Document lib before bin.

[ehuss]

This changes it so that documenting a library is required to finish before documenting a binary. The issue is that the binary may have intra-doc links to the library. If they are documented concurrently, then the links will sometimes fail (since it is a race). Or, if doing cargo doc --bins, then the library docs wouldn't exist at all.

Note that in the tests this introduces some more name collisions if you just run cargo doc --bins and there is a colliding library/binary name. There is some risk that someone might be trying to run the commands separately to get around the collision error, but I think it is unlikely.

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

@bors: r+

[bors]

📌 Commit a09fbf2 has been approved by alexcrichton

[bors]

⌛ Testing commit a09fbf2 with merge 3aaa8f9...

[bors]

☀️ Test successful - checks-actions
Approved by: alexcrichton
Pushing 3aaa8f9 to master...

[Mark-Simulacrum]

FWIW, this caused an error in rustc-perf on the token-stream-stress benchmark:

stderr=warning: output filename collision.
The bin target `token-stream-stress` in package `token-stream-stress v0.0.0 (/tmp/.tmp4JOGMM)` has the same output filename as the lib target `token-stream-stress` in package `token-stream-stress v0.0.0 (/tmp/.tmp4JOGMM)`.
Colliding filename is: /tmp/.tmp4JOGMM/target/doc/token_stream_stress/index.html
The targets should have unique names.
This is a known bug where multiple crates with the same name use
the same path; see <https://github.com/rust-lang/cargo/issues/6313>.
 Documenting token-stream-stress v0.0.0 (/tmp/.tmp4JOGMM)
"/home/collector/rustc-perf/cache/3ee016ae4d4c6ee4a34faa2eb7fdae2ffa7c9b46/bin/rustdoc" ["--edition=2018", "--crate-type", "proc-macro", "--crate-name", "token_stream_stress", "src/lib.rs", "-o", "/tmp/.tmp4JOGMM/target/doc", "--error-format=json", "--json=diagnostic-rendered-ansi,future-incompat", "-C", "metadata=49e968af46dd2295", "-L", "dependency=/tmp/.tmp4JOGMM/target/debug/deps", "--extern", "proc_macro", "--crate-version", "0.0.0", "-Adeprecated", "-Aunknown-lints"]
exiting -- non-wrapped rustc
error: could not document `token-stream-stress`

Caused by:
  process didn't exit successfully: `/home/collector/rustc-perf/target/release/rustdoc-fake --edition=2018 --crate-type proc-macro --crate-name token_stream_stress src/lib.rs -o /tmp/.tmp4JOGMM/target/doc --error-format=json --json=diagnostic-rendered-ansi,future-incompat -C metadata=49e968af46dd2295 -L dependency=/tmp/.tmp4JOGMM/target/debug/deps --extern proc_macro --crate-version 0.0.0` (exit status: 1)


 stdout=

I'm going to work around it by not trying to renaming the bin target (which I think should work), but wanted to make a note of it as "one thing that broke" :)

[pnkfelix]

Is cargo doing anything to lint against these sorts of name collisions? (Should it?)