Add support for nested tuples

[Y-Nak]

What is wrong?

contract Foo:
    def foo():
        x: (u256, (u256, u256)) = (0, (1, 2))

causes thread 'main' panicked at 'not yet implemented', compiler/src/lowering/names.rs:38:32

Backtrace

thread 'main' panicked at 'not yet implemented', compiler/src/lowering/names.rs:38:32
stack backtrace:
   0: rust_begin_unwind
             at /rustc/9bc8c42bb2f19e745a63f3445f1ac248fb015e53/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/9bc8c42bb2f19e745a63f3445f1ac248fb015e53/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/9bc8c42bb2f19e745a63f3445f1ac248fb015e53/library/core/src/panicking.rs:50:5
   3: fe_compiler::lowering::names::fixed_size_type_desc
             at ./compiler/src/lowering/names.rs:38:32
   4: fe_compiler::lowering::mappers::module::tuple_to_struct_def::{{closure}}
             at ./compiler/src/lowering/mappers/module.rs:43:62
   5: core::iter::adapters::map::map_fold::{{closure}}
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/adapters/map.rs:82:28
   6: <core::iter::adapters::enumerate::Enumerate<I> as core::iter::traits::iterator::Iterator>::fold::enumerate::{{closure}}
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/adapters/enumerate.rs:104:27
   7: core::iter::traits::iterator::Iterator::fold
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:2123:21
   8: <core::iter::adapters::enumerate::Enumerate<I> as core::iter::traits::iterator::Iterator>::fold
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/adapters/enumerate.rs:110:9
   9: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::fold
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/adapters/map.rs:122:9
  10: core::iter::traits::iterator::Iterator::for_each
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:775:9
  11: <alloc::vec::Vec<T,A> as alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/spec_extend.rs:42:17
  12: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/spec_from_iter_nested.rs:53:9
  13: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/spec_from_iter.rs:36:9
  14: <alloc::vec::Vec<T> as core::iter::traits::collect::FromIterator<T>>::from_iter
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:2401:9
  15: core::iter::traits::iterator::Iterator::collect
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:1764:9
  16: fe_compiler::lowering::mappers::module::tuple_to_struct_def
             at ./compiler/src/lowering/mappers/module.rs:37:18
  17: fe_compiler::lowering::mappers::module::module::{{closure}}
             at ./compiler/src/lowering/mappers/module.rs:28:32
  18: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:280:13
  19: core::option::Option<T>::map
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:487:29
  20: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::next
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/adapters/map.rs:101:9
  21: alloc::vec::Vec<T,A>::extend_desugared
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:2496:35
  22: <alloc::vec::Vec<T,A> as alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/spec_extend.rs:18:9
  23: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/spec_from_iter_nested.rs:37:9
  24: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/spec_from_iter.rs:36:9
  25: <alloc::vec::Vec<T> as core::iter::traits::collect::FromIterator<T>>::from_iter
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:2401:9
  26: core::iter::traits::iterator::Iterator::collect
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:1764:9
  27: fe_compiler::lowering::mappers::module::module
             at ./compiler/src/lowering/mappers/module.rs:25:35
  28: fe_compiler::lowering::lower
             at ./compiler/src/lowering/mod.rs:12:5
  29: fe_compiler::compile
             at ./compiler/src/lib.rs:51:29
  30: fe::main
             at ./src/main.rs:179:33
  31: core::ops::function::FnOnce::call_once
             at /home/y_nak/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

You've hit an internal compiler error. This is a bug in the Fe compiler.
Fe is still under heavy development, and isn't yet ready for production use.

How can it be fixed

Lower tuples recursively.

[mjobuda]

could replicate this.
I did some experiments in lowering/names.rs.
The crash was in

pub fn fixed_size_type_desc(typ: &FixedSize) -> fe::TypeDesc {
    match typ {
...
...
FixedSize::Tuple(_) => todo!()

While not fully understanding Rust nor the way this compiler works but I implemented it somehow.
Now the behaviour is that nested Tuple like
x: (u256,(u256, u256)) = (0,(0,0))
crashes with an AnalyzerError ...

"tuple_u256_tuple_u256_u256 expects 1 argument, but 2 were provided"`

So this is what the lowering generated with my changes. I don't know whether this is the supposed result that the lowering should generate.
Maybe somebody with a better understanding of the supposed Fe compiler functionality can answer this.
The next nested tuple i tried is:
x: (u256,(u256, u256),(u256, u256)) = (0,(0,0),(0,0))
This crashed with:
"tuple_u256_tuple_u256_u256_tuple_u256_u256 expects 1 argument, but 3 were provided"`
Is this the right way Tuples are to be represented for YUL?

