Turn lanes reversed when reversing a way

[1ec5]

When reversing the direction of a roadway, the values within the turn:lanes, turn:lanes:forward, turn:lanes:backward, and turn:lanes:both_ways tags are incorrectly reversed.

Steps to reproduce:

1. Draw or select a way tagged highway=tertiary lanes=2 turn:lanes:forward=right.
2. Reverse the way’s direction.

Expected results:
highway=tertiary lanes=2 turn:lanes:backward=right

Actual results:
highway=tertiary lanes=2 turn:lanes:backward=left

It’s correct that forward became backward, but not that right became left. The left/right replacement behavior is intended to maintain consistency in tags that indicate a side of the road. However, the “left” and “right” in turn:* tags indicate maneuvers, not sides of the road. The backward direction before the reversal is the same as the forward direction after the reversal, so the tag shouldn’t start referring to a different connecting way.

This issue only reproduces with the values left and right, not with more complex turn:lanes values, such as left|right or slight_left, making this issue more surprising when it does occur. It’s especially subtle because turn lanes are only surfaced in the raw tag editor.