internal/cueexperiment: enable embed experiment by default

As Paul announced in the embed proposal discussion on GitHub [1],
we have moved the proposal to a "likely accept" stage
and we are enabling the feature by defalut for CUE v0.12.

Enable it by default for the first alpha, v0.12.0-alpha.1,
for the sake of giving it as much testing as possible before v0.12.0.

While here, update the TODOs in the symlink embedding testscript file.
We ended up deciding to support symlinks, but the test wasn't updated.

[1]: https://cuelang.org/discussion/3264

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I499940a2dc799552963783174ed30dc0a312d925
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1205861
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Paul Jolly <paul@myitcv.io>

cmd/cue/cmd/help.go

@@ -254,8 +254,8 @@ and use APIs like yaml.Extract to decode as a list.
 
 Note that embedding cue files is not supported at this time.
 
-Note: support for embed is experimental, and is enabled via
-CUE_EXPERIMENT=embed.
+Note: support for embed is experimental, and can be disabled via
+CUE_EXPERIMENT=embed=0.
 
 For more details and discussion, see the proposal linked from
 https://cuelang.org/discussion/3264.

cmd/cue/cmd/testdata/script/embed.txtar

@@ -1,7 +1,8 @@
+# Embedding is enabled by default, but it can still be disabled.
+env CUE_EXPERIMENT=embed=0
 ! exec cue eval
 cmp stderr out/noembed
-
-env CUE_EXPERIMENT=embed
+env CUE_EXPERIMENT=
 
 exec cue eval
 cmp stdout out/eval

cmd/cue/cmd/testdata/script/embed_err.txtar

@@ -1,12 +1,9 @@
-env CUE_EXPERIMENT=embed
-
 ! exec cue eval
 ! stdout .
 cmp stderr out/err
 
-# On systems with symlink support, check that we don't allow embedding symlinks.
-# TODO(mvdan): we don't reject valid symlinks yet; see https://cuelang.org/issue/3299.
-# TODO: if we support symlinks in the future, add a test case for a symlink pointing to a file
+# On systems with symlink support, we follow symlinks when embedding files.
+# TODO: add a test case for a symlink pointing to a file
 # outside of the current module, as that should likely be forbidden.
 [!symlink] stop
 cd symlink

cmd/cue/cmd/testdata/script/embed_file_err.txtar

@@ -1,7 +1,6 @@
 # Test what happens when there is an error an embedded file.
 # The error should mention the name of the file where the error is.
 
-env CUE_EXPERIMENT=embed
 ! exec cue vet
 cmp stderr want-stderr
 ! exec cue export

cmd/cue/cmd/testdata/script/embed_mod.txtar

@@ -1,5 +1,3 @@
-env CUE_EXPERIMENT=embed
-
 exec cue mod tidy
 exec cue eval ./acme/foo
 cmp stdout out/eval

cmd/cue/cmd/testdata/script/embed_windows.txtar

@@ -1,5 +1,3 @@
-env CUE_EXPERIMENT=embed
-
 [!windows] cp reuse.json 'star/*.json'
 [!windows] exec cue export --out cue
 [!windows] cmp stdout out/export-unix

encoding/jsonschema/internal/externaltest/tests.go

@@ -88,7 +88,6 @@ func ReadTestDir(dir string) (tests map[string][]*Schema, err error) {
 		}
 		return nil, err
 	}
-	os.Setenv("CUE_EXPERIMENT", "embed")
 	inst := load.Instances([]string{"."}, &load.Config{
 		Dir: dir,
 		// Just like in the cue/load tests, prevent Go tests from walking up to the root

internal/cueexperiment/exp.go

@@ -20,7 +20,7 @@ var Flags struct {
 	EvalV3 bool
 
 	// Embed enables file embedding.
-	Embed bool
+	Embed bool `envflag:"default:true"`
 
 	// DecodeInt64 changes [cuelang.org/go/cue.Value.Decode] to choose
 	// `int64` rather than `int` as the default type for CUE integer values