test(derive): close fourth mutation shard

Prove generated form decoding for required, optional, and repeated controls plus bare, qualified, mismatched, and empty generic container boundaries.

req: form/004

req: diagnostics/003

req: test/022

req: test/023

hemx-derive/src/lib.rs

@@ -1023,13 +1023,13 @@ fn compile_error(message: &str) -> TokenStream {
 mod tests {
     use super::{
         add_app_registry_helper, add_component_register_helper, client_handler_has_inputs,
-        component_handler_names, expand_handler_function, form_contract_errors, form_fields,
-        form_impl_generics, form_model_type, form_resource_id, handle_params, handle_requires_form,
-        handler_form_model_type, handler_placement, handler_syms_path, has_form_param,
-        has_non_unit_return, is_type_named, join_contract_errors, missing_component_handlers,
-        missing_form_generated_files_message, missing_handle_params,
-        missing_handler_generated_files_message, parser_type, returns_result, syms_contains_handle,
-        HandlerPlacement,
+        component_handler_names, expand_handler_function, form_contract_errors, form_decode_fields,
+        form_fields, form_impl_generics, form_model_type, form_resource_id, generic_inner_type,
+        handle_params, handle_requires_form, handler_form_model_type, handler_placement,
+        handler_syms_path, has_form_param, has_non_unit_return, is_type_named,
+        join_contract_errors, missing_component_handlers, missing_form_generated_files_message,
+        missing_handle_params, missing_handler_generated_files_message, parser_type,
+        returns_result, syms_contains_handle, HandlerPlacement,
     };
     use quote::{quote, ToTokens};
     use syn::{parse_quote, ItemFn, Type};
@@ -1297,6 +1297,51 @@ mod tests {
                 "hemx form `profile` field `required_name` is required in HTML and must not be Option<_>",
             ]
         );
+
+        let decode_struct: syn::ItemStruct = parse_quote!(
+            struct Profile {
+                first: Option<String>,
+                tags: Vec<String>,
+                required_name: String,
+            }
+        );
+        let decoded = form_decode_fields(&path, "profile", &decode_struct)
+            .into_iter()
+            .map(|tokens| tokens.to_string())
+            .collect::<Vec<_>>();
+        assert_eq!(decoded.len(), 3);
+        assert!(decoded[0].contains("Some (__hemx_value) => Some"));
+        assert!(decoded[0].contains("None => None"));
+        assert!(decoded[1].contains("collect :: < Result < Vec < _ > , _ >> () ?"));
+        assert!(decoded[2].contains("missing form field"));
+
+        let option: Type = parse_quote!(Option<String>);
+        let qualified_vec: Type = parse_quote!(std::vec::Vec<u64>);
+        let plain: Type = parse_quote!(String);
+        assert_eq!(
+            generic_inner_type(&option, "Option")
+                .unwrap()
+                .to_token_stream()
+                .to_string(),
+            "String"
+        );
+        assert_eq!(
+            generic_inner_type(&qualified_vec, "Vec")
+                .unwrap()
+                .to_token_stream()
+                .to_string(),
+            "u64"
+        );
+        assert!(generic_inner_type(&option, "Vec").is_none());
+        assert!(generic_inner_type(&plain, "String").is_none());
+        let empty_path = Type::Path(syn::TypePath {
+            qself: None,
+            path: syn::Path {
+                leading_colon: None,
+                segments: Default::default(),
+            },
+        });
+        assert!(generic_inner_type(&empty_path, "Vec").is_none());
         std::fs::remove_file(path).unwrap();
         // test req: form/004 req: diagnostics/003
     }