internal/cueexperiment: mark YAMLV3Decoder as deprecated too

Just like the modules experiment, thanks to the recent patch by Roger.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Id9c2d0e7c28c23169fc040644930e4692fffb3ba
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1200596
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mvdan

internal/cueexperiment/exp.go

@@ -19,7 +19,7 @@ var Flags struct {
 	// with CUE_EXPERIMENT=yamlv3decoder=1 who must still suppport older CUE versions,
 	// but currently the feature is always enabled.
 	// TODO(mvdan): remove for v0.12.
-	YAMLV3Decoder bool `envflag:"default:true"`
+	YAMLV3Decoder bool `envflag:"deprecated,default:true"`
 
 	// EvalV3 enables the new evaluator. The new evaluator addresses various
 	// performance concerns.

internal/cueexperiment/exp_test.go

@@ -23,12 +23,10 @@ func TestInit(t *testing.T) {
 	qt.Assert(t, qt.IsTrue(Flags.Modules))
 	qt.Assert(t, qt.IsTrue(Flags.YAMLV3Decoder))
 
-	// Check that we can disable the YAML v3 experiment.
+	// Check that we cannot disable the YAML v3 experiment.
 	t.Setenv("CUE_EXPERIMENT", "yamlv3decoder=0")
 	err = initAlways()
-	qt.Assert(t, qt.IsNil(err))
-	qt.Assert(t, qt.IsTrue(Flags.Modules))
-	qt.Assert(t, qt.IsFalse(Flags.YAMLV3Decoder))
+	qt.Assert(t, qt.ErrorMatches(err, `cannot parse CUE_EXPERIMENT: cannot change default value of deprecated flag "yamlv3decoder"`))
 
 	// Check that we cannot disable the modules experiment.
 	t.Setenv("CUE_EXPERIMENT", "modules=0")