feat(lua): add Iter:unique() (#37592)

runtime/lua/vim/_core/ex_cmd.lua

@@ -10,13 +10,13 @@ end
 
 --- @return string[]
 local function get_client_names()
-  local client_names = vim
+  return vim
     .iter(lsp.get_clients())
     :map(function(client)
       return client.name
     end)
+    :unique()
     :totable()
-  return vim.list.unique(client_names)
 end
 
 --- @return string[]
@@ -34,7 +34,8 @@ local function get_config_names()
   vim.list_extend(config_names, vim.tbl_keys(lsp.config._configs))
 
   return vim
-    .iter(vim.list.unique(config_names))
+    .iter(config_names)
+    :unique()
     --- @param name string
     :filter(function(name)
       return name ~= '*'

runtime/lua/vim/_core/shared.lua

@@ -365,9 +365,11 @@ end
 --- Only the first occurrence of each value is kept.
 --- The operation is performed in-place and the input table is modified.
 ---
---- Accepts an optional `key` argument that if provided is called for each
+--- Accepts an optional `key` argument, which if provided is called for each
 --- value in the list to compute a hash key for uniqueness comparison.
 --- This is useful for deduplicating table values or complex objects.
+--- If `key` returns `nil` for a value, that value will be considered unique,
+--- even if multiple values return `nil`.
 ---
 --- Example:
 --- ```lua
@@ -385,6 +387,7 @@ end
 --- @param t T[]
 --- @param key? fun(x: T): any Optional hash function to determine uniqueness of values
 --- @return T[] : The deduplicated list
+--- @see |Iter:unique()|
 function vim.list.unique(t, key)
   vim.validate('t', t, 'table')
   local seen = {} --- @type table<any,boolean>