nim compiler mistakes `!(a == b)` for `!a == b` and fails to compile

[Muratam]

Overriding equal function causes incorrect behaviour. Nim compiler translates !(a == b) into !a == b and fails to compile.

Example

type CSet {.importcpp: "std::set", header: "<set>".} [T] = object
proc cInitSet(T: typedesc): CSet[T] {.importcpp: "std::set<'*1>()", nodecl.}
proc insert[T](self: var CSet[T],x:T) {.importcpp: "#.insert(@)", nodecl.}
proc `==`[T](x,y:CSet[T]):bool{.importcpp: "#==#", nodecl.}
var (S1,S2) = (cInitSet(int),cInitSet(int))
S1.insert 1
if S1 == S2: echo "wrong"
else: echo "correct"

Current Output

Nim fails to compile and prints the following error.

Error: execution of an external compiler program 'clang++ -c  -w  -~/.choosenim/toolchains/nim-0.20.0/lib -I~/codes/nim/ -o ~/.cache/nim/t_d/t.nim.cpp.o ~/.cache/nim/t_d/t.nim.cpp' failed with exit code: 1

~/.cache/nim/t_d/t.nim.cpp:153:7: error: invalid argument type 'TY_89ajMAHL4D29bP2aGRstu1mQ' (aka 'set<long long>') to unary expression
                if (!S1_X5vbOHyI0SI13LVkxEIzEQ==S2_q2YrwwKwgOf4xdemDnRTYA) goto LA4_;
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Expected Output

correct

Possible Solution (not fundamental)

Change the definition of ==

before:

proc `==`[T](x,y:CSet[T]):bool{.importcpp: "#==#", nodecl.}

after:

proc equalRawImpl[T](x,y:CSet[T]):bool{.importcpp: "#==#", nodecl.}
proc `==`[T](x,y:CSet[T]):bool = not(not(x.equalRawImpl y))

But, it is not not not a fundamental solution .

By the way, if you don't override == function, it will print the wrong result (print wrong).

Additional Information

Raw C code (error:14th line):

N_LIB_PRIVATE N_NIMCALL(void, NimMainModule)(void) {
{
    tyTuple_WVskh7WUQHL0ugdByxngAw T1_;
    nimfr_("t", "/path/to/t.nim");
    nimln_(8, "/path/to/t.nim"); 
    T1_.Field0 = std::set<NI>();
    T1_.Field1 = std::set<NI>();
    S1_X5vbOHyI0SI13LVkxEIzEQ = T1_.Field0;
    S2_q2YrwwKwgOf4xdemDnRTYA = T1_.Field1;
    nimln_(9, "/path/to/t.nim"); 
    S1_X5vbOHyI0SI13LVkxEIzEQ.insert(((NI) 1));
    nimln_(10, "/path/to/t.nim"); 
    {
        if (!S1_X5vbOHyI0SI13LVkxEIzEQ==S2_q2YrwwKwgOf4xdemDnRTYA) goto LA4_;
{       echoBinSafe(TM_earX20ePV9cxitomwdUMS7g_2, 1);
}   }
    goto LA2_;
    LA4_: ;
    {
        nimln_(11, "/path/to/t.nim"); 
        echoBinSafe(TM_earX20ePV9cxitomwdUMS7g_4, 1);
    }
    LA2_: ;
    popFrame();
}
}

$ nim -v
Nim Compiler Version 0.20.0 [MacOSX: amd64]
Compiled at 2019-06-06
Copyright (c) 2006-2019 by Andreas Rumpf
git hash: e7471cebae2a404f3e4239f199f5a0c422484aac
active boot switches: -d:release

It was not working in the previous Nim releases too.

[Araq]

Instead use

proc `==`[T](x,y:CSet[T]):bool{.importcpp: "(#==#)", nodecl.}

[andreaferretti]

Isn't this a duplicate of https://github.com/nim-lang/Nim/issues/2534 ?

[Araq]

Indeed.