Implement setmaxsupply

ref: eosnetworkfoundation/eos-system-contracts#125

contracts/eosio.token/include/eosio.token/eosio.token.hpp

@@ -60,6 +60,15 @@ namespace eosio {
          [[eosio::action]]
          void issuefixed( const name& to, const asset& supply, const string& memo );
 
+         /**
+          * Set the maximum supply of the token.
+          *
+          * @param issuer - the issuer account setting the maximum supply.
+          * @param maximum_supply - the maximum supply of the token.
+          */
+         [[eosio::action]]
+         void setmaxsupply( const name& issuer, const asset& maximum_supply );
+
          /**
           * The opposite for create action, if all validations succeed,
           * it debits the statstable.supply amount.

contracts/eosio.token/ricardian/eosio.token.contracts.md.in

@@ -28,6 +28,19 @@ This action will not result any any tokens being issued into circulation.
 
 RAM will deducted from {{$action.account}}’s resources to create the necessary records.
 
+<h1 class="contract">setmaxsupply</h1>
+
+---
+spec_version: "0.2.0"
+title: Set Max Supply
+summary: 'Set max supply for token'
+icon: @ICON_BASE_URL@/@TOKEN_ICON_URI@
+---
+
+{{issuer}} will be allowed to issue tokens into circulation, up to a maximum supply of {{maximum_supply}}.
+
+This action will not result any any tokens being issued into circulation.
+
 <h1 class="contract">issue</h1>
 
 ---

contracts/eosio.token/src/eosio.token.cpp

@@ -56,6 +56,25 @@ void token::issuefixed( const name& to, const asset& supply, const string& memo
    issue( to, quantity, memo );
 }
 
+void token::setmaxsupply( const name& issuer, const asset& maximum_supply )
+{
+   auto sym = maximum_supply.symbol;
+   check( maximum_supply.is_valid(), "invalid supply");
+   check( maximum_supply.amount > 0, "max-supply must be positive");
+
+   stats statstable( get_self(), sym.code().raw() );
+   auto & st = statstable.get( sym.code().raw(), "token supply does not exist" );
+   check( issuer == st.issuer, "only issuer can set token maximum supply" );
+   require_auth( st.issuer );
+
+   check( maximum_supply.symbol == st.supply.symbol, "symbol precision mismatch" );
+   check( maximum_supply.amount >= st.supply.amount, "max supply is less than available supply");
+
+   statstable.modify( st, same_payer, [&]( auto& s ) {
+      s.max_supply = maximum_supply;
+   });
+}
+
 void token::retire( const asset& quantity, const string& memo )
 {
     auto sym = quantity.symbol;

tests/eosio.token_tests.cpp

@@ -78,14 +78,21 @@ class eosio_token_tester : public tester {
       );
    }
 
-   action_result issuefixed( account_name issuer, asset supply, string memo ) {
-      return push_action( issuer, "issuefixed"_n, mvo()
-           ( "to", issuer)
+   action_result issuefixed( account_name to, asset supply, string memo ) {
+      return push_action( to, "issuefixed"_n, mvo()
+           ( "to", to)
            ( "supply", supply)
            ( "memo", memo)
       );
    }
 
+   action_result setmaxsupply( account_name issuer, asset maximum_supply ) {
+      return push_action( issuer, "setmaxsupply"_n, mvo()
+           ( "issuer", issuer)
+           ( "maximum_supply", maximum_supply)
+      );
+   }
+
    action_result retire( account_name issuer, asset quantity, string memo ) {
       return push_action( issuer, "retire"_n, mvo()
            ( "quantity", quantity)
@@ -270,6 +277,42 @@ BOOST_FIXTURE_TEST_CASE( issuefixed_tests, eosio_token_tester ) try {
 
 } FC_LOG_AND_RETHROW()
 
+BOOST_FIXTURE_TEST_CASE( setmaxsupply_tests, eosio_token_tester ) try {
+
+   auto token = create( "alice"_n, asset::from_string("1000.000 TKN"));
+   produce_blocks(1);
+
+   issue( "alice"_n, asset::from_string("1000.000 TKN"), "issue active supply" );
+
+   BOOST_REQUIRE_EQUAL( wasm_assert_msg( "quantity exceeds available supply" ),
+                        issue( "alice"_n, asset::from_string("1000.000 TKN"), "quantity exceeds available supply" )
+   );
+
+   setmaxsupply( "alice"_n, asset::from_string("2000.000 TKN") );
+
+   issue( "alice"_n, asset::from_string("1000.000 TKN"), "issue active supply" );
+
+   auto stats = get_stats("3,TKN");
+   // REQUIRE_MATCHING_OBJECT( stats, mvo()
+   //    ("supply", "2000.000 TKN")
+   //    ("max_supply", "2000.000 TKN")
+   //    ("issuer", "alice")
+   // );
+
+   BOOST_REQUIRE_EQUAL( wasm_assert_msg( "symbol precision mismatch" ),
+                        setmaxsupply( "alice"_n, asset::from_string("3000 TKN") )
+   );
+
+   BOOST_REQUIRE_EQUAL( wasm_assert_msg( "only issuer can set token maximum supply" ),
+                        setmaxsupply( "bob"_n, asset::from_string("1000.000 TKN") )
+   );
+
+   BOOST_REQUIRE_EQUAL( wasm_assert_msg( "max supply is less than available supply" ),
+                        setmaxsupply( "alice"_n, asset::from_string("1000.000 TKN") )
+   );
+
+} FC_LOG_AND_RETHROW()
+
 BOOST_FIXTURE_TEST_CASE( retire_tests, eosio_token_tester ) try {
 
    auto token = create( "alice"_n, asset::from_string("1000.000 TKN"));