feat(tiller): add fromYaml to template functions

This adds a fromYaml template function.

Closes #1604

pkg/chartutil/files.go

@@ -174,3 +174,18 @@ func ToYaml(v interface{}) string {
 	}
 	return string(data)
 }
+
+// FromYaml converts a YAML document into a map[string]interface{}.
+//
+// This is not a general-purpose YAML parser, and will not parse all valid
+// YAML documents. Additionally, because its intended use is within templates
+// it tolerates errors. It will insert the returned error message string into
+// m["error"] in the returned map.
+func FromYaml(str string) map[string]interface{} {
+	m := map[string]interface{}{}
+
+	if err := yaml.Unmarshal([]byte(str), &m); err != nil {
+		m["Error"] = err.Error()
+	}
+	return m
+}

pkg/chartutil/files_test.go

@@ -110,3 +110,34 @@ func TestToYaml(t *testing.T) {
 		t.Errorf("Expected %q, got %q", expect, got)
 	}
 }
+
+func TestFromYaml(t *testing.T) {
+	doc := `hello: world
+one:
+  two: three
+`
+	dict := FromYaml(doc)
+	if err, ok := dict["Error"]; ok {
+		t.Fatalf("Parse error: %s", err)
+	}
+
+	if len(dict) != 2 {
+		t.Fatal("expected two elements.")
+	}
+
+	world := dict["hello"]
+	if world.(string) != "world" {
+		t.Fatal("Expected the world. Is that too much to ask?")
+	}
+
+	// This should fail because we don't currently support lists:
+	doc2 := `
+- one
+- two
+- three
+`
+	dict = FromYaml(doc2)
+	if _, ok := dict["Error"]; !ok {
+		t.Fatal("Expected parser error")
+	}
+}

pkg/engine/engine.go

@@ -70,7 +70,8 @@ func FuncMap() template.FuncMap {
 
 	// Add some extra functionality
 	extra := template.FuncMap{
-		"toYaml": chartutil.ToYaml,
+		"toYaml":   chartutil.ToYaml,
+		"fromYaml": chartutil.FromYaml,
 
 		// This is a placeholder for the "include" function, which is
 		// late-bound to a template. By declaring it here, we preserve the

pkg/engine/engine_test.go

@@ -49,7 +49,7 @@ func TestFuncMap(t *testing.T) {
 	}
 
 	// Test for Engine-specific template functions.
-	expect := []string{"include", "toYaml"}
+	expect := []string{"include", "toYaml", "fromYaml"}
 	for _, f := range expect {
 		if _, ok := fns[f]; !ok {
 			t.Errorf("Expected add-on function %q", f)