DispatchError::Module is now a tuple variant in latest Substrate (#439)

* ModuleError is now a tuple variant

* more robust pointer to DispatchError

* backward compat

* clippy

* cargo fmt

* abort_call_site and simplify path comparison

* clippy

codegen/src/api/errors.rs

@@ -19,7 +19,9 @@ use proc_macro2::{
     Span as Span2,
     TokenStream as TokenStream2,
 };
+use proc_macro_error::abort_call_site;
 use quote::quote;
+use scale_info::TypeDef;
 
 /// Tokens which allow us to provide static error information in the generated output.
 pub struct ErrorDetails {
@@ -71,17 +73,48 @@ pub fn generate_error_details(metadata: &RuntimeMetadataV14) -> ErrorDetails {
         }
     });
 
-    ErrorDetails {
-        type_def: quote! {
-            pub struct ErrorDetails {
-                pub pallet: &'static str,
-                pub error: &'static str,
-                pub docs: &'static str,
-            }
-        },
-        dispatch_error_impl_fn: quote! {
+    let dispatch_error_def = metadata
+        .types
+        .types()
+        .iter()
+        .find(|&ty| ty.ty().path().segments() == ["sp_runtime", "DispatchError"])
+        .unwrap_or_else(|| {
+            abort_call_site!("sp_runtime::DispatchError type expected in metadata")
+        })
+        .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 dispatch_error_impl_fn = if module_variant_is_struct {
+        quote! {
             pub fn details(&self) -> Option<ErrorDetails> {
-                if let Self::Module { index, error } = self {
+                if let Self::Module { error, index } = self {
                     match (index, error) {
                         #( #match_body_items ),*,
                         _ => None
@@ -90,7 +123,31 @@ pub fn generate_error_details(metadata: &RuntimeMetadataV14) -> ErrorDetails {
                     None
                 }
             }
+        }
+    } else {
+        quote! {
+            pub fn details(&self) -> Option<ErrorDetails> {
+                if let Self::Module (module_error) = self {
+                    match (module_error.index, module_error.error) {
+                        #( #match_body_items ),*,
+                        _ => None
+                    }
+                } else {
+                    None
+                }
+            }
+        }
+    };
+
+    ErrorDetails {
+        type_def: quote! {
+            pub struct ErrorDetails {
+                pub pallet: &'static str,
+                pub error: &'static str,
+                pub docs: &'static str,
+            }
         },
+        dispatch_error_impl_fn,
     }
 }
 

codegen/src/api/mod.rs

@@ -284,7 +284,7 @@ impl RuntimeGenerator {
                 #types_mod
 
                 /// The default error type returned when there is a runtime issue.
-                pub type DispatchError = self::runtime_types::sp_runtime::DispatchError;
+                pub type DispatchError = #types_mod_ident::sp_runtime::DispatchError;
 
                 // Statically generate error information so that we don't need runtime metadata for it.
                 #error_type