LLVM stacktrace when running generic code with interfaces

[FelipeLopes]

Description of the bug:

When running some code making use of generics and interfaces, explorer fails with a stack trace ending with

CHECK failure at explorer/interpreter/interpreter.cpp:281: v->kind() == Value::Kind::LValue

What did you do, or what's a simple way to reproduce the bug?

On commit 5709014, add a file hello.carbon with the following content:

package Hello api;

class Rng {
    fn Create(seed: i32) -> Self {
        return {.seed = seed};
    }
    fn NextInt[addr me: Self*]() -> i32 {
        let a: i32 = (8121*(*me).seed + 28411) & 32767;
        (*me).seed = a;
        return a;
    }
    var seed: i32;
}

interface Roller {
    fn This[me: Self]() -> Self;
    fn RollNumber[addr me: Self*]() -> i32;
}

class DiceRoller {
    fn Create(seed: i32, sides: i32) -> Self {
        return {.rng = Rng.Create(seed), .sides = sides};
    }
    impl DiceRoller as Roller {
        fn This[me: Self]() -> Self {
            return me;
        }
        fn RollNumber[addr me: Self*]() -> i32 {
            return (*me).rng.NextInt()%((*me).sides);
        }
    }
    var rng: Rng;
    var sides: i32;
}

class SerialRoller {
    fn Create(total: i32) -> Self {
        return {.current = 0, .total = total};
    }
    impl SerialRoller as Roller {
        fn This[me: Self]() -> Self {
            return me;
        }
        fn RollNumber[addr me: Self*]() -> i32 {
            let ans: i32 = (*me).current;
            (*me).current = (*me).current + 1;
            if ((*me).current == (*me).total) {
                (*me).current = 0;
            }
            return ans;
        }
    }
    var current: i32;
    var total: i32;
}

interface Mapper {
    fn This[me: Self]() -> Self;
    fn MapString[me: Self](i: i32) -> String;
}

class NameMapper {
    fn Create(arr: [String; 6]) -> Self {
        return {.arr = arr};
    }
    impl NameMapper as Mapper {
        fn This[me: Self]() -> Self {
            return me;
        }
        fn MapString[me: Self](i: i32) -> String {
            return me.arr[i];
        }
    }
    var arr: [String; 6];
}

class ParityMapper {
    fn Create(param: i32) -> Self {
        return {.param = param};
    }
    impl ParityMapper as Mapper {
        fn This[me: Self]() -> Self {
            return me;
        }
        fn MapString[me: Self](i: i32) -> String {
            let x: i32 = me.param*me.param + i;
            if (x % 2 == 0) {
                return "even";
            } else {
                return "odd";
            }
        }
    }
    var param: i32;
}

class StringRoller(R:! Roller, M:! Mapper) {
    fn Create(roller: R, mapper: M) -> Self {
        return {.roller = roller.This(), .mapper = mapper.This()};
    }
    fn RollString[me: Self]() -> String {
        return me.mapper.MapString(me.roller.RollNumber());
    }
    var roller: R;
    var mapper: M;
}

fn Main() -> i32 {
    var diceRoller: DiceRoller = DiceRoller.Create(314, 6);
    var nameMapper: NameMapper = NameMapper.Create(
        ("one", "two", "three", "four", "five", "six")
    );
    var nameRoller: StringRoller(DiceRoller, NameMapper) =
        StringRoller(DiceRoller, NameMapper).Create(diceRoller, nameMapper);
    var i: i32 = 0;
    while (i < 30) {
        Print(nameRoller.RollString());
        i = i + 1;
    }
    var parityMapper: ParityMapper = ParityMapper.Create(0);
    var serialRoller: SerialRoller = SerialRoller.Create(5);
    return 0;
}

and run it with bazel run //explorer -- hello.carbon

What did you expect to happen?

I expected it to print an output or report a failed compilation.

What actually happened?

The following error is displayed:

