fix(framework): await pending language change in connectedCallback instead of skipping first render

[ilhan007]

Summary

Follow-up to #13602. That PR made connectedCallback bail out early for language-aware components mounted while a language change was in progress. The early-return path silently skipped onEnterDOM(), _fullyConnected = true, and the _domRefReadyPromise resolution — so consumers that register listeners or observers in onEnterDOM never saw those side effects wired up.

Reporter symptom

Reported against udex-footer (built on top of UI5 Web Components):

onEnterDOM(): void {
    if (isDesktop()) {
        this.setAttribute("desktop", "");
    }
    ResizeHandler.register(this, this._handleResizeBound);
}

• App calls setLanguage("zh_CN") without awaiting → language change pending.
• <udex-footer> inserted while pending → connectedCallback hits the early return at UI5Element.ts:362.
• ResizeHandler.register never runs → mobile Accordion never appears because the resize observer never fires.

Fix

Instead of bailing out (which desynchronized the lifecycle), await the pending language change and then continue on the normal render path. To make that ergonomic, languageChangePending in Language.ts is repurposed from a boolean flag into a promise handle — the in-flight settlement promise, or null when no change is pending.

Language.ts

• languageChangePending: Promise<void> | null replaces the boolean.
• A single startLanguageChange helper builds the promise (chaining fireLanguageChange + the deferred reRenderAllUI5Elements) and clears the field on .finally — only if a newer change hasn't already replaced it.
• Both setLanguage() and the cross-runtime attachConfigChange handler share the helper, so both paths keep the field consistent.
• getLanguageChangePending() now returns the in-flight promise or null.

UI5Element.ts — connectedCallback

const languageChangePending = getLanguageChangePending();
if (ctor.getMetadata().isLanguageAware() && languageChangePending) {
    await languageChangePending;
}
// ...normal render path continues, onEnterDOM fires exactly as usual

A small guard skips the redundant renderImmediately(this) if the deferred reRenderAllUI5Elements already rendered the element during the await.

UI5Element.ts — _invalidate
Unchanged. getLanguageChangePending() in a truthy context still means "a change is in flight, don't invalidate now".

Why this shape

• Preserves the lifecycle invariant. onEnterDOM fires exactly once, after the first render, on the natural code path — no deferred bookkeeping.
• Single source of truth. One field on Language.ts — either a promise or null — captures pending-ness. No boolean/promise pair to keep in sync.
• Composable. Any future consumer that needs "wait for locale data to be ready" can await getLanguageChangePending() without adding another synchronization surface.

Tests

• New test element packages/base/test/test-elements/LanguageAwareLifecycle.tsx — languageAware: true, counts each lifecycle hook invocation.
• New spec packages/base/cypress/specs/LanguageAwareLifecycle.cy.tsx:
  • onEnterDOM fires exactly once after a pending language change resolves
  • onEnterDOM does not fire a second time on a subsequent re-render
  • onEnterDOM does not fire if the element is removed before rendering

Verified locally:

• New tests: 3/3 pass with the fix, 2/3 fail without the fix (confirms the regression is caught).
• Existing main/cypress/specs/DatePicker_cldr_race.cy.tsx (from fix(framework): prevent language-aware components from rendering before CLDR data loads #13602): still passes.
• Existing base/cypress/specs/i18n_texts.cy.tsx: still passes.
• yarn lint clean.

Backport

Should be cherry-picked to the 2.23.x line since #13602 shipped there and Udex is affected.

Related

• fix(framework): prevent language-aware components from rendering before CLDR data loads #13602 introduced the early return.
• Reported by the UDEX (Digital Design System) team — sapudex/digital-design-system Footer component.

[sap-ui5-webcomponents-release]

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[sap-ui5-webcomponents-release]

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