From 244282f855767755d0d3064658656d1e3d830226 Mon Sep 17 00:00:00 2001
From: marbocub <marbocub@gmail.com>
Date: Tue, 23 Dec 2025 02:18:00 +0900
Subject: [PATCH] Fix rotation expression errors in
 handleLegacyTangentPlaneOrientation() (#26058)

* Fix rotation expression handling

- Make added rotation angle unit the same as the original expression unit
- Keep rotated angle expressions within the accepted [-180, +180] range
---
 src/Mod/Part/App/AttachExtension.cpp | 41 +++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/src/Mod/Part/App/AttachExtension.cpp b/src/Mod/Part/App/AttachExtension.cpp
index cd812a61d3..f6b29b2ca4 100644
--- a/src/Mod/Part/App/AttachExtension.cpp
+++ b/src/Mod/Part/App/AttachExtension.cpp
@@ -607,6 +607,31 @@ void AttachExtension::handleLegacyTangentPlaneOrientation()
         }
 
         // convert placement and expressions according to the dominant axis
+        auto makeRotatedExpression =
+            [owner](const App::Expression* expr, double angle) -> App::Expression* {
+            if (!expr) {
+                return nullptr;
+            }
+
+            std::string unitSafeExprStr = "(" + expr->toString() + ")";
+            if (angle >= 0) {
+                unitSafeExprStr += " + " + std::to_string(angle);
+            }
+            else {
+                unitSafeExprStr += " - " + std::to_string(-angle);
+            }
+
+            if (const App::Expression* simple = expr->eval()) {
+                if (auto ue = dynamic_cast<const App::UnitExpression*>(simple)) {
+                    const auto& q = ue->getQuantity();
+                    if (q.getUnit() == Base::Unit::Angle) {
+                        unitSafeExprStr += " deg";
+                    }
+                }
+            }
+
+            return App::ExpressionParser::parse(owner, unitSafeExprStr.c_str());
+        };
         App::Expression* newExprX = nullptr;
         App::Expression* newExprY = nullptr;
         App::Expression* newExprYaw = nullptr;
@@ -625,8 +650,12 @@ void AttachExtension::handleLegacyTangentPlaneOrientation()
                 newExprX = App::ExpressionParser::parse(owner, expr.c_str());
             }
             if (exprYaw) {
-                std::string expr = "(" + exprYaw->toString() + ") + 90 deg";
-                newExprYaw = App::ExpressionParser::parse(owner, expr.c_str());
+                if (yaw > 90) {
+                    newExprYaw = makeRotatedExpression(exprYaw, -270);
+                }
+                else {
+                    newExprYaw = makeRotatedExpression(exprYaw, 90);
+                }
             }
         }
         else if (axis == 1) {  // normal mostly Y
@@ -644,8 +673,12 @@ void AttachExtension::handleLegacyTangentPlaneOrientation()
                 newExprX = App::ExpressionParser::parse(owner, exprY->toString().c_str());
             }
             if (exprYaw) {
-                std::string expr = "(" + exprYaw->toString() + ") - 90 deg";
-                newExprYaw = App::ExpressionParser::parse(owner, expr.c_str());
+                if (yaw < -90) {
+                    newExprYaw = makeRotatedExpression(exprYaw, 270);
+                }
+                else {
+                    newExprYaw = makeRotatedExpression(exprYaw, -90);
+                }
             }
         }
         else {