Issue #1764 — Trac XML-RPC transport: phpxmlrpc wire layer fataled on PHP 8

Symptom

The vendored third_party/phpxmlrpc/lib/xmlrpc.inc used the PHP 4 functions each() (removed in PHP 8.0) and split() (removed in PHP 7.0) at 15 sites. The first command the Trac XML-RPC interface sends — sendCmd() → xmlrpcmsg::createPayload() → xmlrpcval::serialize() — died:

PHP Fatal error: Uncaught Error: Call to undefined function each() in
  third_party/phpxmlrpc/lib/xmlrpc.inc:2946

so getIssue(), checkBugIDExistence(), addIssue() and buildViewBugLink() (the bug link rendered on execution screens) were all dead. connect() still reported success, because it only builds the client object and never touches a socket — which is why the failure was silent until a real command was sent.

Root cause

third_party/phpxmlrpc is the unmaintained TestLink 1.9.20 drop, written for PHP 4. #1635 fixed only the compile-time layer of the file; the runtime wire layer was never ported.

layer	site	conversion
header parse	2277	split("\r?\n", …) → preg_split('/\r?\n/', …)
full walks	2278, 2830, 3022, 3033, 3038, 3202, 3350	while(list($k,$v)=each($ar)) → foreach ($ar as $k => $v)
single pairs	2946, 2959, 3013, 3055, 3068, 3216	reset() + list($a,$b)=each() → guarded key()/current()
advancing pair	3004 + callers 3244/3253	structeach() re-implemented on key()/current()/next()
response length	2545	count($data) (TypeError on strings since PHP 8.0) → strlen($data)

structeach() was the only non-mechanical one: it returns the advancing pair, so it could not become a foreach. It was re-implemented with PHP's own each() algorithm — read the current pair, advance the pointer, return (0, 'value', 1, 'key'), false when exhausted — so its public contract is unchanged. Its two internal callers are full walks preceded by structreset(), so they became foreach.

Two fidelity traps found and handled: current() returns false on an empty array where each() yielded null (matters for scalarval() on a zero-arg xmlrpcval), and the slot order of the returned array is part of the observable contract.

Verification

• Behaviour-preservation proof — the pre-port library, with each()/split() reconstructed as a polyfill, was run against the patched file over 60+ observables (scalars, arrays, nested structs, every legacy accessor, the dump() helper, encode/decode of php objects, faults, datetimes). The diff of the serialized results is empty.
• Live round trip — ticket.get posted over TCP to a fixture endpoint: valid methodCall on the wire, set-cookie captured by parseResponseHeaders(), struct decoded.
• 31-case suite php tmp/verify_1764.php → 31 passed, 0 failed.

Not in scope

• xmlrpcs.inc (server side, 24 =& new) and xmlrpc_wrappers.inc (7) still fail php -l. TestLink never loads them, so the app is unaffected.
• tracxmlrpcInterface::connect() never probes the server — inherited 1.9.20 behaviour, and a product decision rather than part of this fix.
• No real Trac server exists in the CI environment, so the round trip is proven against a fixture speaking the same wire format, not against Trac's XmlRpcPlugin.