I have these profiled rectangle.
I need to Bend it around Z-axis (Face #2 need to go to right) thus angle between faces #1 and #2 be exactly 45 degress.
This is rather easy to do.
Just add a Simple Deform Modifier.
Set it to Bend and select the right axis.
Enter the desired angle (it's 45° by default)
In this case bending along the Z axis doesn't work as expected.
To make it work, rotate the object's origin by -90°, or use an empty rotated by -90°.
Thanks to @lemon, @plem and @robin-betts for pointing that out.