fix: allow trial for returning customers whose cancelled WCS sub had zero renewals

[superdav42]

Summary

• Fixes ~14% of UM+WCS checkouts where _schedule_trial_end=0 and _schedule_next_payment is set to now+billing_period instead of now+trial_period, causing the first charge to fire immediately instead of after the advertised trial.
• Real reported case: Sub #61444 (KURSO PRO, $99/mo, 15-day trial) — customer used 14 days and would never have been billed.

Root cause

has_trial() in inc/checkout/class-cart.php blocked trial eligibility for any customer with a cancelled WCS subscription whose parent WC order was completed — even when that subscription was cancelled due to a double-checkout or payment-gateway race and the customer never completed a billing cycle.

Failure chain

1. Customer submits checkout form twice (double-click, page refresh, etc.)
2. Two WCS subscriptions are created; UM/WCS cancels the first — parent WC order is completed
3. Next valid checkout: has_trial() finds the cancelled sub → return false
4. maybe_create_product gets $days_to_start = 0 → no _subscription_trial_length on WC product
5. WCS creates subscription with _schedule_trial_end = 0 and next_payment = now+billing_period
6. Customer is charged after one month instead of after the trial

The existing guard (added in 2.4.14) already skips cancelled subs whose parent order was not completed. This PR adds a second gate: also skip if the subscription had zero renewal orders, meaning it never completed a billing cycle.

Change

File: inc/checkout/class-cart.php — has_trial(), line ~2310

// After the existing parent-order guard:
if (method_exists($subscription, 'get_related_orders')) {
    $renewal_ids = $subscription->get_related_orders('ids', 'renewal');
    if (empty($renewal_ids)) {
        continue; // No renewals = never completed a billing cycle — allow trial.
    }
}

Verification

Reproduced and fixed in the dev WordPress environment:

Scenario	Before	After
Cancelled sub, completed parent, 0 renewals (error path)	has_trial() = false ❌	has_trial() = true ✅
Cancelled sub, completed parent, 1+ renewals (genuine returner)	has_trial() = false ✅	has_trial() = false ✅
Active / on-hold sub	has_trial() = false ✅	has_trial() = false ✅
Cancelled sub, incomplete parent (declined card)	has_trial() = true ✅	has_trial() = true ✅

Verified by running the exact subscription/cart logic directly in wp eval against a real cancelled+completed sub with 0 renewals (sub #73 in dev).

Impact

• Fix is backward-compatible. No schema changes, no migrations.
• Genuine returning customers (who completed at least one renewal payment) are still correctly blocked from getting another trial.
• Customers whose checkout errored (double-checkout, race condition) are no longer penalised with lost trials.
• The kp-trial-cancel-guard.php mu-plugin on Kursopro guards a related but distinct symptom — can be audited for removal once this and the sync_subscription_status guards (2.2.x) are confirmed stable in production.

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Summary by CodeRabbit

Release Notes

• Bug Fixes
  • Enhanced trial eligibility evaluation for customers with cancelled subscriptions. Users may now qualify for trials when their cancelled subscription's parent order is completed or in certain statuses, improving trial access.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: dac6d167-efee-41f6-9c95-a95f97dc8ace

📥 Commits

Reviewing files that changed from the base of the PR and between 695aa2c and 5ed6b1a.

📒 Files selected for processing (1)

• inc/checkout/class-cart.php

---

📝 Walkthrough

Walkthrough

The has_trial() method in the cart class now applies refined logic for cancelled subscriptions. When a cancelled subscription's parent order has a completed, processing, or refunded status, the method checks for related renewal orders to determine trial eligibility rather than automatically blocking it.

Changes

Cohort / File(s)	Summary
Trial Eligibility Logic inc/checkout/class-cart.php	Modified has_trial() to conditionally inspect renewal orders when handling cancelled subscriptions with completed/processing/refunded parent orders. Trial is blocked only when renewal orders exist; allowed when renewal IDs are empty.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• fix: 11 checkout/trial/site-creation bugs from KursoPro production #372: Modifies trial-eligibility logic in the same file by adjusting how cancelled subscriptions and renewal orders affect has_trial() behavior.

Poem

🐰 A rabbit hops through cancelled tales,
Where trials bloom when renewal fails,
With renewed grace, the logic flows,
Eligibility where order-state grows! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly describes the main fix: allowing trial eligibility for returning customers whose cancelled WCS subscriptions had zero renewals.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch bugfix/wcs-trial-eligibility-returning-customers

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Performance Test Results

Performance test results for 0e929b4 are in 🛎️!

Note: the numbers in parentheses show the difference to the previous (baseline) test run. Differences below 2% or 0.5 in absolute values are not shown.

URL: /

Run	DB Queries	Memory	Before Template	Template	WP Total	LCP	TTFB	LCP - TTFB
0	41 (-5 / -12% )	37.80 MB	811.50 ms (-87.00 ms / -11% )	167.50 ms (+15.50 ms / +9% )	1040.00 ms (-64.50 ms / -6% )	1960.00 ms (-154.00 ms / -8% )	1865.75 ms (-169.20 ms / -9% )	88.40 ms (-1.85 ms / -2% )
1	56	49.10 MB	944.00 ms	139.50 ms (-3.50 ms / -3% )	1086.50 ms	2068.00 ms	1990.05 ms	80.70 ms