Avoid hash collisions in calldata creation

.gitignore

@@ -1,5 +1,5 @@
 .rebar3
-_*
+_[^_]*
 .eunit
 *.o
 *.beam

src/aeso_compiler.erl

@@ -188,7 +188,7 @@ check_call1(ContractString0, FunName, Args, Options) ->
             aevm ->
                 %% First check the contract without the __call function
                 #{} = string_to_icode(ContractString0, Options),
-        ContractString = insert_call_function(ContractString0, FunName, Args, Options),
+                ContractString = insert_call_function(ContractString0, ?CALL_NAME, FunName, Args, Options),
                 #{typed_ast := TypedAst,
                   icode     := Icode} = string_to_icode(ContractString, Options),
                 {ok, {FunName, {fun_t, _, _, ArgTypes, RetType}}} = get_call_type(TypedAst),
@@ -211,13 +211,13 @@ check_call1(ContractString0, FunName, Args, Options) ->
                 %% First check the contract without the __call function
                 #{fcode := OrgFcode} = string_to_fcode(ContractString0, Options),
                 FateCode = aeso_fcode_to_fate:compile(OrgFcode, []),
-                _SymbolHashes = maps:keys(aeb_fate_code:symbols(FateCode)),
-                %% TODO collect all hashes and compute the first name without hash collision to
-                %% be used as __callX
-                %% case aeb_fate_code:symbol_identifier(<<"__call">>) of
-                ContractString = insert_call_function(ContractString0, FunName, Args, Options),
+                %% collect all hashes and compute the first name without hash collision to
+                SymbolHashes = maps:keys(aeb_fate_code:symbols(FateCode)),
+                CallName = first_none_match(?CALL_NAME, SymbolHashes,
+                                            lists:seq($1, $9) ++ lists:seq($A, $Z) ++ lists:seq($a, $z)),
+                ContractString = insert_call_function(ContractString0, CallName, FunName, Args, Options),
                 #{fcode := Fcode} = string_to_fcode(ContractString, Options),
-                #{args := CallArgs} = maps:get({entrypoint, <<"__call">>}, maps:get(functions, Fcode)),
+                #{args := CallArgs} = maps:get({entrypoint, list_to_binary(CallName)}, maps:get(functions, Fcode)),
                 {ok, FunName, CallArgs}
         end
     catch
@@ -233,17 +233,26 @@ check_call1(ContractString0, FunName, Args, Options) ->
                                 fun (E) -> io_lib:format("~p", [E]) end)}
     end.
 
+first_none_match(CallName, Hashes, []) ->
+    error(unable_to_find_unique_call_name);
+first_none_match(CallName, Hashes, [Char|Chars]) ->
+    case not lists:member(aeb_fate_code:symbol_identifier(list_to_binary(CallName)), Hashes) of
+        true ->
+            CallName;
+        false ->
+            first_none_match(?CALL_NAME++[Char], Hashes, Chars)
+    end.
 
 %% Add the __call function to a contract.
--spec insert_call_function(string(), string(), [string()], options()) -> string().
-insert_call_function(Code, FunName, Args, Options) ->
+-spec insert_call_function(string(), string(), string(), [string()], options()) -> string().
+insert_call_function(Code, Call, FunName, Args, Options) ->
     Ast = parse(Code, Options),
     Ind = last_contract_indent(Ast),
     lists:flatten(
         [ Code,
           "\n\n",
           lists:duplicate(Ind, " "),
-          "stateful function __call() = ", FunName, "(", string:join(Args, ","), ")\n"
+          "stateful function ", Call,"() = ", FunName, "(", string:join(Args, ","), ")\n"
         ]).
 
 -spec insert_init_function(string(), options()) -> string().

test/contracts/__call.aes

@@ -0,0 +1,5 @@
+
+contract Identity =
+  function main (x:int) = x
+
+  function __call() = 12