[chore] Clarify that Unmarshaler only supports structs (open-telemetry#13045)

mx-psi · web-flow · commit 943627b0fe72 · 2025-05-16T11:49:08.000Z
&lt;!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.--&gt;
#### Description

Clarifies usage of `confmap.Unmarshaler`. This is a limitation that
currently exists since mapstructure will fail to map between the types.
diff --git a/confmap/confmap.go b/confmap/confmap.go
@@ -543,6 +543,7 @@ func marshalerHookFunc(orig any) mapstructure.DecodeHookFuncValue {
 }
 
 // Unmarshaler interface may be implemented by types to customize their behavior when being unmarshaled from a Conf.
+// Only types with struct or pointer to struct kind are supported.
 type Unmarshaler interface {
 	// Unmarshal a Conf into the struct in a custom way.
 	// The Conf for this specific component may be nil or empty if no config available.

Original file line number	Diff line number	Diff line change
`@@ -543,6 +543,7 @@ func marshalerHookFunc(orig any) mapstructure.DecodeHookFuncValue {`
`543`	`543`	`}`
`544`	`544`
`545`	`545`	`// Unmarshaler interface may be implemented by types to customize their behavior when being unmarshaled from a Conf.`
	`546`	`+// Only types with struct or pointer to struct kind are supported.`
`546`	`547`	`type Unmarshaler interface {`
`547`	`548`	`// Unmarshal a Conf into the struct in a custom way.`
`548`	`549`	`// The Conf for this specific component may be nil or empty if no config available.`