# Objective
Related to #12981
Presently, there is a footgun where we allow non-normalized vectors to
be passed in the `axis` parameters of `Transform::rotate_axis` and
`Transform::rotate_local_axis`. These methods invoke
`Quat::from_axis_angle` which expects the vector to be normalized. This
PR aims to address this.
## Solution
Require `Dir3`-valued `axis` parameters for these functions so that the
vector's normalization can be enforced at type-level.
---
## Migration Guide
All calls to `Transform::rotate_axis` and `Transform::rotate_local_axis`
will need to be updated to use a `Dir3` for the `axis` parameter rather
than a `Vec3`. For a general input, this means calling `Dir3::new` and
handling the `Result`, but if the previous vector is already known to be
normalized, `Dir3::new_unchecked` can be called instead. Note that
literals like `Vec3::X` also have corresponding `Dir3` literals; e.g.
`Dir3::X`, `Dir3::NEG_Y` and so on.
---
## Discussion
This axis input is unambigiously a direction instead of a vector, and
that should probably be reflected and enforced by the function
signature. In previous cases where we used, e.g., `impl TryInto<Dir3>`,
the associated methods already implemented (and required!) additional
fall-back logic, since the input is conceptually more complicated than
merely specifying an axis. In this case, I think it's fairly
cut-and-dry, and I'm pretty sure these methods just predate our
direction types.
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