Use the generated DispatchError instead of the hardcoded Substrate one

codegen/src/api/calls.rs

@@ -68,7 +68,7 @@ pub fn generate_calls(
                 pub fn #fn_name(
                     &self,
                     #( #call_fn_args, )*
-                ) -> ::subxt::SubmittableExtrinsic<'a, T, E, A, #call_struct_name> {
+                ) -> ::subxt::SubmittableExtrinsic<'a, T, X, A, #call_struct_name, DispatchError> {
                     let call = #call_struct_name { #( #call_args, )* };
                     ::subxt::SubmittableExtrinsic::new(self.client, call)
                 }
@@ -80,17 +80,20 @@ pub fn generate_calls(
     quote! {
         pub mod calls {
             use super::#types_mod_ident;
+
+            type DispatchError = #types_mod_ident::sp_runtime::DispatchError;
+
             #( #call_structs )*
 
-            pub struct TransactionApi<'a, T: ::subxt::Config, E, A> {
+            pub struct TransactionApi<'a, T: ::subxt::Config, X, A> {
                 client: &'a ::subxt::Client<T>,
-                marker: ::core::marker::PhantomData<(E, A)>,
+                marker: ::core::marker::PhantomData<(X, A)>,
             }
 
-            impl<'a, T, E, A> TransactionApi<'a, T, E, A>
+            impl<'a, T, X, A> TransactionApi<'a, T, X, A>
             where
                 T: ::subxt::Config,
-                E: ::subxt::SignedExtra<T>,
+                X: ::subxt::SignedExtra<T>,
                 A: ::subxt::AccountData<T>,
             {
                 pub fn new(client: &'a ::subxt::Client<T>) -> Self {

codegen/src/api/errors.rs

@@ -0,0 +1,162 @@
+// Copyright 2019-2022 Parity Technologies (UK) Ltd.
+// This file is part of subxt.
+//
+// subxt is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// subxt is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+use frame_metadata::v14::RuntimeMetadataV14;
+use proc_macro2::{
+    Span as Span2,
+    TokenStream as TokenStream2,
+};
+use quote::quote;
+
+/// Tokens which allow us to provide static error information in the generated output.
+pub struct ErrorDetails {
+    /// This type definition will be used in the `dispatch_error_impl_fn` and is
+    /// expected to be generated somewhere in scope for that to be possible.
+    pub type_def: TokenStream2,
+    // A function which will live in an impl block for our `DispatchError`,
+    // to statically return details for known error types:
+    pub dispatch_error_impl_fn: TokenStream2,
+}
+
+impl ErrorDetails {
+    fn emit_compile_error(err: &str) -> ErrorDetails {
+        let err_lit_str = syn::LitStr::new(err, Span2::call_site());
+        ErrorDetails {
+            type_def: quote!(),
+            dispatch_error_impl_fn: quote!(compile_error!(#err_lit_str)),
+        }
+    }
+}
+
+/// The purpose of this is to enumerate all of the possible `(module_index, error_index)` error
+/// variants, so that we can convert `u8` error codes inside a generated `DispatchError` into
+/// nicer error strings with documentation. To do this, we emit the type we'll return instances of,
+/// and a function that returns such an instance for all of the error codes seen in the metadata.
+pub fn generate_error_details(metadata: &RuntimeMetadataV14) -> ErrorDetails {
+    let errors = match pallet_errors(metadata) {
+        Ok(errors) => errors,
+        Err(e) => {
+            let err_string =
+                format!("Failed to generate error details from metadata: {}", e);
+            return ErrorDetails::emit_compile_error(&err_string)
+        }
+    };
+
+    let match_body_items = errors.into_iter().map(|err| {
+        let docs = err.docs;
+        let pallet_index = err.pallet_index;
+        let error_index = err.error_index;
+        let pallet_name = err.pallet;
+        let error_name = err.error;
+
+        quote! {
+            (#pallet_index, #error_index) => Some(ErrorDetails {
+                pallet: #pallet_name,
+                error: #error_name,
+                docs: #docs
+            })
+        }
+    });
+
+    ErrorDetails {
+        type_def: quote! {
+            pub struct ErrorDetails {
+                pub pallet: &'static str,
+                pub error: &'static str,
+                pub docs: &'static str,
+            }
+        },
+        dispatch_error_impl_fn: quote! {
+            pub fn details(&self) -> Option<ErrorDetails> {
+                if let Self::Module { index, error } = self {
+                    match (index, error) {
+                        #( #match_body_items ),*,
+                        _ => None
+                    }
+                } else {
+                    None
+                }
+            }
+        },
+    }
+}
+
+fn pallet_errors(
+    metadata: &RuntimeMetadataV14,
+) -> Result<Vec<ErrorMetadata>, InvalidMetadataError> {
+    let get_type_def_variant = |type_id: u32| {
+        let ty = metadata
+            .types
+            .resolve(type_id)
+            .ok_or(InvalidMetadataError::MissingType(type_id))?;
+        if let scale_info::TypeDef::Variant(var) = ty.type_def() {
+            Ok(var)
+        } else {
+            Err(InvalidMetadataError::TypeDefNotVariant(type_id))
+        }
+    };
+
+    let mut pallet_errors = vec![];
+    for pallet in &metadata.pallets {
+        let error = match &pallet.error {
+            Some(err) => err,
+            None => continue,
+        };
+
+        let type_def_variant = get_type_def_variant(error.ty.id())?;
+        for var in type_def_variant.variants().iter() {
+            pallet_errors.push(ErrorMetadata {
+                pallet_index: pallet.index,
+                error_index: var.index(),
+                pallet: pallet.name.clone(),
+                error: var.name().clone(),
+                docs: var.docs().join("\n"),
+            });
+        }
+    }
+
+    Ok(pallet_errors)
+}
+
+/// Information about each error that we find in the metadata;
+/// used to generate the static error information.
+#[derive(Clone, Debug)]
+struct ErrorMetadata {
+    pub pallet_index: u8,
+    pub error_index: u8,
+    pub pallet: String,
+    pub error: String,
+    pub docs: String,
+}
+
+#[derive(Debug)]
+enum InvalidMetadataError {
+    MissingType(u32),
+    TypeDefNotVariant(u32),
+}
+
+impl std::fmt::Display for InvalidMetadataError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            InvalidMetadataError::MissingType(n) => {
+                write!(f, "Type {} missing from type registry", n)
+            }
+            InvalidMetadataError::TypeDefNotVariant(n) => {
+                write!(f, "Type {} was not a variant/enum type", n)
+            }
+        }
+    }
+}

