terraform/internal/experiments/testing.go

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experiments: a mechanism for opt-in experimental language features Traditionally we've preferred to release new language features in major releases only, because we can then use the beta cycle to gather feedback on the feature and learn about any usability challenges or other situations we didn't consider during our design in time to make those changes before inclusion in a stable release. This "experiments" feature is intended to decouple the feedback cycle for new features from the major release rhythm, and thus allow us to release new features in minor releases by first releasing them as experimental for a minor release or two, adjust for any feedback gathered during that period, and then finally remove the experiment gate and enable the feature for everyone. The intended model here is that anything behind an experiment gate is subject to breaking changes even in patch releases, and so any module using these experimental features will be broken by a future Terraform upgrade. The behavior implemented here is: - Recognize a new "experiments" setting in the "terraform" block which allows module authors to explicitly opt in to experimental features. terraform { experiments = [resource_for_each] } - Generate a warning whenever loading a module that has experiments enabled, to avoid accidentally depending on experimental features and thus risking unexpected breakage on next Terraform upgrade. - We check the enabled experiments against the configuration at module load time, which means that experiments are scoped to a particular module. Enabling an experiment in one module does not automatically enable it in any other module. This experiments mechanism is itself an experiment, and so I'd like to use the resource for_each feature to trial it. Because any configuration using experiments is subject to breaking changes, we are free to adjust this experiments feature in future releases as we see fit, but once for_each is shipped without an experiment gate we'll be blocked from making significant changes to it until the next major release at least.
2019-07-10 21:37:11 +02:00
package experiments
import (
"testing"
)
// OverrideForTesting temporarily overrides the global tables
// of experiments in order to allow for a predictable set when unit testing
// the experiments infrastructure code.
//
// The correct way to use this function is to defer a call to its result so
// that the original tables can be restored at the conclusion of the calling
// test:
//
// defer experiments.OverrideForTesting(t, current, concluded)()
//
// This function modifies global variables that are normally fixed throughout
// our execution, so this function must not be called from non-test code and
// any test using it cannot safely run concurrently with other tests.
func OverrideForTesting(t *testing.T, current Set, concluded map[Experiment]string) func() {
// We're not currently using the given *testing.T in here, but we're
// requiring it anyway in case we might need it in future, and because
// it hopefully reinforces that only test code should be calling this.
realCurrents := currentExperiments
realConcludeds := concludedExperiments
currentExperiments = current
concludedExperiments = concluded
return func() {
currentExperiments = realCurrents
concludedExperiments = realConcludeds
}
}