Build failed on rust 1.47

[enfipy]

Currently, it's not possible to build substrate on newest rust version due to the next error:

     Compiling sp-arithmetic v2.0.0-rc6 (https://github.com/paritytech/substrate.git?tag=v2.0.0-rc6#be8bb186)
  error[E0282]: type annotations needed
      --> /home/runner/.cargo/git/checkouts/substrate-7e08433d4c370a21/be8bb18/primitives/arithmetic/src/fixed_point.rs:541:9
       |
  541  |                   let accuracy = P::ACCURACY.saturated_into();
       |                       ^^^^^^^^ consider giving `accuracy` a type
  ...
  1595 | / implement_fixed!(
  1596 | |     FixedI64,
  1597 | |     test_fixed_i64,
  1598 | |     i64,
  ...    |
  1601 | |     "_Fixed Point 64 bits signed, range = [-9223372036.854775808, 9223372036.854775807]_",
  1602 | | );
       | |__- in this macro invocation
       |
       = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

  error[E0282]: type annotations needed
      --> /home/runner/.cargo/git/checkouts/substrate-7e08433d4c370a21/be8bb18/primitives/arithmetic/src/fixed_point.rs:541:9
       |
  541  |                   let accuracy = P::ACCURACY.saturated_into();
       |                       ^^^^^^^^ consider giving `accuracy` a type
  ...
  1604 | / implement_fixed!(
  1605 | |     FixedI128,
  1606 | |     test_fixed_i128,
  1607 | |     i128,
  ...    |
  1611 | |         [-170141183460469231731.687303715884105728, 170141183460469231731.687303715884105727]_",
  1612 | | );
       | |__- in this macro invocation
       |
       = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

  error[E0282]: type annotations needed
      --> /home/runner/.cargo/git/checkouts/substrate-7e08433d4c370a21/be8bb18/primitives/arithmetic/src/fixed_point.rs:541:9
       |
  541  |                   let accuracy = P::ACCURACY.saturated_into();
       |                       ^^^^^^^^ consider giving `accuracy` a type
  ...
  1614 | / implement_fixed!(
  1615 | |     FixedU128,
  1616 | |     test_fixed_u128,
  1617 | |     u128,
  ...    |
  1621 | |         [0.000000000000000000, 340282366920938463463.374607431768211455]_",
  1622 | | );
       | |__- in this macro invocation
       |
       = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

  error: aborting due to 3 previous errors

  For more information about this error, try `rustc --explain E0282`.
  error: could not compile `sp-arithmetic`

  To learn more, run the command again with --verbose.
  warning: build failed, waiting for other jobs to finish...
  error: build failed
warning: build failed, waiting for other jobs to finish...
error: build failed
Error: Process completed with exit code 101.

The error persists in substrate v2.0 too.

[bkchr]

Please use the search.

It is failing because latest nightly is broken: rust-lang/rust#77653

Please downgrade your nightly.