If the string to be tested is an unknown value that's been refined with
a prefix and the prefix we're being asked to test is in turn a prefix of
that known prefix then we can return a known answer despite the inputs
not being fully known.
There are also some other similar deductions we can make about other
combinations of inputs.
This extra analysis could be useful in a custom condition check that
requires a string with a particular prefix, since it can allow the
condition to fail even on partially-unknown input, thereby giving earlier
feedback about a problem.
cty's new "refinements" concept allows us to reduce the range of unknown
values from our functions. This initial changeset focuses only on
declaring which functions are guaranteed to return a non-null result,
which is a helpful baseline refinement because it allows "== null" and
"!= null" tests to produce known results even when the given value is
otherwise unknown.
This commit also includes some updates to test results that are now
refined based on cty's own built-in refinement behaviors, just as a
result of us having updated cty in the previous commit.
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
