Codegen for custom values in metadata (#1117)

* work in progress

* add custom types access

* nit

* custom values client

* adjust light client

* adjust doc comments

* adjust book for custom values in code gen

* format and check docs

* work in progress

* add custom types access

* nit

* custom values client

* adjust light client

* codegen and validation

* adjust docs

* use ignore in docs in book

* change iter implementation

* use validation hash and other codegen changes

* add ui test for custom values codegen

* allow 'latest' metadata to be returned from the fallback code (#1127)

* nits

* fix validation check

* fix comments

* nits

---------

Co-authored-by: James Wilson <james@jsdw.me>

codegen/src/api/custom_values.rs

@@ -0,0 +1,61 @@
+// Copyright 2019-2023 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+use std::collections::HashSet;
+
+use crate::{types::TypeGenerator, CratePath};
+use heck::ToSnakeCase as _;
+use subxt_metadata::{CustomValueMetadata, Metadata};
+
+use proc_macro2::TokenStream as TokenStream2;
+use quote::{format_ident, quote};
+
+/// Generate the custom values mod, if there are any custom values in the metadata. Else returns None.
+pub fn generate_custom_values<'a>(
+    metadata: &'a Metadata,
+    type_gen: &'a TypeGenerator,
+    crate_path: &'a CratePath,
+) -> TokenStream2 {
+    let mut fn_names_taken = HashSet::new();
+    let custom = metadata.custom();
+    let custom_values_fns = custom.iter().filter_map(|custom_value| {
+        generate_custom_value_fn(custom_value, type_gen, crate_path, &mut fn_names_taken)
+    });
+
+    quote! {
+        pub struct CustomValuesApi;
+
+        impl CustomValuesApi {
+            #(#custom_values_fns)*
+        }
+    }
+}
+
+/// Generates runtime functions for the given API metadata.
+/// Returns None, if the name would not make for a valid identifier.
+fn generate_custom_value_fn(
+    custom_value: CustomValueMetadata,
+    type_gen: &TypeGenerator,
+    crate_path: &CratePath,
+    fn_names_taken: &mut HashSet<String>,
+) -> Option<TokenStream2> {
+    // names are transformed to snake case to make for good function identifiers.
+    let name = custom_value.name();
+    let fn_name = name.to_snake_case();
+    // Skip elements where the fn name is already occupied. E.g. if you have custom values with names "Foo" and "foo" in the metadata.
+    if fn_names_taken.contains(&fn_name) {
+        return None;
+    }
+    let fn_name_ident = format_ident!("{fn_name}");
+    fn_names_taken.insert(fn_name);
+
+    let custom_value_hash = custom_value.hash();
+    let return_ty = type_gen.resolve_type_path(custom_value.type_id());
+
+    Some(quote!(
+        pub fn #fn_name_ident() -> #crate_path::custom_values::StaticAddress<#return_ty> {
+            #crate_path::custom_values::StaticAddress::new_static(#name, [#(#custom_value_hash,)*])
+        }
+    ))
+}

codegen/src/api/mod.rs

@@ -6,6 +6,7 @@
 
 mod calls;
 mod constants;
+mod custom_values;
 mod errors;
 mod events;
 mod runtime_apis;
@@ -14,6 +15,7 @@ mod storage;
 use subxt_metadata::Metadata;
 
 use super::DerivesRegistry;
+use crate::api::custom_values::generate_custom_values;
 use crate::error::CodegenError;
 use crate::{
     ir,
@@ -469,6 +471,8 @@ impl RuntimeGenerator {
         let event_path = type_gen.resolve_type_path(self.metadata.outer_enums().event_enum_ty());
         let error_path = type_gen.resolve_type_path(self.metadata.outer_enums().error_enum_ty());
 
+        let custom_values = generate_custom_values(&self.metadata, &type_gen, &crate_path);
+
         Ok(quote! {
             #( #item_mod_attrs )*
             #[allow(dead_code, unused_imports, non_camel_case_types)]
@@ -521,6 +525,12 @@ impl RuntimeGenerator {
 
                 #apis_mod
 
+                pub fn custom() -> CustomValuesApi {
+                    CustomValuesApi
+                }
+
+                #custom_values
+
                 pub struct ConstantsApi;
                 impl ConstantsApi {
                     #(