cmd/cue: add TOML to a couple of help topics I forgot about

Neither `cue help filetypes` nor `cue help vet` listed it next to YAML,
which was an omission on my part when I added TOML support to cmd/cue.

This made me wonder for a second whether `cue vet` would support
TOML files out of the box already, so I added a test to confirm this.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I3f0d06f3234c5b4d566c47a912d062b5b16c3a1e
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1198859
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>

Author: mvdan

cmd/cue/cmd/help.go

@@ -491,6 +491,7 @@ var filetypeHelp = &cobra.Command{
     cue         .cue            CUE source files.
     json        .json           JSON files.
     yaml        .yaml/.yml      YAML files.
+    toml        .toml           TOML files
     jsonl       .jsonl/.ldjson  Line-separated JSON values.
     jsonschema                  JSON Schema.
     openapi                     OpenAPI schema.

cmd/cue/cmd/testdata/script/vet_data.txtar

@@ -1,8 +1,14 @@
 ! exec cue vet schema.cue data.yaml
-cmp stderr vet-stderr
+cmp stderr yaml-stderr
 
 ! exec cue export schema.cue data.yaml
-cmp stderr export-stderr
+cmp stderr yaml-stderr
+
+# Ensure this also works for other encodings.
+
+# TODO(mvdan): note that TOML lacks position information still.
+! exec cue vet schema.cue data.toml
+cmp stderr toml-stderr
 
 -- schema.cue --
 #Language: {
@@ -19,12 +25,20 @@ languages:
     name: dutch
   - tag: no
     name: Norwegian
-
--- vet-stderr --
+-- data.toml --
+[[languages]]
+name = 'English'
+tag = 'en'
+[[languages]]
+name = 'dutch'
+tag = 'nl'
+[[languages]]
+name = 'Norwegian'
+tag = 'no'
+-- yaml-stderr --
 languages.1.name: invalid value "dutch" (out of bound =~"^\\p{Lu}"):
     ./schema.cue:3:8
     ./data.yaml:5:11
--- export-stderr --
+-- toml-stderr --
 languages.1.name: invalid value "dutch" (out of bound =~"^\\p{Lu}"):
     ./schema.cue:3:8
-    ./data.yaml:5:11

cmd/cue/cmd/vet.go

@@ -36,6 +36,7 @@ currently supported:
   Format       Extensions
 	JSON       .json .jsonl .ndjson
 	YAML       .yaml .yml
+	TOML       .toml
 	TEXT       .txt  (validate a single string value)
 
 To activate this mode, the non-cue files must be explicitly mentioned on the