internal/cueexperiment: prevent disabling modules experiment

This change deprecates the modules experiment flag, meaning
that modules will always be enabled. We do not yet remove the code to
deal with disabled modules, meaning that it will be straightforward
to revert this change if it turns out to be necessary.

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: I846ea4cdbe15c871c3cd92d40cbc5b8809b7b67d
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1200580
Reviewed-by: Daniel Martí <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: rogpeppe

cmd/cue/cmd/testdata/script/def_proto.txtar

@@ -1,7 +1,3 @@
-env CUE_EXPERIMENT=modules=0
-exec cue def policy.proto -p api -I include
-cmp stdout expect-stdout
-
 env CUE_EXPERIMENT=modules
 exec cue def policy.proto -p api -I include
 cmp stdout expect-stdout

cmd/cue/cmd/testdata/script/modinit_majorversion.txtar

@@ -1,14 +1,10 @@
 env-fill want-module.cue
 env-fill want-module-experiment.cue
 
-# Without the experiment, the major version is allowed,
-# even though it's not particularly useful.
-# It feels unnecessary to ask the user to re-run with the experiment.
+# No way of disabling the modules experiment.
 env CUE_EXPERIMENT=modules=0
-exec cue mod init foo.com/bar@v1
-cmp cue.mod/module.cue want-module.cue
-exists cue.mod/usr
-exists cue.mod/pkg
+! exec cue mod init foo.com/bar@v1
+stderr 'cannot change default value of deprecated flag "modules"'
 
 # With the experiment, it works as expected.
 env CUE_EXPERIMENT=modules

cmd/cue/cmd/testdata/script/modinit_nomajorversion.txtar

@@ -1,12 +1,10 @@
 env-fill want-module.cue
 env-fill want-module-experiment.cue
 
-# Without the experiment, we use the module path as-is.
-env CUE_EXPERIMENT=modules=false
-exec cue mod init foo.com/bar
-cmp cue.mod/module.cue want-module.cue
-exists cue.mod/usr
-exists cue.mod/pkg
+# No way of disabling the modules experiment.
+env CUE_EXPERIMENT=modules=0
+! exec cue mod init foo.com/bar
+stderr 'cannot change default value of deprecated flag "modules"'
 
 # With the experiment, although the major version will be implied
 # as v0, it's still omitted so that there's a possibility of compatibility

cmd/cue/cmd/testdata/script/modpublish_registry_not_enabled.txtar

@@ -2,4 +2,4 @@ env CUE_EXPERIMENT=modules=false
 ! exec cue mod publish v1.0.0
 cmp stderr want-stderr
 -- want-stderr --
-modules experiment not enabled (enable with CUE_EXPERIMENT=modules)
+cannot parse CUE_EXPERIMENT: cannot change default value of deprecated flag "modules"

cmd/cue/cmd/testdata/script/modtidy_registry_not_enabled.txtar

@@ -3,4 +3,4 @@ env CUE_EXPERIMENT=modules=0
 ! exec cue mod tidy
 cmp stderr want-stderr
 -- want-stderr --
-modules experiment not enabled (enable with CUE_EXPERIMENT=modules)
+cannot parse CUE_EXPERIMENT: cannot change default value of deprecated flag "modules"

cmd/cue/cmd/testdata/script/registry_modules_disabled.txtar

@@ -1,35 +1,5 @@
-# When CUE_EXPERIMENT is disabled, the CUE_REGISTRY
-# variable is ignored, as are the new fields in module.cue
+# When CUE_EXPERIMENT is disabled, we cannot use the cue command.
 
 env CUE_EXPERIMENT=modules=false
-exec cue export .
-cmp stdout expect-stdout
-
--- expect-stdout --
-"cue.mod/pkg source"
--- main.cue --
-package main
-import "example.com/e"
-
-e.foo
-
--- cue.mod/module.cue --
-module: "test.org"
-language: version: "v0.9.0"
-// This should be ignored.
-deps: "example.com/e": v: "v0.0.1"
--- cue.mod/pkg/example.com/e/cue.mod/module.cue --
-module: "example.com/e"
-language: version: "v0.8.0"
--- cue.mod/pkg/example.com/e/main.cue --
-package e
-foo: "cue.mod/pkg source"
-
--- _registry/example.com_e_v0.0.1/cue.mod/module.cue --
-module: "example.com/e@v0"
-language: version: "v0.8.0"
-
--- _registry/example.com_e_v0.0.1/main.cue --
-package e
-
-foo: "registry source"
+! exec cue export .
+stderr 'cannot change default value of deprecated flag "modules"'

cmd/cue/cmd/testdata/script/registry_modules_disabled_warning.txtar

@@ -11,7 +11,7 @@ import (
 // When adding, deleting, or modifying entries below,
 // update cmd/cue/cmd/help.go as well for `cue help environment`.
 var Flags struct {
-	Modules bool `envflag:"default:true"`
+	Modules bool `envflag:"deprecated,default:true"`
 
 	// YAMLV3Decoder swaps the old internal/third_party/yaml decoder with the new
 	// decoder implemented in internal/encoding/yaml on top of yaml.v3.

internal/cueexperiment/exp.go

@@ -23,10 +23,15 @@ func TestInit(t *testing.T) {
 	qt.Assert(t, qt.IsTrue(Flags.Modules))
 	qt.Assert(t, qt.IsTrue(Flags.YAMLV3Decoder))
 
-	// Check that we can disable all experiments.
-	t.Setenv("CUE_EXPERIMENT", "modules=0,yamlv3decoder=0")
+	// Check that we can disable the YAML v3 experiment.
+	t.Setenv("CUE_EXPERIMENT", "yamlv3decoder=0")
 	err = initAlways()
 	qt.Assert(t, qt.IsNil(err))
-	qt.Assert(t, qt.IsFalse(Flags.Modules))
+	qt.Assert(t, qt.IsTrue(Flags.Modules))
 	qt.Assert(t, qt.IsFalse(Flags.YAMLV3Decoder))
+
+	// Check that we cannot disable the modules experiment.
+	t.Setenv("CUE_EXPERIMENT", "modules=0")
+	err = initAlways()
+	qt.Assert(t, qt.ErrorMatches(err, `cannot parse CUE_EXPERIMENT: cannot change default value of deprecated flag "modules"`))
 }