We originally included this warning because the go-cty-yaml module wasn't
yet stable and it was also not extensively tested so it wasn't yet clear
if its behavior would need to change in some less common cases we hadn't
tested so far.
However, go-cty-yaml had its v1.0.0 release some time ago and is now
committed to preserving its current Marshal output unless it is found to
be non-compliant with the YAML 1.2 specification. This doc change means
that Terraform's yamlencode is now adopting a similar posture:
- The exact style details produced by the function for a particular input
are now frozen. It'll change only if we find that the function is
producing output that isn't valid per the YAML spec.
- If someone finds a YAML parser that cannot parse what yamlencode
produces but what it produces is valid per the YAML 1.2 spec, we'll
expect the parser to be corrected to better support the spec rather
than changing the yamlencode output.
There may be pragmatic exceptions if we encounter a situation we cannot
anticipate yet, but the above will be our general rule. This is really
just a specialization of the spirit of the v1.x Compatibility Promises,
tailored specifically to this function.