My implementaion of FixedSize::Tuple(_) => todo!()

:

FixedSize::Tuple(tuple) => fe::TypeDesc::Tuple {
            items: {
                let mut v1: Vec1<Node<fe::TypeDesc>> =
                    Vec1::new(fixed_size_type_desc(tuple.items.first()).into_node());
                for item in tuple.items.iter().skip(1) {
                    v1.push(fixed_size_type_desc(&item).into_node())
                }
                Vec1::from(v1)
            },

The full Backtraces of the mentioned nested Tuples:

(base) mmm@ttt:~/fe$ ./target/debug/fe --overwrite ./tests/fixtures/features/nested_tuple.fe 
thread 'main' panicked at 'failed to analyze lowered AST: AnalyzerError([Diagnostic { severity: Error, code: None, message: "feature not yet implemented", labels: [Label { style: Primary, file_id: SourceFileId(333005103741714625151580942366672813312), range: 0..0, message: "non-base type struct fields is not yet implemented" }], notes: [] }, Diagnostic { severity: Error, code: None, message: "`tuple_u256_tuple_u256_u256` expects 1 argument, but 2 were provided", labels: [Label { style: Primary, file_id: SourceFileId(333005103741714625151580942366672813312), range: 62..71, message: "expects 1 argument" }, Label { style: Secondary, file_id: SourceFileId(333005103741714625151580942366672813312), range: 63..64, message: "" }, Label { style: Secondary, file_id: SourceFileId(333005103741714625151580942366672813312), range: 65..70, message: "supplied 2 arguments" }], notes: [] }])', compiler/src/lib.rs:55:59
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

You've hit an internal compiler error. This is a bug in the Fe compiler.
Fe is still under heavy development, and isn't yet ready for production use.

If you would, please report this bug at the following URL:
  https://github.com/ethereum/fe/issues/new
(base) mmm@ttt:~/fe$ ./target/debug/fe --overwrite ./tests/fixtures/features/nested_tuple.fe 
thread 'main' panicked at 'failed to analyze lowered AST: AnalyzerError([Diagnostic { severity: Error, code: None, message: "feature not yet implemented", labels: [Label { style: Primary, file_id: SourceFileId(194361644908539828904080200297581464859), range: 0..0, message: "non-base type struct fields is not yet implemented" }], notes: [] }, Diagnostic { severity: Error, code: None, message: "feature not yet implemented", labels: [Label { style: Primary, file_id: SourceFileId(194361644908539828904080200297581464859), range: 0..0, message: "non-base type struct fields is not yet implemented" }], notes: [] }, Diagnostic { severity: Error, code: None, message: "`tuple_u256_tuple_u256_u256_tuple_u256_u256` expects 1 argument, but 3 were provided", labels: [Label { style: Primary, file_id: SourceFileId(194361644908539828904080200297581464859), range: 75..90, message: "expects 1 argument" }, Label { style: Secondary, file_id: SourceFileId(194361644908539828904080200297581464859), range: 76..77, message: "" }, Label { style: Secondary, file_id: SourceFileId(194361644908539828904080200297581464859), range: 78..83, message: "" }, Label { style: Secondary, file_id: SourceFileId(194361644908539828904080200297581464859), range: 84..89, message: "supplied 3 arguments" }], notes: [] }])', compiler/src/lib.rs:55:59
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

You've hit an internal compiler error. This is a bug in the Fe compiler.
Fe is still under heavy development, and isn't yet ready for production use.

If you would, please report this bug at the following URL:
  https://github.com/ethereum/fe/issues/new

[sbillig]

Hey @mjobuda, sorry, I didn't notice you were looking into this. I implemented the lowering part of this in #459, because I was doing some nearby tuple-related refactoring, and I couldn't help myself. The resulting lowered code still won't compile, because it has nested structs which aren't supported yet (which maybe you're already working on in #465 🤘)

Eg (u8, (u16, u32)) becomes

struct tuple_u16_u32_:
  item0: u16
  item1: u32

struct tuple_u8_tuple_u16_u32__:
  item0: u8
  item1: tuple_u16_u32_

[mjobuda]

@sbillig exactly, in order to have nested tuples, nested structs must work(that's how I understand it after I implemented the strings in the struct fileds as part of #465 ).
Did I understand it right that in #459 you have implemented the lowering of the left side of expressions like:
x: (u16,(u8, u256)) = (1,(2,3))
?
And what is missing to get nested tuples to work is lowering the right side and getting the nested structs to work?

[Y-Nak]

Resolved in #459 and #642