codegen/src/api/mod.rs

@@ -15,6 +15,7 @@
 // along with subxt.  If not, see <http://www.gnu.org/licenses/>.
 
 mod calls;
+mod errors;
 mod events;
 mod storage;
 
@@ -216,6 +217,10 @@ impl RuntimeGenerator {
                     pallet.calls.as_ref().map(|_| pallet_mod_name)
                 });
 
+        let error_details = errors::generate_error_details(&self.metadata);
+        let error_type = error_details.type_def;
+        let error_fn = error_details.dispatch_error_impl_fn;
+
         quote! {
             #[allow(dead_code, unused_imports, non_camel_case_types)]
             pub mod #mod_ident {
@@ -227,6 +232,15 @@ impl RuntimeGenerator {
                 /// constructing a transaction.
                 pub type DefaultAccountData = self::system::storage::Account;
 
+                /// The default error type returned when there is a runtime issue.
+                pub type DispatchError = self::runtime_types::sp_runtime::DispatchError;
+
+                // Statically generate error information so that we don't need runtime metadata for it.
+                #error_type
+                impl DispatchError {
+                    #error_fn
+                }
+
                 impl ::subxt::AccountData<::subxt::DefaultConfig> for DefaultAccountData {
                     fn nonce(result: &<Self as ::subxt::StorageEntry>::Value) -> <::subxt::DefaultConfig as ::subxt::Config>::Index {
                         result.nonce
@@ -236,31 +250,31 @@ impl RuntimeGenerator {
                     }
                 }
 
-                pub struct RuntimeApi<T: ::subxt::Config, E> {
+                pub struct RuntimeApi<T: ::subxt::Config, X> {
                     pub client: ::subxt::Client<T>,
-                    marker: ::core::marker::PhantomData<E>,
+                    marker: ::core::marker::PhantomData<X>,
                 }
 
