cmd/cue: add a testscript for CUE_DEBUG=sortfields working with the Go API

It currently does not; we will fix this in the following commit.
We write this test as part of the cmd/cue testscript suite
given that we already have multiple scripts which smoke test
whether CUE_EXPERIMENT and CUE_DEBUG are wired through properly,
such as sortfields.txtar and also dev.txtar for CUE_EXPERIMENT=evalv3.

While here, since the export output with sortfields is the same
on evalv2 and evalv3, we can deduplicate one of the output files
in sortfields.txtar.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I0895966789bec41db859e635ecacb7d08d0d8318
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1205201
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mvdan

cmd/cue/cmd/script_test.go

@@ -45,6 +45,8 @@ import (
 	"golang.org/x/oauth2"
 	"golang.org/x/tools/txtar"
 
+	"cuelang.org/go/cue"
+	"cuelang.org/go/cue/cuecontext"
 	"cuelang.org/go/cue/errors"
 	"cuelang.org/go/cue/parser"
 	"cuelang.org/go/internal/cuetest"
@@ -388,6 +390,12 @@ func TestX(t *testing.T) {
 }
 
 func TestMain(m *testing.M) {
+	check := func(err error) {
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+	}
 	os.Exit(testscript.RunMain(m, map[string]func() int{
 		"cue": Main,
 		// Until https://github.com/rogpeppe/go-internal/issues/93 is fixed,
@@ -411,10 +419,26 @@ func TestMain(m *testing.M) {
 			return 0
 		},
 		"testcmd": func() int {
-			if err := testCmd(); err != nil {
-				fmt.Fprintln(os.Stderr, err)
-				return 1
-			}
+			err := testCmd()
+			check(err)
+			return 0
+		},
+		// Like `cue export`, but as a standalone Go program which doesn't
+		// go through cmd/cue's setup of cuecontext and the evaluator.
+		// Useful to check what the export behavior is for Go API users,
+		// for example in relation to env vars like CUE_EXPERIMENT or CUE_DEBUG.
+		// Only works with cue stdin and json stdout for simplicity.
+		"cuectx_export": func() int {
+			input, err := io.ReadAll(os.Stdin)
+			check(err)
+			ctx := cuecontext.New()
+			v := ctx.CompileBytes(input)
+			err = v.Validate(cue.Concrete(true))
+			check(err)
+			enc := json.NewEncoder(os.Stdout)
+			enc.SetIndent("", "    ")
+			err = enc.Encode(v)
+			check(err)
 			return 0
 		},
 	}))

cmd/cue/cmd/testdata/script/sortfields.txtar

@@ -23,7 +23,13 @@ cmp stdout eval.stdout
 # Just to double check, ensure it also works for evalv3.
 env CUE_EXPERIMENT=evalv3
 exec cue export input.cue
-cmp stdout export-evalv3.stdout
+cmp stdout export.stdout
+
+# Also ensure that it's wired up for the Go API.
+# TODO: it is not, currently.
+stdin input.cue
+exec cuectx_export
+cmp stdout export-unsorted.stdout
 
 -- input.cue --
 c: true
@@ -53,16 +59,6 @@ b: y: true
     },
     "c": true
 }
--- export-evalv3.stdout --
-{
-    "a": true,
-    "b": {
-        "x": true,
-        "y": true,
-        "z": true
-    },
-    "c": true
-}
 -- export-yaml.stdout --
 a: true
 b: