Improve error message

When rejecting a transaction due to excessive authorizations on a
message, include the authorizations which were not necessary in the
reported error

libraries/chain/chain_controller.cpp

@@ -612,14 +612,16 @@ void chain_controller::validate_expiration(const SignedTransaction& trx) const
  *  The order of execution of precondition and apply can impact the validity of the
  *  entire message.
  */
-void chain_controller::process_message( const ProcessedTransaction& trx, AccountName code, const Message& message, MessageOutput& output) {
+void chain_controller::process_message(const ProcessedTransaction& trx, AccountName code,
+                                       const Message& message, MessageOutput& output) {
    apply_context apply_ctx(*this, _db, trx, message, code);
    apply_message(apply_ctx);
 
    // process_message recurses for each notified account, but we only want to run this check at the top level
    if (code == message.code && (_skip_flags & skip_authority_check) == false)
       EOS_ASSERT(apply_ctx.all_authorizations_used(), tx_irrelevant_auth,
-                 "Message declared an authority it did not need", ("message", message));
+                 "Message declared authorities it did not need: ${unused}",
+                 ("unused", apply_ctx.unused_authorizations())("message", message));
 
    output.notify.reserve( apply_ctx.notified.size() );
 

libraries/chain/include/eos/chain/message_handling_contexts.hpp

@@ -136,6 +136,7 @@ public:
    void require_recipient(const types::AccountName& account);
 
    bool all_authorizations_used() const;
+   vector<types::AccountPermission> unused_authorizations() const;
 
    const chain_controller&      controller;
    const chainbase::database&   db;  ///< database where state is stored

libraries/chain/message_handling_contexts.cpp

@@ -6,6 +6,9 @@
 
 #include <boost/algorithm/cxx11/all_of.hpp>
 #include <boost/range/algorithm/find_if.hpp>
+#include <boost/range/combine.hpp>
+#include <boost/range/adaptor/filtered.hpp>
+#include <boost/range/adaptor/transformed.hpp>
 
 namespace eos { namespace chain {
 
@@ -44,6 +47,19 @@ bool apply_context::all_authorizations_used() const {
    return boost::algorithm::all_of_equal(used_authorizations, true);
 }
 
+vector<types::AccountPermission> apply_context::unused_authorizations() const {
+   auto RemoveUsed = boost::adaptors::filtered([](const auto& tuple) {
+      return !boost::get<0>(tuple);
+   });
+   auto ToPermission = boost::adaptors::transformed([](const auto& tuple) {
+      return boost::get<1>(tuple);
+   });
+
+   // zip the parallel arrays, filter out the used authorizations, and return just the permissions that are left
+   auto range = boost::combine(used_authorizations, msg.authorization) | RemoveUsed | ToPermission;
+   return {range.begin(), range.end()};
+}
+
 //
 // i64 functions
 //