Stack trace:
 #0 0x0000556883bf506b backtrace (/root/.cache/bazel/_bazel_root/924e82cb53c08cf8a432318b2f0f4261/execroot/carbon/bazel-out/k8-fastbuild/bin/explorer/explorer+0x52306b)
 #1 0x0000556883fda54d llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /proc/self/cwd/external/llvm-project/llvm/lib/Support/Unix/Signals.inc:569:13
 #2 0x0000556883c83451 Carbon::Internal::ExitingStream::ExitingStream() /proc/self/cwd/./common/check_internal.h:35:3
 #3 0x0000556883dd247a Carbon::PatternMatch(Carbon::Value const*, Carbon::Value const*, Carbon::SourceLocation, std::__1::optional<Carbon::RuntimeScope*>, std::__1::map<Carbon::GenericBinding const*, Carbon::Value const*, std::__1::less<Carbon::GenericBinding const*>, std::__1::allocator<std::__1::pair<Carbon::GenericBinding const* const, Carbon::Value const*>>>&, std::__1::optional<llvm::raw_ostream*>, Carbon::Arena*) /proc/self/cwd/explorer/interpreter/interpreter.cpp:281:7
 #4 0x0000556883de937a Carbon::Interpreter::CallFunction(Carbon::CallExpression const&, Carbon::Value const*, Carbon::Value const*, std::__1::map<Carbon::ImplBinding const*, Carbon::Value const*, std::__1::less<Carbon::ImplBinding const*>, std::__1::allocator<std::__1::pair<Carbon::ImplBinding const* const, Carbon::Value const*>>>&&) /proc/self/cwd/explorer/interpreter/interpreter.cpp:903:7
 #5 0x0000556883df17c9 Carbon::Interpreter::StepExp() /proc/self/cwd/explorer/interpreter/interpreter.cpp:1246:7
 #6 0x0000556883de0028 index /usr/lib/llvm-15/bin/../include/c++/v1/variant:797:12
 #7 0x0000556883de0028 index /usr/lib/llvm-15/bin/../include/c++/v1/variant:1450:59
 #8 0x0000556883de0028 __holds_alternative<1UL, Carbon::Error, Carbon::Success> /usr/lib/llvm-15/bin/../include/c++/v1/variant:1476:14
 #9 0x0000556883de0028 holds_alternative<Carbon::Success, Carbon::Error, Carbon::Success> /usr/lib/llvm-15/bin/../include/c++/v1/variant:1482:10
#10 0x0000556883de0028 ok /proc/self/cwd/./common/error.h:80:36
#11 0x0000556883de0028 Carbon::Interpreter::Step() /proc/self/cwd/explorer/interpreter/interpreter.cpp:2055:7
#12 0x0000556883e12a4f index /usr/lib/llvm-15/bin/../include/c++/v1/variant:797:12
#13 0x0000556883e12a4f index /usr/lib/llvm-15/bin/../include/c++/v1/variant:1450:59
#14 0x0000556883e12a4f __holds_alternative<1UL, Carbon::Error, Carbon::Success> /usr/lib/llvm-15/bin/../include/c++/v1/variant:1476:14
#15 0x0000556883e12a4f holds_alternative<Carbon::Success, Carbon::Error, Carbon::Success> /usr/lib/llvm-15/bin/../include/c++/v1/variant:1482:10
#16 0x0000556883e12a4f ok /proc/self/cwd/./common/error.h:80:36
#17 0x0000556883e12a4f Carbon::Interpreter::RunAllSteps(std::__1::unique_ptr<Carbon::Action, std::__1::default_delete<Carbon::Action>>) /proc/self/cwd/explorer/interpreter/interpreter.cpp:2087:5
#18 0x0000556883e1398a reset /usr/lib/llvm-15/bin/../include/c++/v1/__memory/unique_ptr.h:302:28
#19 0x0000556883e1398a ~unique_ptr /usr/lib/llvm-15/bin/../include/c++/v1/__memory/unique_ptr.h:259:19
#20 0x0000556883e1398a Carbon::InterpProgram(Carbon::AST const&, Carbon::Arena*, std::__1::optional<llvm::raw_ostream*>) /proc/self/cwd/explorer/interpreter/interpreter.cpp:2112:3
#21 0x0000556883c86dd2 Carbon::ExecProgram(Carbon::Arena*, Carbon::AST, std::__1::optional<llvm::raw_ostream*>) /proc/self/cwd/explorer/interpreter/exec_program.cpp:67:3
#22 0x0000556883c7b503 Carbon::ExplorerMain(int, char**, void*, llvm::StringRef) /proc/self/cwd/explorer/main.cpp:108:34
#23 0x0000556883c79af7 main /proc/self/cwd/explorer/main_bin.cpp:12:3
#24 0x00007f7cd45b0d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#25 0x00007f7cd45b0e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#26 0x0000556883bb7885 _start (/root/.cache/bazel/_bazel_root/924e82cb53c08cf8a432318b2f0f4261/execroot/carbon/bazel-out/k8-fastbuild/bin/explorer/explorer+0x4e5885)
CHECK failure at explorer/interpreter/interpreter.cpp:281: v->kind() == Value::Kind::LValue

Any other information, logs, or outputs that you want to share?

No response

[zygoloid]

I believe the issue here is that addr me: Self* does not currently work for interface methods, only for class methods.

[zygoloid]

Confirmed this is a duplicate of #2223.