New rule to lint against referencing let variables in <template>

[chancancode]

// app/components/foo.gjs
let foo = 1;

function increment() {
  foo++;
}

export default <template>{{foo}}</template>;

This does not "work" – it doesn't error, but it will essentially capture and compile in the value of the foo variable at some arbitrary point and never update again. Even if the component is torn down and a new instance is created/rendered, it will probably still hold on to the old value when the template was initially compiled.

So, generally speaking, one should avoid referencing let variables from within <template> and instead prefer to use const bindings to avoid this confusion/foot-gun.

[patricklx]

Should be easy to implement with #1920