E0152: A template file declares no struct above its markup

A .vuka.html file is one struct and its markup: the struct is declared in the file's <script lang="go">, with its hooks and methods, and the markup below is its view. The file starts with its markup instead, its struct declared in a .go or .vuka file beside it, so the two have to be kept in step by hand.

Move the struct's declaration, its decorated hooks and its methods into the header; the types it uses that aren't rendered — a form's input, an enum — stay in logic files.

Wrong

// counter.go
package components

type Counter struct {
	ui.Live
	n int
}

func (c *Counter) Inc() { c.n++ }

<!-- counter.vuka.html -->
<script lang="go">
package components
</script>

<button onClick={c.Inc}>{n}</button>

Right

<!-- counter.vuka.html -->
<script lang="go">
package components

type Counter struct {
	ui.Live
	n int
}

func (c *Counter) Inc() { c.n++ }
</script>

<button onClick={c.Inc}>{n}</button>