ICE running cargo doc with 1.56

[hdevalence]

Code

Running cargo doc --no-deps -p pkg1 -p pkg2 ... in our project workspace started failing with ICEs when we upgraded to Rust 1.56:

https://github.com/penumbra-zone/penumbra/runs/3986489751?check_suite_focus=true#step:8:408

Rolling back to Rust 1.55 works fine:

https://github.com/penumbra-zone/penumbra/actions/runs/1377223824

Error output

 Documenting penumbra v0.1.0 (/home/runner/work/penumbra/penumbra/penumbra)
thread 'rustc' panicked at 'index out of bounds: the len is 130 but the index is 130', compiler/rustc_metadata/src/creader.rs:146:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

error: Unrecognized option: 'crate-version'

error: could not document `penumbra`

Caused by:
  process didn't exit successfully: `rustdoc --edition=2018 --crate-type lib --crate-name penumbra penumbra/src/lib.rs -o /home/runner/work/penumbra/penumbra/target/doc --error-format=json --json=diagnostic-rendered-ansi -L dependency=/home/runner/work/penumbra/penumbra/target/debug/deps --extern anyhow=/home/runner/work/penumbra/penumbra/target/debug/deps/libanyhow-cde2a164ebc04e3b.rmeta --extern bytes=/home/runner/work/penumbra/penumbra/target/debug/deps/libbytes-1fc3a8241f0d7795.rmeta --extern futures=/home/runner/work/penumbra/penumbra/target/debug/deps/libfutures-3f39ac28cae99c47.rmeta --extern hex=/home/runner/work/penumbra/penumbra/target/debug/deps/libhex-6bd2f803b6087ede.rmeta --extern penumbra_proto=/home/runner/work/penumbra/penumbra/target/debug/deps/libpenumbra_proto-7dc9b8e5e9ce2f88.rmeta --extern pin_project=/home/runner/work/penumbra/penumbra/target/debug/deps/libpin_project-492ab97da17e700e.rmeta --extern reqwest=/home/runner/work/penumbra/penumbra/target/debug/deps/libreqwest-26afb4aba10d64bb.rmeta --extern serde_json=/home/runner/work/penumbra/penumbra/target/debug/deps/libserde_json-6a644f97da992a29.rmeta --extern structopt=/home/runner/work/penumbra/penumbra/target/debug/deps/libstructopt-543363e353eaa22b.rmeta --extern tendermint=/home/runner/work/penumbra/penumbra/target/debug/deps/libtendermint-cedabfa36b53efd5.rmeta --extern tendermint_proto=/home/runner/work/penumbra/penumbra/target/debug/deps/libtendermint_proto-33de9b37a16e7455.rmeta --extern tokio=/home/runner/work/penumbra/penumbra/target/debug/deps/libtokio-746baaa1a8360ed9.rmeta --extern tower=/home/runner/work/penumbra/penumbra/target/debug/deps/libtower-f150a8eb423b7c81.rmeta --extern tower_abci=/home/runner/work/penumbra/penumbra/target/debug/deps/libtower_abci-3ca1209c067a3cc4.rmeta --extern tracing=/home/runner/work/penumbra/penumbra/target/debug/deps/libtracing-833d21e8994ca489.rmeta --extern tracing_subscriber=/home/runner/work/penumbra/penumbra/target/debug/deps/libtracing_subscriber-6dd379276acc4ce1.rmeta --crate-version 0.1.0` (exit status: 1)
warning: build failed, waiting for other jobs to finish...
error: build failed

[jyn514]

Duplicate of #84738, but thanks for the link to your codebase, that will make it easier to reproduce :)