[SKETCH] Size the request-time base-variant fix (#106696)

[CybotTM]

Note

Sizing sketch only — NOT for merge, and not how TYPO3 Core is contributed (that goes through Gerrit). This exists to make the size of a correct request-time base-variant fix for forge #106696 tangible — the "big" alternative to the naive one-liner (CybotTM/typo3#1) and to the docs PR (TYPO3-Documentation/TYPO3CMS-Reference-CoreApi#6651).

Why the naive fix cannot work (recap)

Base variants are resolved in the request-less Site constructor, reached from the SiteResolver middleware before $GLOBALS['TYPO3_REQUEST'] is ever assigned (that happens only in the innermost frontend/Http/RequestHandler::handle()). So ip() silently returns false. A correct fix must make the base request-scoped at read time, which changes the lifecycle of Site and SiteLanguage.

What this branch implements

The new infrastructure a request-time fix needs:

• CurrentRequestHolder (new, ~50 LOC): a process-wide, request-scoped holder, external to Site (which is serialized into the runtime cache, so a live request must never live on it), with withRequest() save/restore for sub-requests.
• Services.yaml: registers it (public, shared).
• SiteResolver middleware: populates the holder with the request — which at that point already carries normalizedParams / the client IP — and restores it via try/finally.

These compile but intentionally do nothing on their own: the holder is populated and never read, because the large consuming surgery is not applied (it is the risky part being sized).

What a correct fix additionally needs (NOT in this branch — the sized surgery)

See SIZING.md for the file-by-file breakdown. In short: Site.php (stop eager resolve, lazy getBase(), ~100–150 LOC), SiteLanguage.php (lazy base, ~40–70 LOC), SiteMatcher canonical-base carve-out so identification stays request-independent while presentation becomes request-aware, backend SiteResolver + adminpanel preview holder population, and real FE-request functional tests (~200–320 LOC).

Size bands

Option	Files	LOC	Backport	Status
Naive fix (#1)	2	+45 / −1	—	broken (silent no-op)
Docs PR (#6651)	1–2	~30–80 prose	13.4 ✓	recommended
Correct fix (A+C hybrid)	~10–11	~450–700 (prod ~250–380, tests ~200–320)	main-only	this sketch sizes it
Reduced (site base only)	~5–6	~250	main-only	partial fix

≈ 10–15× the naive fix's LOC, main-only, with real BC / site-identity / cache-coherence risk across TypoLink, redirects, hreflang and CSP — for a capability the ecosystem already covers via a custom ExpressionLanguageProvider (b13/host-variants).

Verdict

NO-GO on a core code fix as the primary answer. Ship the docs PR (#6651), delegate request/host-dependent bases to the provider pattern, and only build this out if the maintainers explicitly mandate request-dependent base variants in core.

[CybotTM]

Alternative: explicit withRequest() variant → #3

Per @garvinhicking's review feedback (avoid the to-be-phased-out $GLOBALS['TYPO3_REQUEST']; treat Site as a value object), the v15, core-direction-aligned alternative lives in #3: no ambient state, an immutable Site::withRequest(): self clone, request flowing through the existing site request attribute.

Key finding from that buildout: the "purer" explicit approach is actually more invasive than this holder — replacing the site attribute with a clone breaks a core invariant (the attribute is object-identical to the SiteFinder result), so two identity comparisons (ShortcutAndMountPointRedirect, PageLinkBuilder) had to change to compare by identifier. The ambient holder here avoids that entirely.

#3 has since been hardened to core-mergeable shape (multi-reviewer pass): no SiteInterface BC break (getCanonicalBase()/withRequest() are concrete-only), __serialize() drops the bound request, Feature-106696 + Breaking-106696 changelog included, [FEATURE] commit. It is now 9 files (+ the two changelog entries) with the full suite green (SiteHandling 2510). Both variants confirm the mechanism is small; the architecture is the hard part. See #3 for the full comparison and honest limitations.