feat!: TXE single execution env

[Thunkar]

TXE single execution env

Previously, TXE had a weird dual model in which direct calls from test code would "inline" contract code and call it directly. This was very fast, but unfortunately wasn't possible when doing an external call.

test -> env.call(ContractUnderTest.fn) (inlined call) -> ExternalContract::at(addr).fn (nested call inside ACVM or AVM simulator)

This forced us to reproduce the simulator behavior both in Noir and in TXE, leading to bugs and generally terrible UX. The upside is that besides being faster, it also allowed the developer to NOT recompile the contract code on every change, only when modifying external contracts that were called from the one under test.

Fortunately, recent Brillig improvements allow us to do every single call (including inside tests) as a nested call, which leads to a lot of deduplication and a more consistent UX. Contracts under test now have to always be recompiled and deployed, but it is a small price to pay for consistency's sake.

Public rethrows and proper support for #[test(should_fail_with="message")]

Previously, the very weird dual model introduced problems when trying to parse errors thrown by public functions, specially when they were nested calls. This is NO MORE and we can always use Noir's native system to parse error messages and ensure negative tests fail properly

Call interface rework

Since TXE has been simplified, call interfaces don't need the weird original: fn field that previously allowed use to call the "macrofied" version of the contract function inline with the test. However, this rework led to the discovery of an issue: return types from call interfaces were incorrectly typed, and were only bound by the compiler when used after the call. This has been fixed by adding a zeroed return_value field to the call interfaces (essentially rust's PhantomData) so we are able to properly type them and leverage the type system to ensure the values are not only what we expect, but of the type we expect.

[fcarreiro]

Lovely! I wouldn't be surprised if you could remove even more (e.g., isStaticCall)

[github-actions]

Changes to public function bytecode sizes

Generated at commit: 3135bd23e971903700b13b69ec24df74bbe29ebc, compared to commit: 1ce0fa58d14c6b9b5f26f3cd3bda3589dd85b4e5

🧾 Summary (100% most significant diffs)

Program	Bytecode size in bytes (+/-)	%
AvmTest::bulk_testing	+162 ❌	+0.68%
Lending::public_dispatch	-880 ✅	-3.47%
Lending::_withdraw	-308 ✅	-4.18%
Lending::_borrow	-308 ✅	-4.21%
Uniswap::public_dispatch	-1,175 ✅	-5.00%
Uniswap::swap_public	-1,782 ✅	-12.46%

---

Full diff report 👇

Program	Bytecode size in bytes (+/-)	%
AvmTest::bulk_testing	23,994 (+162)	+0.68%
Lending::public_dispatch	24,504 (-880)	-3.47%
Lending::_withdraw	7,069 (-308)	-4.18%
Lending::_borrow	7,013 (-308)	-4.21%
Uniswap::public_dispatch	22,331 (-1,175)	-5.00%
Uniswap::swap_public	12,515 (-1,782)	-12.46%

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[nventuro]

I don't understand this

[Thunkar]

Call interfaces were sort of broken before. Return value types were unbound and that led to weird situations such as:

#[private]
fn my_fn() -> u8 {...}

...

#[test]
fn test_my_fn() {
  let result = MyContract::at(somewhere).my_fn().call(&mut env.private());
  assert(result == 8 // this is a Field, so result is cast to Field);
}

return_value in the call interfaces is essentially rust's PhantomData, so we are able to properly type the return value of the call interface (both in TXE and actual contracts)

[nventuro]

I thought I understood this, and did some reading around on PhantomData, but then tried to write down a comment explaining why zeroed needs to be there and failed.

[Thunkar]

It's similar to when we needed array hints in methods for length...we need a return_type variable with the correct Type, but we don't know what the actual value is (because we haven't called the function yet)