Bugfix — Issue #1749: testcase::deletePlatformsByLink() — foreach() on null for an unknown link id

Problem

testcase::deletePlatformsByLink() raised E_WARNING foreach() argument must be of type array|object, null given whenever the supplied tcplat_link_id matched no testcase_platforms row — a stale chip (already unassigned in another tab) or a concurrent unassign. The request still answered normally; the only symptom was one Error row pushed into the Event Viewer (events, log_level=2) pointing at lib/functions/testcase.class.php.

Reproduce at HEAD (fresh-import CI box, no projects exist — build the fixture first):

php tmp/fixtures_1749.php      # tproject prefix PL1749, 1 TC + version, 1 platform, 1 link
php tmp/repro_1749.php

→ pre-fix: FAIL caseA stale-link-id warnings=1 at testcase.class.php - Line 9890; post-fix: warnings=0.

Root Cause

1. database::get_recordset() (lib/functions/database.class.php:787) starts with $output = null and only appends rows inside while($row = $this->fetch_array($result)). For an empty result set the loop body never runs, so the method returns null (line 799).
2. deletePlatformsByLink() (lib/functions/testcase.class.php:9888) assigns that result to $rs and then runs foreach($rs as $link) (line 9890) with no guard → PHP 8 raises the warning.
3. set_error_handler("watchPHPErrors") (lib/functions/logger.class.php:1483) persists the warning as one events row.

PHP 7 tolerated foreach(null) silently; PHP 8 promoted it to a warning, so the defect was latent until the 2.0.1 PHP 8 target.

Blast radius:

• lib/testcases/testcaseCommands.class.php:1584 — legacy test-spec platform unassign (tcEdit doAction=removePlatform), no ownership pre-check → fully exposed.
• api/testcases/index.php:3096 — modern BFF remove_platform. Its own SELECT guard at :3084-3095 already 404s a stale id, so it is safe today, but the guard is not atomic: a concurrent unassign between the SELECT and the DELETE re-opens the window.
• Sibling deletePlatforms() (:9899) is already null-safe ((array) cast at :9922) and was left untouched.

Fix

lib/functions/testcase.class.php — guard the iteration; an empty/unknown link id becomes a clean no-op:

$rs = $this->db->get_recordset($sql);

// get_recordset() returns null for an empty result set (database.class.php:787);
// an unknown/stale link id must be a clean no-op, not an E_WARNING (#1749).
foreach((array)$rs as $link) {
  $this->deletePlatforms($safeTCID, $link['tcversion_id'],
    $link['platform_id'],$audit);
}

The (array) cast is the same pattern already used in this method (:9878) and in deletePlatforms() (:9922). Rejected alternatives: a local is_array() check (noisier, inconsistent with the file) and changing get_recordset() globally (blast radius far beyond this bug). No user-facing strings → no locale-bundle additions.

Files Changed

• lib/functions/testcase.class.php — deletePlatformsByLink(): (array) cast on the record set.
• tmp/fixtures_1749.php — fixture (project + TC + platform + link).
• tmp/repro_1749.php — CLI repro/regression harness (stale id + positive control).
• tmp/TLU_Test_Cases.md — suite "Regression — Issue #1749", 7/7 PASS.

Verification

All checks on the fresh-import CI box:

• Pre-fix tmp/repro_1749.php = 1 E_WARNING at testcase.class.php:9890; post-fix = 0, and the positive control (real link) still deletes the row.
• HTTP POST api/testcases/index.php?action=remove_platform with a stale tcplat_link_id → HTTP 404 clean JSON error, 0 new events rows.
• Same action with the valid link id → HTTP 200, row removed, free list updated.
• php -l lib/functions/testcase.class.php clean.

Address: Fixes #1749 (pushed on the fix branch; CI lands it on the default branch).