Don't swallow the other fields of the diagnostic code

Author: jneem

src/cargo/core/compiler/mod.rs

@@ -2168,12 +2168,14 @@ fn on_stderr_line_inner(
                 rendered: String,
                 #[serde(flatten, borrow)]
                 other: std::collections::BTreeMap<Cow<'a, str>, serde_json::Value>,
-                code: Option<DiagnosticCode>,
+                code: Option<DiagnosticCode<'a>>,
             }
 
             #[derive(serde::Deserialize, serde::Serialize)]
-            struct DiagnosticCode {
+            struct DiagnosticCode<'a> {
                 code: String,
+                #[serde(flatten, borrow)]
+                other: std::collections::BTreeMap<Cow<'a, str>, serde_json::Value>,
             }
 
             if let Ok(mut error) =

tests/testsuite/test.rs

@@ -4474,7 +4474,8 @@ fn json_diagnostic_includes_explanation() {
       "$message_type": "diagnostic",
       "children": "{...}",
       "code": {
-        "code": "E0764"
+        "code": "E0764",
+        "explanation": "{...}"
       },
       "level": "error",
       "message": "mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed",