Add yaml_decode to stdlib (#927)

* Implement yaml_decode with thanks to @djcode for most of the work.

* Update docs/sources/reference/stdlib/yaml_decode.md

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

---------

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

CHANGELOG.md

@@ -28,6 +28,8 @@ Main (unreleased)
 - Improved filesystem error handling when working with `loki.source.file` and `local.file_match`,
   which removes some false-positive error log messages on Windows (@thampiotr) 
 
+- Add `yaml_decode` to standard library. (@mattdurham, @djcode)
+
 ### Bugfixes
 
 - Fix panic when component ID contains `/` in `otelcomponent.MustNewType(ID)`.(@qclaogui)

docs/sources/reference/stdlib/yaml_decode.md

@@ -0,0 +1,39 @@
+---
+canonical: https://grafana.com/docs/alloy/latest/reference/stdlib/yaml_decode/
+description: Learn about yaml_decode
+title: yaml_decode
+---
+
+# yaml_decode
+
+The `yaml_decode` function decodes a string representing YAML into an {{< param "PRODUCT_NAME" >}}
+value. `yaml_decode` fails if the string argument provided cannot be parsed as
+YAML.
+
+A common use case of `yaml_decode` is to decode the output of a
+[`local.file`][] component to an {{< param "PRODUCT_NAME" >}} value.
+
+{{< admonition type="note" >}}
+ Remember to escape double quotes when passing YAML string literals to `yaml_decode`.
+
+For example, the YAML value `key: "value"` is properly represented by the string `"key: \"value\""`.
+{{< /admonition >}}
+
+## Examples
+
+```
+> yaml_decode("15")
+15
+> yaml_decode("[1, 2, 3]")
+[1, 2, 3]
+> yaml_decode("null")
+null
+> yaml_decode("key: value")
+{
+  key = "value",
+}
+> yaml_decode(local.file.some_file.content)
+"Hello, world!"
+```
+
+[`local.file`]: ../../components/local.file/

syntax/internal/stdlib/stdlib.go

@@ -11,6 +11,7 @@ import (
 	"github.com/grafana/alloy/syntax/internal/value"
 	"github.com/ohler55/ojg/jp"
 	"github.com/ohler55/ojg/oj"
+	"gopkg.in/yaml.v3"
 )
 
 // Identifiers holds a list of stdlib identifiers by name. All interface{}
@@ -83,6 +84,15 @@ var Identifiers = map[string]interface{}{
 		return res, nil
 	},
 
+	"yaml_decode": func(in string) (interface{}, error) {
+		var res interface{}
+		err := yaml.Unmarshal([]byte(in), &res)
+		if err != nil {
+			return nil, err
+		}
+		return res, nil
+	},
+
 	"json_path": func(jsonString string, path string) (interface{}, error) {
 		jsonPathExpr, err := jp.ParseString(path)
 		if err != nil {

syntax/vm/vm_stdlib_test.go

@@ -26,6 +26,11 @@ func TestVM_Stdlib(t *testing.T) {
 		{"json_decode array", `json_decode("[0, 1, 2]")`, []interface{}{float64(0), float64(1), float64(2)}},
 		{"json_decode nil field", `json_decode("{\"foo\": null}")`, map[string]interface{}{"foo": nil}},
 		{"json_decode nil array element", `json_decode("[0, null]")`, []interface{}{float64(0), nil}},
+		{"yaml_decode object", "yaml_decode(`foo: bar`)", map[string]interface{}{"foo": "bar"}},
+		{"yaml_decode array", "yaml_decode(`[0, 1, 2]`)", []interface{}{0, 1, 2}},
+		{"yaml_decode array float", "yaml_decode(`[0.0, 1.0, 2.0]`)", []interface{}{float64(0), float64(1), float64(2)}},
+		{"yaml_decode nil field", "yaml_decode(`foo: null`)", map[string]interface{}{"foo": nil}},
+		{"yaml_decode nil array element", `yaml_decode("[0, null]")`, []interface{}{0, nil}},
 	}
 
 	for _, tc := range tt {