pkg/encoding/yaml: implement UnmarshalStream

Change-Id: I587ef873531e40bf673b0675460a8da87c2a6a50
Signed-off-by: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/532280
Unity-Result: CUEcueckoo <cueckoo@cuelang.org>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Paul Jolly <paul@myitcv.io>

pkg/encoding/yaml/manual.go

@@ -71,11 +71,33 @@ func MarshalStream(v cue.Value) (string, error) {
 	return buf.String(), nil
 }
 
-// Unmarshal parses the YAML to a CUE instance.
+// Unmarshal parses the YAML to a CUE expression.
 func Unmarshal(data []byte) (ast.Expr, error) {
 	return yaml.Unmarshal("", data)
 }
 
+// UnmarshalStream parses the YAML to a CUE list expression on success.
+func UnmarshalStream(data []byte) (ast.Expr, error) {
+	d, err := yaml.NewDecoder("", data)
+	if err != nil {
+		return nil, err
+	}
+
+	a := []ast.Expr{}
+	for {
+		x, err := d.Decode()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+		a = append(a, x)
+	}
+
+	return ast.NewList(a...), nil
+}
+
 // Validate validates YAML and confirms it is an instance of the schema
 // specified by v. If the YAML source is a stream, every object must match v.
 func Validate(b []byte, v cue.Value) (bool, error) {

pkg/encoding/yaml/testdata/gen.txtar

@@ -12,6 +12,20 @@ t6: yaml.ValidatePartial("a: 2\n", {a:<5, b:int})
 t7: yaml.MarshalStream([{a: 1}, {b: 2}])
 t8: yaml.Marshal({b: int | *2})
 t9: yaml.MarshalStream([{a: 1}, {b: int | *2}])
+
+unmarshalStream: {
+	t1: yaml.UnmarshalStream("a: 1\n---\nb: 2")
+	t1: yaml.UnmarshalStream('a: 1\n---\nb: 2')
+	empty: yaml.UnmarshalStream('')
+	empty: yaml.UnmarshalStream("")
+	nums: yaml.UnmarshalStream('1\n---\n2')
+	nums: yaml.UnmarshalStream("1\n---\n2")
+	null1: yaml.UnmarshalStream('1\n---\n---\n2')
+	null1: yaml.UnmarshalStream("1\n---\n---\n2")
+	null2: yaml.UnmarshalStream('1\n---\n---\n2')
+	null2: yaml.UnmarshalStream("1\n---\n---\n2")
+}
+
 -- out/yaml --
 Errors:
 a: error in call to encoding/yaml.Validate: invalid value 4 (out of bound <3):
@@ -48,4 +62,15 @@ t9: """
 	b: 2
 
 	"""
+unmarshalStream: {
+	t1: [{
+		a: 1
+	}, {
+		b: 2
+	}]
+	empty: []
+	nums: [1, 2]
+	null1: [1, null, 2]
+	null2: [1, null, 2]
+}