command/jsonchecks: Mark check result objects as experimental

This is a clumsy way to do this, but a pragmatic way to inform potential
consumers that this part of the format is not yet finalized without having
to read the docs to see our warning about that.

We need to get some practical experience with a few different consumers
making use of this format before we can be confident that it's designed
appropriately. We're not _expecting_ to break it, but we'd like to leave
the opportunity open in case we quickly learn that there's something
non-ideal about this design.

internal/command/jsonchecks/checks.go

@@ -70,6 +70,8 @@ func MarshalCheckStates(results *states.CheckResults) []byte {
 // object in the configuration even if Terraform Core encountered an error
 // before being able to determine the dynamic instances of the checkable object.
 type checkResultStatic struct {
+	ExperimentalNote experimentalNote `json:"//"`
+
 	// Address is the address of the checkable object this result relates to.
 	Address staticObjectAddr `json:"address"`
 
@@ -114,3 +116,9 @@ type checkProblem struct {
 	// intentionally an object to allow us to add other data over time, such
 	// as the source location where the failing condition was defined.
 }
+
+type experimentalNote struct{}
+
+func (n experimentalNote) MarshalJSON() ([]byte, error) {
+	return []byte(`"EXPERIMENTAL: see docs for details"`), nil
+}

internal/command/jsonchecks/checks_test.go

@@ -94,6 +94,7 @@ func TestMarshalCheckStates(t *testing.T) {
 			},
 			[]any{
 				map[string]any{
+					"//": "EXPERIMENTAL: see docs for details",
 					"address": map[string]any{
 						"kind":       "output_value",
 						"module":     "module.child",
@@ -117,6 +118,7 @@ func TestMarshalCheckStates(t *testing.T) {
 					"status": "fail",
 				},
 				map[string]any{
+					"//": "EXPERIMENTAL: see docs for details",
 					"address": map[string]any{
 						"kind":       "resource",
 						"mode":       "managed",
@@ -142,6 +144,7 @@ func TestMarshalCheckStates(t *testing.T) {
 					"status": "fail",
 				},
 				map[string]any{
+					"//": "EXPERIMENTAL: see docs for details",
 					"address": map[string]any{
 						"kind":       "output_value",
 						"name":       "a",
@@ -158,6 +161,7 @@ func TestMarshalCheckStates(t *testing.T) {
 					"status": "fail",
 				},
 				map[string]any{
+					"//": "EXPERIMENTAL: see docs for details",
 					"address": map[string]any{
 						"kind":       "resource",
 						"mode":       "managed",