Rustdoc with -Znormalize-docs fails to build docs for generic-array

[WaffleLapkin]

Building docs for generic-array with -Znormalize-docs fails since its git tag 0.0.3 with the following error (latest tag 1.0.0 also reproduces the same exact issue):

; RUSTDOCFLAGS="-Znormalize-docs" cargo +nightly doc
 Documenting typenum v1.17.0
 Documenting generic-array v0.0.3 (/home/waffle/projects/repos/generic-array)
error[E0275]: overflow evaluating the requirement `typenum::UInt<typenum::UInt<typenum::UInt<typenum::UInt<typenum::UInt<typenum::UInt<typenum::UInt<..., ...>, ...>, ...>, ...>, ...>, ...>, ...>: typenum::Unsigned`
  |
  = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`generic_array`)
  = note: required for `UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<..., ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>` to implement `std::ops::Shl<typenum::B1>`
  = note: the full type name has been written to 'generic_array.long-type-10849549341428477219.txt'
  = note: 121 redundant requirements hidden
  = note: required for `typenum::UInt<typenum::UInt<typenum::UTerm, typenum::B1>, typenum::B0>` to implement `std::ops::Shl<typenum::UInt<_, _>>`
  = note: required for `typenum::UTerm` to implement `typenum::uint::SetBit<typenum::UInt<_, _>, typenum::B1>`
  = note: required for `()` to implement `typenum::private::PrivateDivIf<typenum::UInt<Ul, Bl>, typenum::UInt<Ur, Br>, typenum::UTerm, _, typenum::UInt<_, _>, typenum::Equal>`

For more information about this error, try `rustc --explain E0275`.
error: could not document `generic-array`

Caused by:
  process didn't exit successfully: `/home/waffle/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustdoc --crate-type rlib --crate-type dylib --crate-name generic_array src/lib.rs -o /home/waffle/projects/repos/generic-array/target/doc --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=191 -C metadata=db8181fe6603c7bc -L dependency=/home/waffle/projects/repos/generic-array/target/debug/deps --extern typenum=/home/waffle/projects/repos/generic-array/target/debug/deps/libtypenum-1d6ab7b7d1feadca.rmeta -Znormalize-docs --crate-version 0.0.3` (exit status: 1)

notes on 0.0.2

On 0.0.2 rustdoc also fails, but with a slightly different error:

; RUSTDOCFLAGS="-Znormalize-docs" cargo +nightly doc
    Updating crates.io index
 Documenting typenum v0.1.1
error[E0275]: overflow evaluating the requirement `uint::UInt<uint::UInt<uint::UInt<uint::UInt<uint::UInt<uint::UInt<uint::UInt<..., ...>, ...>, ...>, ...>, ...>, ...>, ...>: uint::Unsigned`
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`typenum`)
note: required for `UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<UInt<..., ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>, ...>` to implement `std::ops::Shl<uint::UTerm>`
   --> /home/waffle/.cargo/registry/src/index.crates.io-6f17d22bba15001f/typenum-0.1.1/src/uint.rs:435:27
    |
435 | impl<U: Unsigned, B: Bit> Shl<UTerm> for UInt<U, B> {
    |         --------          ^^^^^^^^^^     ^^^^^^^^^^
    |         |
    |         unsatisfied trait bound introduced here
    = note: the full type name has been written to 'typenum.long-type-9142539435321689143.txt'
    = note: 126 redundant requirements hidden
    = note: required for `uint::UInt<uint::UInt<uint::UTerm, bit::B1>, bit::B0>` to implement `std::ops::Shl<uint::UInt<_, _>>`

For more information about this error, try `rustc --explain E0275`.
error: could not document `typenum`

Caused by:
  process didn't exit successfully: `/home/waffle/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustdoc --crate-type lib --crate-name typenum /home/waffle/.cargo/registry/src/index.crates.io-6f17d22bba15001f/typenum-0.1.1/src/lib.rs --cap-lints allow -o /home/waffle/projects/repos/generic-array/target/doc --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=191 -C metadata=1850fe6d6e4be91a -L dependency=/home/waffle/projects/repos/generic-array/target/debug/deps -Znormalize-docs --crate-version 0.1.1` (exit status: 1)

Why I consider this a rustdoc bug (as opposed to generic-array)

Mainly because the crate builds just fine with rustc, so it's only doc normalization that can't chew through it.

But also:

1. It seems weird to me that an error during type normalization for docs results in an error. I would expect it to just not normalize if it can't
2. It also fails if you compile a crate that depends on generic-array (potentially though a list of other deps), which is doubly annoying (I don't think there needs to be any public item of generic-array exported from a crate for the build to fail)

Discovery context

This was discovered a couple days ago when I noticed that I can't build docs for teloxide (2945f4d3) locally. As it turns out it was caused by update of sqlx (0.6 -> 0.7.3) in 4fcb906 which looks like it adds a dependency on generic-array (which is somewhat weird, considering that you can just use const generics now, I think?...).

Meta

rustdoc --version --verbose:

rustdoc 1.77.0-nightly (88189a71e 2024-01-19)
binary: rustdoc
commit-hash: 88189a71e4e4376eea82ac61db6a539612eb200a
commit-date: 2024-01-19
host: x86_64-unknown-linux-gnu
release: 1.77.0-nightly
LLVM version: 17.0.6

[WaffleLapkin]

Oh. I actually already reported this issue as #93703, which seems to have been closed as a dup of #81091...

[WaffleLapkin]

Looks like 4fcb906 just re-introduced a dependency on generic-array that was somehow removed before that. Welp.

I'm going to close this on the premise that it's indeed just #81091, although I'm not exactly sure.