This includes a fix to prevent unintentional infinite recursion when
trying to unify multiple object types to a single type for conversion to
list(any).
Sadly I wasn't able to reproduce the problem as reported (in #20728), so
therefore I wasn't able to write a Terraform test for it, but I have
confirmed that the cty behavior here was incorrect anyway (recursively
calling the same function we're already in with the same arguments is
clearly not productive) and so this change will allow whatever situation
that was to terminate with a type conversion error, rather than causing a
stack overflow.
It's likely that there is another bug lurking under this, since the
problematic code here was supposed to be unreachable, but avoiding the
crash is the priority for now. If the problem re-surfaces then it should
at least be an error message with some additional context about what the
goal of the caller was.
This also includes an unrelated fix for the gocty package, which doesn't
affect Terraform because it makes very little use of that package.
This includes:
- An additional check in the format stdlib function to fail if there are
too many arguments given, rather than silently ignoring.
- Refinements for the type unification behavior to allow unification of
object/tuple types into weaker map/list types when no other unification
is possible.
- Improvements to the error messages for failed type conversions on
collection and structural types to talk about mismatching element types
where possible, rather than the outer value.
Martin Atkins