cue/interpreter/embed: require type if glob extension not specified

Per the design in https://cuelang.org/discussion/3264, we require the
type argument to be specified if the extension provided in a glob
pattern is not fully specified.

The current implementation does not implement that behaviour. This CL
corrects that.

Fixes #3274.

Signed-off-by: Paul Jolly <[email protected]>
Change-Id: If07d966fd51fce0634bd4da38853cf974ad2d202
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1197339
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
Reviewed-by: Marcel van Lohuizen <[email protected]>

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

@@ -50,6 +50,12 @@ noTranslateBS: _ @embed(file="x\\test.json")
 autoCUEfiletype: _ @embed(file="x.cue")
 explicitCUEfiletype: _ @embed(file=xcue, type=cue)
 
+// intentional missing type arg
+unspecifiedFiletype1: _ @embed(glob=x/*.*)
+unspecifiedFiletype2: _ @embed(glob=x/*)
+unspecifiedFiletype3: _ @embed(glob=x/*.?son)
+unspecifiedFiletype4: _ @embed(glob=x/*.[j]son)
+
 -- test.json --
 { "x": 34 }
 -- test.ldjson --
@@ -116,3 +122,11 @@ x: 5
     ./test.cue:43:20
 @embed: encoding "cue" not (yet) supported:
     ./test.cue:44:24
+@embed: extension not fully specified; type argument required:
+    ./test.cue:47:25
+@embed: extension not fully specified; type argument required:
+    ./test.cue:48:25
+@embed: extension not fully specified; type argument required:
+    ./test.cue:49:25
+@embed: extension not fully specified; type argument required:
+    ./test.cue:50:25

cue/interpreter/embed/embed.go

@@ -216,6 +216,16 @@ func (c *compiler) processGlob(glob, scope string, schema adt.Value) (adt.Expr,
 		return nil, errors.Newf(c.pos, "double star not (yet) supported in glob")
 	}
 
+	// If we do not have a type, ensure the extension of the base is fully
+	// specified, i.e. does not contain any meta characters as specified by
+	// path.Match.
+	if scope == "" {
+		ext := path.Ext(path.Base(glob))
+		if ext == "" || strings.ContainsAny(ext, "*?[\\") {
+			return nil, errors.Newf(c.pos, "extension not fully specified; type argument required")
+		}
+	}
+
 	m := &adt.StructLit{}
 
 	matches, err := fs.Glob(c.fs, glob)