Handle sp_runtime::ModuleError substrate updates

codegen/src/api/errors.rs

@@ -18,7 +18,104 @@ use frame_metadata::v14::RuntimeMetadataV14;
 use proc_macro2::TokenStream as TokenStream2;
 use proc_macro_error::abort_call_site;
 use quote::quote;
-use scale_info::TypeDef;
+use scale_info::{
+    form::PortableForm,
+    Field,
+    TypeDef,
+};
+
+/// Different substrate versions will have a different `DispatchError::Module`.
+/// The following cases are ordered by versions.
+enum ModuleErrorType {
+    /// Case 1: `DispatchError::Module { index: u8, error: u8 }`
+    ///
+    /// This is the first supported `DispatchError::Module` format.
+    NamedField,
+    /// Case 2: `DispatchError::Module ( sp_runtime::ModuleError { index: u8, error: u8 } )`
+    ///
+    /// Substrate introduced `sp_runtime::ModuleError`, while keeping the error `u8`.
+    LegacyError,
+    /// Case 3: `DispatchError::Module ( sp_runtime::ModuleError { index: u8, error: [u8; 4] } )`
+    ///
+    /// The substrate error evolved into `[u8; 4]`.
+    ArrayError,
+}
+
+impl quote::ToTokens for ModuleErrorType {
+    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
+        let trait_fn_body = match self {
+            ModuleErrorType::NamedField => {
+                quote! {
+                    if let &Self::Module { index, error } = self {
+                        Some((index, error))
+                    } else {
+                        None
+                    }
+                }
+            }
+            ModuleErrorType::LegacyError => {
+                quote! {
+                    if let Self::Module (module_error) = self {
+                        Some((module_error.index, module_error.error))
+                    } else {
+                        None
+                    }
+                }
+            }
+            ModuleErrorType::ArrayError => {
+                quote! {
+                    if let Self::Module (module_error) = self {
+                        Some((module_error.index, module_error.error[0]))
+                    } else {
+                        None
+                    }
+                }
+            }
+        };
+
+        tokens.extend(trait_fn_body);
+    }
+}
+
+/// Determine the `ModuleError` type for the `ModuleErrorType::LegacyError` and
+/// `ModuleErrorType::ErrorArray` cases.
+fn module_error_type(
+    module_field: &Field<PortableForm>,
+    metadata: &RuntimeMetadataV14,
+) -> ModuleErrorType {
+    // Fields are named.
+    if module_field.name().is_some() {
+        return ModuleErrorType::NamedField
+    }
+
+    // Get the `sp_runtime::ModuleError` structure.
+    let module_err = metadata
+        .types
+        .resolve(module_field.ty().id())
+        .unwrap_or_else(|| {
+            abort_call_site!("sp_runtime::ModuleError type expected in metadata")
+        });
+
+    let error_type_def = match module_err.type_def() {
+        TypeDef::Composite(composite) => composite,
+        _ => abort_call_site!("sp_runtime::ModuleError type should be a composite type"),
+    };
+
+    // Get the error field from the `sp_runtime::ModuleError` structure.
+    let error_field = error_type_def
+        .fields()
+        .iter()
+        .find(|field| field.name() == Some(&"error".to_string()))
+        .unwrap_or_else(|| {
+            abort_call_site!("sp_runtime::ModuleError expected to contain error field")
+        });
+
+    if error_field.type_name() == Some(&"u8".to_string()) {
+        ModuleErrorType::LegacyError
+    } else {
+        ModuleErrorType::ArrayError
+    }
+}
 
 /// The aim of this is to implement the `::subxt::HasModuleError` trait for
 /// the generated `DispatchError`, so that we can obtain the module error details,
@@ -27,7 +124,7 @@ pub fn generate_has_module_error_impl(
     metadata: &RuntimeMetadataV14,
     types_mod_ident: &syn::Ident,
 ) -> TokenStream2 {
-    let dispatch_error_def = metadata
+    let dispatch_error = metadata
         .types
         .types()
         .iter()
@@ -38,55 +135,30 @@ pub fn generate_has_module_error_impl(
         .ty()
         .type_def();
 
-    // Slightly older versions of substrate have a `DispatchError::Module { index, error }`
-    // variant. Newer versions have something like a `DispatchError::Module (Details)` variant.
-    // We check to see which type of variant we're dealing with based on the metadata, and
-    // generate the correct code to handle either older or newer substrate versions.
-    let module_variant_is_struct = if let TypeDef::Variant(details) = dispatch_error_def {
-        let module_variant = details
-            .variants()
-            .iter()
-            .find(|variant| variant.name() == "Module")
-            .unwrap_or_else(|| {
-                abort_call_site!("DispatchError::Module variant expected in metadata")
-            });
-        let are_fields_named = module_variant
-            .fields()
-            .get(0)
-            .unwrap_or_else(|| {
-                abort_call_site!(
-                    "DispatchError::Module expected to contain 1 or more fields"
-                )
-            })
-            .name()
-            .is_some();
-        are_fields_named
-    } else {
-        false
-    };
-
-    let trait_fn_body = if module_variant_is_struct {
-        quote! {
-            if let &Self::Module { index, error } = self {
-                Some((index, error))
-            } else {
-                None
-            }
-        }
-    } else {
-        quote! {
-            if let Self::Module (module_error) = self {
-                Some((module_error.index, module_error.error))
-            } else {
-                None
-            }
+    // Get the `DispatchError::Module` variant (either struct or named fields).
+    let module_variant = match dispatch_error {
+        TypeDef::Variant(variant) => {
+            variant
+                .variants()
+                .iter()
+                .find(|variant| variant.name() == "Module")
+                .unwrap_or_else(|| {
+                    abort_call_site!("DispatchError::Module variant expected in metadata")
+                })
         }
+        _ => abort_call_site!("DispatchError expected to contain variant in metadata"),
     };
 
+    let module_field = module_variant.fields().get(0).unwrap_or_else(|| {
+        abort_call_site!("DispatchError::Module expected to contain 1 or more fields")
+    });
+
+    let error_type = module_error_type(module_field, metadata);
+
     quote! {
         impl ::subxt::HasModuleError for #types_mod_ident::sp_runtime::DispatchError {
             fn module_error_indices(&self) -> Option<(u8,u8)> {
-                #trait_fn_body
+                #error_type
             }
         }
     }