Fix getsourcecode bug

CHANGELOG.md

@@ -10,6 +10,7 @@
 - [#4067](https://github.com/blockscout/blockscout/pull/4067) - Display LP tokens USD value and custom metadata in tokens dropdown at address page
 
 ### Fixes
+- [#4320](https://github.com/blockscout/blockscout/pull/4320) - Fix absence of imported smart-contracts' source code in `getsourcecode` api method 
 - [#4274](https://github.com/blockscout/blockscout/pull/4302) - Fix search token-autocomplete
 - [#4316](https://github.com/blockscout/blockscout/pull/4316) - Fix `/decompiled-contracts` bug
 - [#4310](https://github.com/blockscout/blockscout/pull/4310) - Fix logo URL redirection, set font-family defaults for chart.js

apps/block_scout_web/lib/block_scout_web/views/api/rpc/contract_view.ex

@@ -1,7 +1,9 @@
 defmodule BlockScoutWeb.API.RPC.ContractView do
   use BlockScoutWeb, :view
 
+  alias BlockScoutWeb.AddressView
   alias BlockScoutWeb.API.RPC.RPCView
+  alias Explorer.Chain
   alias Explorer.Chain.{Address, DecompiledSmartContract, SmartContract}
 
   defguardp is_empty_string(input) when input == "" or input == nil
@@ -140,9 +142,34 @@ defmodule BlockScoutWeb.API.RPC.ContractView do
       |> Map.put_new(:CompilerVersion, Map.get(contract, :compiler_version, ""))
       |> Map.put_new(:OptimizationUsed, contract_optimization)
       |> Map.put_new(:EVMVersion, Map.get(contract, :evm_version, ""))
+      |> insert_additional_sources(address)
     end
   end
 
+  defp insert_additional_sources(output, address) do
+    additional_sources_from_twin = Chain.get_address_verified_twin_contract(address.hash).additional_sources
+
+    additional_sources =
+      if AddressView.smart_contract_verified?(address),
+        do: address.smart_contract_additional_sources,
+        else: additional_sources_from_twin
+
+    additional_sources_array =
+      if additional_sources,
+        do:
+          Enum.map(additional_sources, fn src ->
+            %{
+              Filename: src.file_name,
+              SourceCode: SmartContract.add_submitted_comment(src.contract_source_code, src.inserted_at)
+            }
+          end),
+        else: []
+
+    if additional_sources_array == [],
+      do: output,
+      else: Map.put_new(output, :AdditionalSources, additional_sources_array)
+  end
+
   defp prepare_contract(%Address{
          hash: hash,
          smart_contract: nil

apps/explorer/lib/explorer/chain.ex

@@ -3537,7 +3537,8 @@ defmodule Explorer.Chain do
         nil
 
       address ->
-        address_with_smart_contract = Repo.preload(address, [:smart_contract, :decompiled_smart_contracts])
+        address_with_smart_contract =
+          Repo.preload(address, [:smart_contract, :decompiled_smart_contracts, :smart_contract_additional_sources])
 
         if address_with_smart_contract.smart_contract do
           formatted_code = format_source_code_output(address_with_smart_contract.smart_contract)