = VAR_LIST,
@@ -1033,7 +1038,7 @@ int msgpack_to_vim(const msgpack_object mobj, typval_T *const rettv)
       break;
     }
     case MSGPACK_OBJECT_ARRAY: {
-      list_T *const list = tv_list_alloc();
+      list_T *const list = tv_list_alloc((ptrdiff_t)mobj.via.array.size);
       tv_list_ref(list);
       *rettv = (typval_T) {
         .v_type = VAR_LIST,
@@ -1085,9 +1090,10 @@ int msgpack_to_vim(const msgpack_object mobj, typval_T *const rettv)
       }
       break;
 msgpack_to_vim_generic_map: {}
-      list_T *const list = decode_create_map_special_dict(rettv);
+      list_T *const list = decode_create_map_special_dict(
+          rettv, (ptrdiff_t)mobj.via.map.size);
       for (size_t i = 0; i < mobj.via.map.size; i++) {
-        list_T *const kv_pair = tv_list_alloc();
+        list_T *const kv_pair = tv_list_alloc(2);
         tv_list_append_list(list, kv_pair);
 
         typval_T key_tv = { .v_type = VAR_UNKNOWN };
@@ -1107,10 +1113,10 @@ msgpack_to_vim_generic_map: {}
       break;
     }
     case MSGPACK_OBJECT_EXT: {
-      list_T *const list = tv_list_alloc();
+      list_T *const list = tv_list_alloc(2);
       tv_list_ref(list);
       tv_list_append_number(list, mobj.via.ext.type);
-      list_T *const ext_val_list = tv_list_alloc();
+      list_T *const ext_val_list = tv_list_alloc(kListLenMayKnow);
       tv_list_append_list(list, ext_val_list);
       create_special_dict(rettv, kMPExt, ((typval_T) {
         .v_type = VAR_LIST,
diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index ac6c8c8aa6..6f829be0b4 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -132,8 +132,14 @@ void tv_list_watch_fix(list_T *const l, const listitem_T *const item)
 ///
 /// Caller should take care of the reference count.
 ///
+/// @param[in]  len  Expected number of items to be populated before list
+///                  becomes accessible from VimL. It is still valid to
+///                  underpopulate a list, value only controls how many elements
+///                  will be allocated in advance. Currently does nothing.
+///                  @see ListLenSpecials.
+///
 /// @return [allocated] new list.
-list_T *tv_list_alloc(void)
+list_T *tv_list_alloc(const ptrdiff_t len)
   FUNC_ATTR_NONNULL_RET
 {
   list_T *const list = xcalloc(1, sizeof(list_T));
@@ -521,7 +527,7 @@ list_T *tv_list_copy(const vimconv_T *const conv, list_T *const orig,
     return NULL;
   }
 
-  list_T *copy = tv_list_alloc();
+  list_T *copy = tv_list_alloc(tv_list_len(orig));
   tv_list_ref(copy);
   if (copyID != 0) {
     // Do this before adding the items, because one of the items may
@@ -1817,12 +1823,16 @@ void tv_dict_set_keys_readonly(dict_T *const dict)
 /// Also sets reference count.
 ///
 /// @param[out]  ret_tv  Structure where list is saved.
+/// @param[in]  len  Expected number of items to be populated before list
+///                  becomes accessible from VimL. It is still valid to
+///                  underpopulate a list, value only controls how many elements
+///                  will be allocated in advance. @see ListLenSpecials.
 ///
 /// @return [allocated] pointer to the created list.
-list_T *tv_list_alloc_ret(typval_T *const ret_tv)
+list_T *tv_list_alloc_ret(typval_T *const ret_tv, const ptrdiff_t len)
   FUNC_ATTR_NONNULL_ALL
 {
-  list_T *const l = tv_list_alloc();
+  list_T *const l = tv_list_alloc(len);
   ret_tv->vval.v_list = l;
   ret_tv->v_type = VAR_LIST;
   ret_tv->v_lock = VAR_UNLOCKED;
diff --git a/src/nvim/eval/typval.h b/src/nvim/eval/typval.h
index c9a9a3e7e8..3993a384d2 100644
--- a/src/nvim/eval/typval.h
+++ b/src/nvim/eval/typval.h
@@ -31,6 +31,25 @@ typedef double float_T;
 /// Refcount for dict or list that should not be freed
 enum { DO_NOT_FREE_CNT = (INT_MAX / 2) };
 
+/// Additional values for tv_list_alloc() len argument
+enum {
+  /// List length is not known in advance
+  ///
+  /// To be used when there is neither a way to know how many elements will be
+  /// needed nor are any educated guesses.
+  kListLenUnknown = -1,
+  /// List length *should* be known, but is actually not
+  ///
+  /// All occurrences of this value should be eventually removed. This is for
+  /// the case when the only reason why list length is not known is that it
+  /// would be hard to code without refactoring, but refactoring is needed.
+  kListLenShouldKnow = -2,
+  /// List length may be known in advance, but it requires too much effort
+  ///
+  /// To be used when it looks impractical to determine list length.
+  kListLenMayKnow = -3,
+} ListLenSpecials;
+
 /// Maximal possible value of varnumber_T variable
 #define VARNUMBER_MAX INT64_MAX
 #define UVARNUMBER_MAX UINT64_MAX