-                impl<T, E> ::core::convert::From<::subxt::Client<T>> for RuntimeApi<T, E>
+                impl<T, X> ::core::convert::From<::subxt::Client<T>> for RuntimeApi<T, X>
                 where
                     T: ::subxt::Config,
-                    E: ::subxt::SignedExtra<T>,
+                    X: ::subxt::SignedExtra<T>,
                 {
                     fn from(client: ::subxt::Client<T>) -> Self {
                         Self { client, marker: ::core::marker::PhantomData }
                     }
                 }
 
-                impl<'a, T, E> RuntimeApi<T, E>
+                impl<'a, T, X> RuntimeApi<T, X>
                 where
                     T: ::subxt::Config,
-                    E: ::subxt::SignedExtra<T>,
+                    X: ::subxt::SignedExtra<T>,
                 {
                     pub fn storage(&'a self) -> StorageApi<'a, T> {
                         StorageApi { client: &self.client }
                     }
 
-                    pub fn tx(&'a self) -> TransactionApi<'a, T, E, DefaultAccountData> {
+                    pub fn tx(&'a self) -> TransactionApi<'a, T, X, DefaultAccountData> {
                         TransactionApi { client: &self.client, marker: ::core::marker::PhantomData }
                     }
                 }
@@ -280,19 +294,19 @@ impl RuntimeGenerator {
                     )*
                 }
 
-                pub struct TransactionApi<'a, T: ::subxt::Config, E, A> {
+                pub struct TransactionApi<'a, T: ::subxt::Config, X, A> {
                     client: &'a ::subxt::Client<T>,
-                    marker: ::core::marker::PhantomData<(E, A)>,
+                    marker: ::core::marker::PhantomData<(X, A)>,
                 }
 
-                impl<'a, T, E, A> TransactionApi<'a, T, E, A>
+                impl<'a, T, X, A> TransactionApi<'a, T, X, A>
                 where
                     T: ::subxt::Config,
-                    E: ::subxt::SignedExtra<T>,
+                    X: ::subxt::SignedExtra<T>,
                     A: ::subxt::AccountData<T>,
                 {
                     #(
-                        pub fn #pallets_with_calls(&self) -> #pallets_with_calls::calls::TransactionApi<'a, T, E, A> {
+                        pub fn #pallets_with_calls(&self) -> #pallets_with_calls::calls::TransactionApi<'a, T, X, A> {
                             #pallets_with_calls::calls::TransactionApi::new(self.client)
                         }
                     )*

codegen/src/api/storage.rs

@@ -50,6 +50,7 @@ pub fn generate_storage(
     quote! {
         pub mod storage {
             use super::#types_mod_ident;
+
             #( #storage_structs )*
 
             pub struct StorageApi<'a, T: ::subxt::Config> {
@@ -195,7 +196,7 @@ fn generate_storage_entry_fns(
             pub async fn #fn_name_iter(
                 &self,
                 hash: ::core::option::Option<T::Hash>,
-            ) -> ::core::result::Result<::subxt::KeyIter<'a, T, #entry_struct_ident>, ::subxt::Error> {
+            ) -> ::core::result::Result<::subxt::KeyIter<'a, T, #entry_struct_ident>, ::subxt::BasicError> {
                 self.client.storage().iter(hash).await
             }
         )
@@ -211,7 +212,7 @@ fn generate_storage_entry_fns(
             &self,
             #( #key_args, )*
             hash: ::core::option::Option<T::Hash>,
-        ) -> ::core::result::Result<#return_ty, ::subxt::Error> {
+        ) -> ::core::result::Result<#return_ty, ::subxt::BasicError> {
             let entry = #constructor;
             self.client.storage().#fetch(&entry, hash).await
         }

codegen/src/derives.rs

@@ -38,6 +38,7 @@ impl Default for GeneratedTypeDerives {
         let mut derives = Punctuated::new();
         derives.push(syn::parse_quote!(::subxt::codec::Encode));
         derives.push(syn::parse_quote!(::subxt::codec::Decode));
+        derives.push(syn::parse_quote!(Debug));
         Self::new(derives)
     }
 }