fix: warning message for new item standard cost (#56885)

erpnext/stock/doctype/item_standard_cost/item_standard_cost.js

@@ -13,4 +13,33 @@ frappe.ui.form.on("Item Standard Cost", {
 			};
 		});
 	},
+
+	refresh(frm) {
+		frm.trigger("show_backdated_block_warning");
+	},
+
+	item_code(frm) {
+		frm.trigger("show_backdated_block_warning");
+	},
+
+	effective_date(frm) {
+		frm.trigger("show_backdated_block_warning");
+	},
+
+	show_backdated_block_warning(frm) {
+		if (frm.doc.docstatus !== 0 || !frm.doc.item_code || !frm.doc.effective_date) {
+			frm.set_intro("");
+			return;
+		}
+		frm.set_intro(
+			__(
+				"On submission, stock transactions for Item {0} cannot be posted with a date before {1} — backdated entries will be blocked.",
+				[
+					frappe.utils.escape_html(frm.doc.item_code).bold(),
+					frappe.datetime.str_to_user(frm.doc.effective_date).bold(),
+				]
+			),
+			"yellow"
+		);
+	},
 });

erpnext/stock/doctype/item_standard_cost/item_standard_cost.py

@@ -33,6 +33,25 @@ class ItemStandardCost(Document):
 		self.validate_item()
 		self.validate_effective_date()
 		self.validate_rate()
+		self.warn_backdated_transactions_will_be_blocked()
+
+	def warn_backdated_transactions_will_be_blocked(self):
+		# Heads-up while creating (R2 enforces it later on every stock voucher): once this rate is
+		# effective, the item's stock transactions cannot be dated before the effective date.
+		if not self.is_new():
+			return
+		frappe.msgprint(
+			_(
+				"Once this Standard Cost is submitted, stock transactions for Item {0} in {1} cannot be posted with a date before the Effective Date {2}. Post any backdated entries before submitting."
+			).format(
+				get_link_to_form("Item", self.item_code),
+				frappe.bold(self.company),
+				frappe.bold(frappe.format(self.effective_date, "Date")),
+			),
+			title=_("Backdated Entries Will Be Blocked"),
+			indicator="orange",
+			alert=True,
+		)
 
 	def validate_item(self):
 		if not frappe.get_cached_value("Item", self.item_code, "is_stock_item"):