Incorrect Due Date validation due to type mismatch in workflow submission (version-15)

[Dev1-digitalistech]

Information about bug

In ERPNext version-15, there is a bug in due date validation inside:

erpnext/accounts/party.py

Function:
validate_due_date_with_template()

The issue occurs due to inconsistent data types between posting_date and default_due_date, especially when a document is submitted via Workflow.

Steps to Reproduce

1. Enable a Workflow on Purchase Invoice
2. Create a Purchase Invoice from UI
3. Set:
   • Posting Date = 2026-04-23
   • Bill Date = 2026-04-22
   • Due Date = 2026-04-23 (same as expected default)
4. Submit using Workflow action (e.g., Approve)

Actual Behavior

Validation incorrectly triggers:

"default_due_date != posting_date"

Even when both dates are logically the same.

Expected Behavior

Validation should not trigger when posting_date and default_due_date are equal.

Module

accounts

Version

Frappe Framework: v15.102.1 (HEAD)
ERPNext: v15.101.0 (HEAD)

Installation method

FrappeCloud

Relevant log output / Stack trace / Full Error Message.

🔍 Root Cause
Type mismatch during comparison:

default_due_date = '2026-04-23'  (string)
posting_date = datetime.date(2026, 4, 23)  (date object)

Comparison:
'2026-04-23' != datetime.date(2026, 4, 23) → True (incorrect logically)

This happens specifically in workflow submission because:
- frappe.get_doc + load_from_db() converts fields into Python date objects
- while get_due_date_from_template() returns string
💡 Suggested Fix
Normalize all date values using getdate() before comparison.

Example fix:

default_due_date = getdate(get_due_date_from_template(template_name, posting_date, bill_date))
posting_date = getdate(posting_date)
due_date = getdate(due_date)

if default_due_date != posting_date and due_date > default_due_date:
    ...




📌 Additional Context
This issue only appears in workflow-based submission.
Normal save/submit flow may not trigger this due to different data handling.