internal/cuedebug: turn openinline off by default

openinline makes evalv3 mimic evalv2's behavior in some ways in terms of
closedness, allowing some third party projects to continue working on
evalv3 even if they were relying on buggy closedness behavior on evalv2.

However, other projects and examples break because of openinline too,
which is especially puzzling for new users coming to CUE and trying
to use evalv3 for new projects while trying to follow the CUE spec.

Especially now that we have a new flat dynamic closedness mechanism,
closedness in evalv3 seems to behave much more like evalv2's
even with openinline=0, so the downside of disabling openinline by
default is greatly reduced.

Fixes #3688.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Ifc3d445196fd2eb36eca5f1a3accb9d91218a6ce
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1209503
Reviewed-by: Marcel van Lohuizen <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: mvdan

cmd/cue/cmd/testdata/script/issue3819.txtar

@@ -5,7 +5,6 @@ cmp stdout stdout.golden
 
 # -- evalv3 --
 env CUE_EXPERIMENT=evalv3=1
-env CUE_DEBUG=openinline=0
 exec cue eval -e output main.cue
 cmp stdout stdout.golden
 
@@ -57,4 +56,4 @@ level2: #Level2 & {
 structure: {
     f: "a"
 }
-settings: {}
+settings: {}

cmd/cue/cmd/testdata/script/vet_matchn.txtar

@@ -4,7 +4,6 @@ exec cue vet -c schema.cue data.json
 
 # With the new evaluator.
 env CUE_EXPERIMENT=evalv3=1
-env CUE_DEBUG=openinline=0
 exec cue vet -c schema.cue data.json
 
 -- data.json --
@@ -29,4 +28,4 @@ package githubactions
         "uses"?: string
         "run"?:  string
     })
-}
+}

internal/cuedebug/cuedebug.go

@@ -64,7 +64,7 @@ type Config struct {
 	//
 	// For the second issue, to open up the entire result of an inline struct,
 	// such an expression could be written as `openAll(expr).out`.
-	OpenInline bool `envflag:"default:true"`
+	OpenInline bool
 
 	// OpenDef disables the check for closedness of definitions.
 	OpenDef bool