cmd/cue: add test case for embedding of CUE file type files

For the initial implementation of embed we do not want to support
embedding of the CUE file type.

However the implementation currently allows it.

Ahead of fixing issue #3258 in a later CL to remove support for the CUE
file type, we add a test in embed_err.txtar. The test reflects the
current behaviour whereby a .cue file (or a file with an explicit CUE
file type) is not an error. This bug is fixed (and the test expectation
updated) in a later CL.

For #3258.

Signed-off-by: Paul Jolly <[email protected]>
Change-Id: I43ed4a3ce5c35c33a9256fa0af3304feb79f233c
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1197336
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>

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

@@ -47,6 +47,9 @@ norm4: _ @embed(file="x//test.json")
 
 noTranslateBS: _ @embed(file="x\\test.json")
 
+autoCUEfiletype: _ @embed(file="x.cue")
+explicitCUEfiletype: _ @embed(file=xcue, type=cue)
+
 -- test.json --
 { "x": 34 }
 -- test.ldjson --
@@ -67,6 +70,10 @@ a1: 2
 a1: 2
 -- test.textproto --
 a: 1
+-- x.cue --
+x: 5
+-- xcue --
+x: 5
 -- out/std --
 -- out/err --
 @embed: attribute must have file or glob field: