My supported-only-by-vibes take is that when a user writes {a: 1, b: 2} they are far more likely to be typoing either a map literal (missing %) or a kwlist literal (wrong kind of bracket).

Looking at Syntax reference — Elixir v1.20.2 I’m wondering if the syntax sugar in tuples should rather be removed. The atom shorthand within […] and %{…} works the same, but is considered a feature available for both those types and is not available for tuples.

The syntax sugar for skipping square brackets is documented to apply for the last parameter of calls. Creating a tuple is not a call. The closest comparison to the creation of a tuple would be the creation of a binary <<…>>.

@gregvaughn Yes, it’s indeed confusing - the syntax, see:

iex> {:do_something, a: 1, b: 2}
{:do_something, [a: 1, b: 2]}
iex> {a: 1, b: 2}
** (SyntaxError) invalid syntax found on iex:2:1:
    error: unexpected keyword list inside tuple. Did you mean to write a map (using %{...}) or a list (using [...]) instead? Syntax error after: '{'
    │
  2 │ {a: 1, b: 2}
    │ ^
    │
    └─ iex:2:1
    (iex 1.17.0-rc.1) lib/iex/evaluator.ex:295: IEx.Evaluator.parse_eval_inspect/4
    (iex 1.17.0-rc.1) lib/iex/evaluator.ex:187: IEx.Evaluator.loop/1
    (iex 1.17.0-rc.1) lib/iex/evaluator.ex:32: IEx.Evaluator.init/5
    (stdlib 6.0) proc_lib.erl:329: :proc_lib.init_p_do_apply/3

How about something like this?
<div {:class, button: true, "button-active": false}></div>