cargo doc fails on found duplicate lang item 'panic_impl' dependency issue (no_std)

[tgross35]

It seems like cargo doc fails is there is a dependency that has a panic_impl and a binary that defines it as well, even if the dependency is never imported.

I ran into this issue when I had >1 no_std bin per crate, where one binary had a custom panic_impl and another used that from a dependency. Minimal reproduction:

crate1 % tree
.
├── Cargo.lock
├── Cargo.toml
└── src
    └── main.rs

[package]
name = "crate1"
version = "0.1.0"
edition = "2021"

[dependencies]
# this dependency adds `panic_impl`, but it is never imported or used
flash-algorithm = "0.3.0"

// main.rs
#![no_std]
#![no_main]

#[panic_handler]
fn panic(_: &core::panic::PanicInfo) -> ! {
    loop {}
}

The following works:

cargo c --target thumbv7em-none-eabihf
cargo build --target thumbv7em-none-eabihf

But this fails (also when specifying target)

% cargo doc
 Documenting flash-algorithm v0.3.0
 Documenting crate1 v0.1.0 (/crate1)
error[E0152]: found duplicate lang item `panic_impl`
 --> src/main.rs:5:1
  |
5 | fn panic(_: &core::panic::PanicInfo) -> ! {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: the lang item is first defined in crate `flash_algorithm`.
  = note: first definition in `flash_algorithm` loaded from /crate1/target/debug/deps/libflash_algorithm-53fc8a5d1bd6046f.rmeta
  = note: second definition in the local crate (`crate1`)

For more information about this error, try `rustc --explain E0152`.
error: could not document `crate1`

Caused by:
  process didn't exit successfully: `rustdoc --edition=2021 --crate-type bin --crate-name crate1 src/main.rs -o /crate1/target/doc --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=147 --document-private-items '-Arustdoc::private-intra-doc-links' -C metadata=90e18e4cce856399 -L dependency=/crate1/target/debug/deps --extern flash_algorithm=/crate1/target/debug/deps/libflash_algorithm-53fc8a5d1bd6046f.rmeta --crate-version 0.1.0` (exit status: 1)

rustc --version --verbose:

rustc 1.69.0-nightly (1e225413a 2023-01-28)
binary: rustc
commit-hash: 1e225413a21fa69570bd3fefea9eb05e33f8b917
commit-date: 2023-01-28
host: x86_64-apple-darwin
release: 1.69.0-nightly
LLVM version: 15.0.7

@rustbot label +T-rustdoc

[tgross35]

Possibly similar cause: #68427

[tgross35]

Seems like this happens even with --no-deps so not really a good workaround, yuck...

[GuillaumeGomez]

I can't reproduce the bug locally. Do you still have the issue?

[tgross35]

Interesting - it looks like it was broken on nightly-2023-01-28 but working on my current rustc 1.69.0-nightly (2d14db321 2023-02-15). Probably not worth bisecting, but maybe a regression test would be good if there isn't one?

% cargo +nightly-2023-01-28 doc   
   Compiling flash-algorithm v0.3.0
 Documenting flash-algorithm v0.3.0
 Documenting testme v0.1.0 (/Users/tmgross/Documents/Projects/testme)
error[E0152]: found duplicate lang item `panic_impl`
 --> src/main.rs:5:1
  |
5 | fn panic(_: &core::panic::PanicInfo) -> ! {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: the lang item is first defined in crate `flash_algorithm`.
  = note: first definition in `flash_algorithm` loaded from /Users/tmgross/Documents/Projects/testme/target/debug/deps/libflash_algorithm-53fc8a5d1bd6046f.rmeta
  = note: second definition in the local crate (`testme`)

For more information about this error, try `rustc --explain E0152`.
error: could not document `testme`

Caused by:
  process didn't exit successfully: `rustdoc --edition=2021 --crate-type bin --crate-name testme src/main.rs -o /Users/tmgross/Documents/Projects/testme/target/doc --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=181 --document-private-items '-Arustdoc::private-intra-doc-links' -C metadata=179b40203cf7ab78 -L dependency=/Users/tmgross/Documents/Projects/testme/target/debug/deps --extern flash_algorithm=/Users/tmgross/Documents/Projects/testme/target/debug/deps/libflash_algorithm-53fc8a5d1bd6046f.rmeta --crate-version 0.1.0` (exit status: 1)

% cargo doc
 Documenting flash-algorithm v0.3.0
 Documenting testme v0.1.0 (/Users/tmgross/Documents/Projects/testme)
    Finished dev [unoptimized + debuginfo] target(s) in 1.91s

[GuillaumeGomez]

Agreed, wanna add one? Otherwise I plan to do it in the next hours.

[tgross35]

I'm not too familiar with the test patterns for rustdoc, so I'll just leave it to you if you don't mind

[GuillaumeGomez]

No problem!