From 0ba52f0e2294dda0ba2e46f5ab3267e019aae076 Mon Sep 17 00:00:00 2001
From: Benjamin Nauck <benjamin@nauck.se>
Date: Tue, 11 Feb 2025 15:33:30 +0100
Subject: [PATCH] Make modulo require units to be same or dimensionless

Fixes #19517
---
 src/App/Expression.cpp                 |  4 +++-
 src/Mod/Spreadsheet/TestSpreadsheet.py | 14 +++++++++-----
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/App/Expression.cpp b/src/App/Expression.cpp
index 596930a0bc..f2314627f5 100644
--- a/src/App/Expression.cpp
+++ b/src/App/Expression.cpp
@@ -2471,7 +2471,9 @@ Py::Object FunctionExpression::evaluate(const Expression *expr, int f, const std
     case MOD:
         if (e2.isNone())
             _EXPR_THROW("Invalid second argument.",expr);
-        unit = v1.getUnit() / v2.getUnit();
+        if (v1.getUnit() != v2.getUnit() && !v1.isDimensionless() && !v2.isDimensionless())
+            _EXPR_THROW("Units must be equal or dimensionless.",expr);
+        unit = v1.getUnit();
         break;
     case POW: {
         if (e2.isNone())
diff --git a/src/Mod/Spreadsheet/TestSpreadsheet.py b/src/Mod/Spreadsheet/TestSpreadsheet.py
index d51719adf8..a5d78a9810 100644
--- a/src/Mod/Spreadsheet/TestSpreadsheet.py
+++ b/src/Mod/Spreadsheet/TestSpreadsheet.py
@@ -1088,14 +1088,18 @@ class SpreadsheetCases(unittest.TestCase):
         self.assertEqual(sheet.B8, rot)
         self.assertEqual(sheet.C8, pla)
 
-    def testIssue3128(self):
-        """Regression test for issue 3128; mod should work with arbitrary units for both arguments"""
+    def testIssue19517(self):
+        """Regression test for issue 19517; mod should work with units"""
         sheet = self.doc.addObject("Spreadsheet::Sheet", "Spreadsheet")
         sheet.set("A1", "=mod(7mm;3mm)")
-        sheet.set("A2", "=mod(7kg;3mm)")
         self.doc.recompute()
-        self.assertEqual(sheet.A1, Units.Quantity("1"))
-        self.assertEqual(sheet.A2, Units.Quantity("1 kg/mm"))
+        self.assertEqual(sheet.A1, Units.Quantity("1 mm"))
+        try:
+            sheet.set("A2", "=mod(7kg;3mm)")
+            self.doc.recompute()
+            self.fail("Units need to be the same or dimensionless")
+        except Exception:
+            pass
 
     def testIssue3363(self):
         """Regression test for issue 3363; Nested conditionals statement fails with additional conditional statement in false-branch"""