nightly-2024-04-05 regression: error[E0275]: overflow evaluating the requirement

[stepancheg]

Code

Sorry, I don't have simple code to reproduce the issue, because the project is large.

The repro is this:

$ git clone https://github.com/facebook/starlark-rust

$ git co 96a2bf3d164d99cccc6cf330433d770e7d01b15a  # Latest revision

$ cargo +nightly-2024-04-05-aarch64-apple-darwin test -p starlark --lib --no-run

This works (warnings are unrelated)

$ cargo +nightly-2024-04-06-aarch64-apple-darwin test -p starlark --lib --no-run

...

error[E0275]: overflow evaluating the requirement `&_: StarlarkTypeRepr`
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`starlark`)
note: required for `&[_]` to implement `StarlarkTypeRepr`
   --> starlark/src/values/types/list/value.rs:251:17
    |
251 | impl<'a, V: 'a> StarlarkTypeRepr for &'a [V]
    |                 ^^^^^^^^^^^^^^^^     ^^^^^^^
252 | where
253 |     &'a V: StarlarkTypeRepr,
    |            ---------------- unsatisfied trait bound introduced here
    = note: 126 redundant requirements hidden
    = note: required for `&[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[...]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]` to implement `StarlarkTypeRepr`
    = note: the full name for the type has been written to '/Users/nga/devel/starlark-rust/target/debug/deps/starlark-e78de373a7652cbb.long-type-11371795697589288004.txt'

Contents of the mentioned file is:

&[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[_]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]

I tried increasing #![recursion_limit = "256"], did not help.

Version it worked on

$ cargo +nightly-2024-04-05-aarch64-apple-darwin --version
cargo 1.79.0-nightly (0637083df 2024-04-02)
$ rustc +nightly-2024-04-05-aarch64-apple-darwin --version
rustc 1.79.0-nightly (385fa9d84 2024-04-04)

Also works on stable.

Version with regression

$ cargo +nightly-2024-04-06-aarch64-apple-darwin --version
cargo 1.79.0-nightly (0637083df 2024-04-02)
$ rustc +nightly-2024-04-06-aarch64-apple-darwin --version
rustc 1.79.0-nightly (9d79cd5f7 2024-04-05)

This may be duplicate of #123493 because timing.

[SergioBenitez]

This is also affecting diesel:

error[E0275]: overflow evaluating the requirement `(&_, &_, &_, ..., ..., ...): diesel::Insertable<...>`
  |
  = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`rust_out`)
  = note: required for `&(_, _, _, _, _, _)` to implement `diesel::Insertable<table>`
  = note: 127 redundant requirements hidden
  = note: required for `(&((..., ..., ..., ..., ..., ...), ..., ..., ..., ..., ...), ..., ..., ..., ..., ...)` to implement `diesel::Insertable<table>`
  = note: the full name for the type has been written to '/tmp/rustdoctestmnF1pz/rust_out.long-type-2635572469679000095.txt'
  = note: consider using `--verbose` to print the full type name to the console

error: aborting due to 1 previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0275`.
Couldn't compile the test.

failures:
    contrib/db_pools/lib/src/diesel.rs - diesel (line 26)

[dtolnay]

Using the starlark-rust repro, this bisects to #122747. @Urgau @lcnr

[lcnr]

overflow is fatal in the old trait solver, so by proving additional goals, especially if they have inference variables, we can end up with new sources of overflow causing an error.

the most straightforward fix is to use the new solver for this lint 😁 given that the lint uses an empty environment it uses pretty much the same parts of the solver as coherence so it should already be ready for that

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-high