Invalid regexp warning in Project Element Type edition form

When editing an element type in a project in the frontend, you get this warning

Unable to check <input pattern='[-a-zA-Z0-9_]+'> because the pattern is not a valid regexp: invalid character in class in regular expression

which does not come from the computed I'm an idiot sandwich, but from the HTML obviously

        <input
          class="input"
          type="text"
          pattern="[-a-zA-Z0-9_]+"
          :disabled="loading || null"
          required
          v-model="fields.slug"
        />

in the console. The fix is to escape the -, MR incoming.