1.99 beta crater regression: overflow evaluating the requirement

[theemathas]

This regression was found by the 1.99 crater run.

[INFO] [stdout] error[E0275]: overflow evaluating the requirement `matrix::Matrix<matrix::Matrix<_, _, _>, _, _>: core::ops::Add<matrix::Matrix<_, _, _>>`
[INFO] [stdout]    --> src/matrix.rs:347:26
[INFO] [stdout]     |
[INFO] [stdout] 347 |         let mut result = Matrix::new();
[INFO] [stdout]     |                          ^^^^^^^^^^^^^
[INFO] [stdout]     |
[INFO] [stdout]     = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`matrs`)
[INFO] [stdout] note: required for `matrix::Matrix<matrix::Matrix<matrix::Matrix<_, _, _>, _, _>, _, _>` to implement `core::ops::Add<matrix::Matrix<matrix::Matrix<_, _, _>, _, _>>`
[INFO] [stdout]    --> src/matrix.rs:216:7
[INFO] [stdout]     |
[INFO] [stdout] 212 |         T: CompliantNumerical + Add<TOther, Output = T>,
[INFO] [stdout]     |                                             ---------- unsatisfied trait bound introduced here
[INFO] [stdout] ...
[INFO] [stdout] 216 |     > Add<Matrix<TOther, ROWS, COLS>> for Matrix<T, ROWS, COLS>
[INFO] [stdout]     |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]     = note: 126 redundant requirements hidden
[INFO] [stdout]     = note: required for `Matrix<Matrix<Matrix<Matrix<_, _, _>, _, _>, _, _>, _, _>` to implement `Add<Matrix<Matrix<Matrix<Matrix<_, _, _>, _, _>, _, _>, _, _>>`
[INFO] [stdout] note: required by a bound in `MatrixInterface::new`
[INFO] [stdout]    --> src/traits.rs:85:5
[INFO] [stdout]     |
[INFO] [stdout]  85 |     Add<T>
[INFO] [stdout]     |     ^^^^^^ required by this bound in `MatrixInterface::new`
[INFO] [stdout] ...
[INFO] [stdout]  96 |     fn new() -> Self;
[INFO] [stdout]     |        --- required by a bound in this associated function
[INFO] [stdout]     = note: the full name for the type has been written to '/opt/rustwide/target/debug/deps/matrs-ff379938da94556c.long-type-4903951877788026595.txt'
[INFO] [stdout]     = note: consider using `--verbose` to print the full type name to the console
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error[E0275]: overflow evaluating the requirement `matrix::Matrix<matrix::Matrix<_, _, _>, _, _>: core::ops::Add<matrix::Matrix<_, _, _>>`
[INFO] [stdout]    --> src/lib.rs:74:26
[INFO] [stdout]     |
[INFO] [stdout]  74 |         let mut result = Matrix::new();
[INFO] [stdout]     |                          ^^^^^^^^^^^^^
[INFO] [stdout]     |
[INFO] [stdout]     = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`matrs`)
[INFO] [stdout] note: required for `matrix::Matrix<matrix::Matrix<matrix::Matrix<_, _, _>, _, _>, _, _>` to implement `core::ops::Add<matrix::Matrix<matrix::Matrix<_, _, _>, _, _>>`
[INFO] [stdout]    --> src/matrix.rs:216:7
[INFO] [stdout]     |
[INFO] [stdout] 212 |         T: CompliantNumerical + Add<TOther, Output = T>,
[INFO] [stdout]     |                                             ---------- unsatisfied trait bound introduced here
[INFO] [stdout] ...
[INFO] [stdout] 216 |     > Add<Matrix<TOther, ROWS, COLS>> for Matrix<T, ROWS, COLS>
[INFO] [stdout]     |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]     = note: 126 redundant requirements hidden
[INFO] [stdout]     = note: required for `Matrix<Matrix<Matrix<Matrix<_, _, _>, _, _>, _, _>, _, _>` to implement `Add<Matrix<Matrix<Matrix<Matrix<_, _, _>, _, _>, _, _>, _, _>>`
[INFO] [stdout] note: required by a bound in `MatrixInterface::new`
[INFO] [stdout]    --> src/traits.rs:85:5
[INFO] [stdout]     |
[INFO] [stdout]  85 |     Add<T>
[INFO] [stdout]     |     ^^^^^^ required by this bound in `MatrixInterface::new`
[INFO] [stdout] ...
[INFO] [stdout]  96 |     fn new() -> Self;
[INFO] [stdout]     |        --- required by a bound in this associated function
[INFO] [stdout]     = note: the full name for the type has been written to '/opt/rustwide/target/debug/deps/matrs-ff379938da94556c.long-type-862771533300215836.txt'
[INFO] [stdout]     = note: consider using `--verbose` to print the full type name to the console
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] For more information about this error, try `rustc --explain E0275`.

https://crater-reports.s3.amazonaws.com/beta-1.99-4/1.99.0-beta.1/gh/ivario123.matrix_math/log.txt

[theemathas]

Bisection result:

searched toolchains 96eb6d756bb98a82ae056c384575ff059bf80e8f through 0844f35a32c98882d77e39da8c2a872ec74615cd


********************************************************************************
Regression in 3d6c19bb9ab4798ecfb2ee943df01a811720fc27
********************************************************************************

Attempting to search unrolled perf builds
ERROR: couldn't find perf build comment

Regressed in #158436. cc @jdonszelmann (author), @lcnr (reviewer)

[theemathas]

Adding #![recursion_limit = "2048"] to the repo doesn't fix the issue, and #![recursion_limit = "4096"] causes the compiler to stack overflow, which suggests infinite recursion.

[cyrgani]

reduction:

pub trait Add<Rhs = Self> {
    type Output;
}
pub struct Matrix<T>(T);

impl<T> MatrixInterface<T> for Matrix<T> {
    fn new() -> Matrix<T> {
        loop {}
    }
}

impl<T: CompliantNumerical + Add<TOther, Output = T>, TOther> Add<Matrix<TOther>> for Matrix<T> {
    type Output = Matrix<T>;
}
impl<T> Add<T> for Matrix<T> {
    type Output = Matrix<T>;
}

pub fn to_matrix() -> Matrix<u64> {
    Matrix::new()
}

trait CompliantNumerical {}

impl CompliantNumerical for u64 {}

trait MatrixInterface<T>: Add<T> {
    fn new() -> Self;
}