Transaction id is a hash of what?

Question

https://eosio-cpp.readme.io/docs/communication-model states:

On completion of the transaction, a transaction receipt is generated. This receipt takes the form a hash.

The transaction receipt is a hash of what, exactly?

Answer 1

From what I can tell, it's a hash of the transaction itself and the chain id:

From libraries/chain/transaction.cpp:

digest_type transaction::sig_digest( const chain_id_type& chain_id, const vector<bytes>& cfd )const {
   digest_type::encoder enc;
   fc::raw::pack( enc, chain_id );
   fc::raw::pack( enc, *this );
   if( cfd.size() ) {
      fc::raw::pack( enc, digest_type::hash(cfd) );
   } else {
      fc::raw::pack( enc, digest_type() );
   }
   return enc.result();
}

where a transaction is defined as follows:

 struct transaction : public transaction_header {
      vector<action>         context_free_actions;
      vector<action>         actions;
      extensions_type        transaction_extensions;

      transaction_id_type        id()const;
      digest_type                sig_digest( const chain_id_type& chain_id, const vector<bytes>& cfd = vector<bytes>() )const;
      flat_set<public_key_type>  get_signature_keys( const vector<signature_type>& signatures,
                                                     const chain_id_type& chain_id,
                                                     const vector<bytes>& cfd = vector<bytes>(),
                                                     bool allow_duplicate_keys = false,
                                                     bool use_cache = true )const;

      uint32_t total_actions()const { return context_free_actions.size() + actions.size(); }
      account_name first_authorizor()const {
         for( const auto& a : actions ) {
            for( const auto& u : a.authorization )
               return u.actor;
         }
         return account_name();
      }

};