encoding/yaml: Add support for multi-document serialization

encoding/yaml/README.md

@@ -1,25 +1,27 @@
 # yaml
-yaml provides functions for working with yaml data
+yaml provides functions for working with yaml data.
 
 ## Functions
 
-#### `dumps(obj) string`
-serialize obj to a yaml string
+#### `dumps(obj, [obj, ...]) string`
+Serialize one or more objects to a yaml string.
+
+If more than one object is provided, the returned string will use
+YAML's [Multi-Document](https://yaml.org/spec/1.2.2/#example-two-documents-in-a-stream)
+format.
 
 **parameters:**
 
-| name | type | description |
-|------|------|-------------|
-| `obj` | `object` | input object |
+| name  | type     | description     |
+| ----- | -------- | --------------- |
+| `obj` | `object` | input object(s) |
 
 
 #### `loads(source) object`
-read a source yaml string to a starlark object
+Read a source yaml string to a Starlark object.
 
 **parameters:**
 
-| name | type | description |
-|------|------|-------------|
+| name     | type     | description               |
+| -------- | -------- | ------------------------- |
 | `source` | `string` | input string of yaml data |
-
-

encoding/yaml/testdata/test.star

@@ -1,6 +1,5 @@
-
-load('encoding/yaml.star', 'yaml')
-load('assert.star', 'assert')
+load("encoding/yaml.star", "yaml")
+load("assert.star", "assert")
 
 yaml_list = """- Apple
 - Orange
@@ -9,7 +8,7 @@ yaml_list = """- Apple
 """
 
 native_list = ["Apple", "Orange", "Strawberry", "Mango"]
-assert.eq(yaml.loads(yaml_list), native_list) 
+assert.eq(yaml.loads(yaml_list), native_list)
 assert.eq(yaml.dumps(native_list), yaml_list)
 
 yaml_dict = """martin:
@@ -22,3 +21,5 @@ native_dict = {"martin": {"name": "Martin D'vloper", "job": "Developer", "skill"
 assert.eq(yaml.loads(yaml_dict), native_dict)
 assert.eq(yaml.dumps(native_dict), yaml_dict)
 
+multidoc_yaml = "---\n".join([yaml_list, yaml_dict])
+assert.eq(yaml.dumps(native_list, native_dict), multidoc_yaml)

encoding/yaml/yaml.go

@@ -1,6 +1,7 @@
 package yaml
 
 import (
+	"bytes"
 	"sync"
 
 	"github.com/qri-io/starlib/util"
@@ -56,24 +57,39 @@ func Loads(thread *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kw
 
 // Dumps serializes a starlark object to a yaml string
 func Dumps(thread *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
-	var (
-		source starlark.Value
-	)
+	values := make([]starlark.Value, len(args))
+	valuePtrs := make([]interface{}, len(args))
 
-	err := starlark.UnpackArgs("dumps", args, kwargs, "source", &source)
-	if err != nil {
-		return starlark.None, err
+	for idx, _ := range values {
+		valuePtrs[idx] = &values[idx]
 	}
 
-	val, err := util.Unmarshal(source)
+	err := starlark.UnpackPositionalArgs("dumps", args, kwargs, 1, valuePtrs...)
 	if err != nil {
 		return starlark.None, err
 	}
 
-	data, err := yaml.Marshal(val)
-	if err != nil {
-		return starlark.None, err
+	buffer := new(bytes.Buffer)
+	for idx, value := range values {
+
+		goValue, err := util.Unmarshal(value)
+		if err != nil {
+			return starlark.None, err
+		}
+
+		rawBytes, err := yaml.Marshal(goValue)
+		if err != nil {
+			return starlark.None, err
+		}
+
+		buffer.Write(rawBytes)
+
+		// Add the YAML document separator if, and only if,
+		// there are more values to be serialized.
+		if idx < len(values)-1 {
+			buffer.WriteString("---\n")
+		}
 	}
 
-	return starlark.String(string(data)), nil
+	return starlark.String(buffer.String()), nil
 }