lang: Ignore unnamed structs instead of panic (#605)

CHANGELOG.md

@@ -11,6 +11,10 @@ incremented for features.
 
 ## [Unreleased]
 
+### Features
+
+* lang: Ignore `Unnamed` structs instead of panic ([#605](https://github.com/project-serum/anchor/pull/605)).
+
 ## [0.13.2] - 2021-08-11
 
 ### Fixes

lang/syn/src/idl/file.rs

@@ -384,7 +384,8 @@ fn parse_ty_defs(ctx: &CrateContext) -> Result<Vec<IdlTypeDefinition>> {
                         })
                     })
                     .collect::<Result<Vec<IdlField>>>(),
-                _ => panic!("Only named structs are allowed."),
+                syn::Fields::Unnamed(_) => return None,
+                _ => panic!("Empty structs are allowed."),
             };
 
             Some(fields.map(|fields| IdlTypeDefinition {