tftypes: Disallow msgpack unmarshalling to call NewValue(DynamicPseudoType, nil)

[bflad]

terraform-plugin-go version

main branch after #94 is reviewed/merged, but should be handled before next release

Relevant Code

terraform-plugin-go/tftypes/value_msgpack.go

Lines 321 to 326 in 7943864

	switch {
	case length == -1:
	return NewValue(DynamicPseudoType, nil), nil
	case length != 2:
	return Value{}, path.NewErrorf("expected %d elements in DynamicPseudoType array, got %d", 2, length)
	}

Expected Behavior

Code should return error instead of calling NewValue() in manner that will panic.

Actual Behavior

If condition is hit after #94 is merged, code will panic.

Steps to Reproduce

Needs unit test added.

References

• tftypes: Enhance Type Comparisons Functionality #94

[paddycarver]

We should, at the very least, be using newValue instead of NewValue, so we can handle the error instead of panicking.

[github-actions]

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