fix: preserve full source pricing on rate-locked rows

Restoring only price_list_rate on a mapped row dropped any manual discount or
margin, so re-running pricing produced a rate that differed from the source and
still failed the maintain-same-rate check on save.

Copy the source row's whole pricing block (rate, discount, margin) and skip
pricing rules for locked rows, in both get_item_details and the bulk
apply_price_list path.

erpnext/stock/get_item_details.py

@@ -133,18 +133,18 @@ def get_item_details(
 
 	source_row = get_rate_locked_source_row(ctx, doc)
 	if source_row:
-		out.price_list_rate = flt(source_row.get("price_list_rate")) or flt(source_row.get("rate"))
+		lock_source_rate(out, source_row)
 	else:
 		out.update(get_price_list_rate(ctx, item))
 
-	if (
-		not out.price_list_rate
-		and ctx.transaction_type == "selling"
-		and frappe.get_single_value("Selling Settings", "fallback_to_default_price_list")
-	):
-		fallback_args = ctx.copy()
-		fallback_args.price_list = frappe.get_single_value("Selling Settings", "selling_price_list")
-		out.update(get_price_list_rate(fallback_args, item))
+		if (
+			not out.price_list_rate
+			and ctx.transaction_type == "selling"
+			and frappe.get_single_value("Selling Settings", "fallback_to_default_price_list")
+		):
+			fallback_args = ctx.copy()
+			fallback_args.price_list = frappe.get_single_value("Selling Settings", "selling_price_list")
+			out.update(get_price_list_rate(fallback_args, item))
 
 	ctx.customer = current_customer
 
@@ -159,9 +159,8 @@ def get_item_details(
 		if ctx.get(key) is None:
 			ctx[key] = value
 
-	data = get_pricing_rule_for_item(ctx, doc=doc, for_validate=for_validate)
-
-	out.update(data)
+	if not source_row:
+		out.update(get_pricing_rule_for_item(ctx, doc=doc, for_validate=for_validate))
 
 	if (
 		frappe.get_single_value("Stock Settings", "auto_create_serial_and_batch_bundle_for_outward")
@@ -234,6 +233,19 @@ def maintain_same_rate_enabled(ctx: ItemDetailsCtx) -> bool:
 	return bool(cint(frappe.get_cached_value("Selling Settings", "None", "maintain_same_sales_rate")))
 
 
+def lock_source_rate(out: frappe._dict, source_row) -> None:
+	"""Copy the source row's whole pricing block onto out so a mapped row keeps its
+	exact rate. Pricing rules are skipped for these rows, so nothing re-derives it and
+	the manual discount or margin that made rate differ from price_list_rate survives.
+	"""
+	out.price_list_rate = flt(source_row.get("price_list_rate")) or flt(source_row.get("rate"))
+	out.rate = flt(source_row.get("rate"))
+	out.discount_percentage = flt(source_row.get("discount_percentage"))
+	out.discount_amount = flt(source_row.get("discount_amount"))
+	out.margin_type = source_row.get("margin_type")
+	out.margin_rate_or_amount = flt(source_row.get("margin_rate_or_amount"))
+
+
 def set_valuation_rate(out: frappe._dict, ctx: frappe._dict):
 	from erpnext.selling.doctype.product_bundle.product_bundle import get_active_product_bundle
 
@@ -1700,9 +1712,8 @@ def apply_price_list_on_item(ctx, doc=None):
 
 	source_row = get_rate_locked_source_row(ctx, doc)
 	if source_row:
-		item_details = frappe._dict(
-			price_list_rate=flt(source_row.get("price_list_rate")) or flt(source_row.get("rate"))
-		)
+		item_details = frappe._dict()
+		lock_source_rate(item_details, source_row)
 	else:
 		item_details = get_price_list_rate(ctx, item_doc)
 
@@ -1711,7 +1722,8 @@ def apply_price_list_on_item(ctx, doc=None):
 	)
 	ctx.stock_qty = flt(ctx.qty) * flt(ctx.conversion_factor)
 
-	item_details.update(get_pricing_rule_for_item(ctx, doc=doc))
+	if not source_row:
+		item_details.update(get_pricing_rule_for_item(ctx, doc=doc))
 
 	return item_details
 

erpnext/stock/tests/test_get_item_details.py

@@ -259,3 +259,65 @@ class TestGetItemDetail(ERPNextTestSuite):
 		finally:
 			frappe.db.set_single_value("Buying Settings", "maintain_same_rate", original)
 			frappe.clear_cache(doctype="Buying Settings")
+
+	def test_maintain_same_rate_keeps_source_discount_on_refetch(self):
+		"""A mapped row with a manual discount has rate != price_list_rate. Re-fetch must
+		keep the source's rate and discount, not just the pre-discount price, or the
+		recomputed rate diverges from the reference and fails maintain-same-rate on save.
+		"""
+		from frappe.utils import flt
+
+		from erpnext.buying.doctype.purchase_order.test_purchase_order import create_purchase_order
+
+		item_code = "_Test Item"
+		price_list = "_Test Buying Price List"
+
+		original = frappe.db.get_single_value("Buying Settings", "maintain_same_rate")
+		frappe.db.set_single_value("Buying Settings", "maintain_same_rate", 1)
+		frappe.clear_cache(doctype="Buying Settings")
+
+		try:
+			po = create_purchase_order(item_code=item_code, rate=90, qty=1)
+
+			row_name = "pr-row-1"
+			# price_list_rate 100 with a 10% discount gives the effective rate 90.
+			pr_doc = {
+				"doctype": "Purchase Receipt",
+				"items": [
+					{
+						"name": row_name,
+						"item_code": item_code,
+						"purchase_order_item": po.items[0].name,
+						"price_list_rate": 100,
+						"rate": 90,
+						"discount_percentage": 10,
+					}
+				],
+			}
+			ctx = frappe._dict(
+				item_code=item_code,
+				doctype="Purchase Receipt",
+				company=po.company,
+				supplier=po.supplier,
+				currency=po.currency,
+				conversion_rate=1.0,
+				price_list=price_list,
+				price_list_currency=po.currency,
+				plc_conversion_rate=1.0,
+				warehouse="_Test Warehouse - _TC",
+				uom=po.items[0].uom,
+				stock_uom=po.items[0].stock_uom,
+				qty=1,
+				child_docname=row_name,
+				is_return=0,
+				is_internal_supplier=0,
+				ignore_pricing_rule=1,
+			)
+
+			out = get_item_details(ctx, pr_doc)
+			self.assertEqual(flt(out.get("price_list_rate")), 100)
+			self.assertEqual(flt(out.get("rate")), 90)
+			self.assertEqual(flt(out.get("discount_percentage")), 10)
+		finally:
+			frappe.db.set_single_value("Buying Settings", "maintain_same_rate", original)
+			frappe.clear_cache(doctype="Buying Settings")