fix(capabilities): do not serialize None as null for list_changed (#341)

howardjohn · web-flow · commit 0a9a0a0b1f23 · 2025-07-30T11:08:31.000+08:00
The old form violates the spec, and all other `Option<bool>` fields also behave this way. Concretely https://github.com/upstash/context7/ fails without this change.
diff --git a/crates/rmcp/src/model/capabilities.rs b/crates/rmcp/src/model/capabilities.rs
@@ -36,6 +36,7 @@ pub struct ToolsCapability {
 #[serde(rename_all = "camelCase")]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RootsCapabilities {
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub list_changed: Option<bool>,
 }
 

Original file line number	Diff line number	Diff line change
`@@ -36,6 +36,7 @@ pub struct ToolsCapability {`
`36`	`36`	`#[serde(rename_all = "camelCase")]`
`37`	`37`	`#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]`
`38`	`38`	`pub struct RootsCapabilities {`
	`39`	`+ #[serde(skip_serializing_if = "Option::is_none")]`
`39`	`40`	`pub list_changed: Option<bool>,`
`40`	`41`	`}`
`41`	`42`