Unable to emit llvm-bc when CARGO_INCREMENTAL is set

[jaybutera]

When building with the rustc argument to emit an llvm bc file
cargo rustc -v -- --emit llvm-bc

Cargo builds successfully but prints the warning
warning: ignoring emit path because multiple .bc files were produced

Doing a recursive search for all *.bc files from root, I can see that the bc file I'm wanting was not generated, but there are a lot of bc files in ./target/debug/incremental/.

So I turned off incremental building export CARGO_INCREMENTAL=0 and cleared the target directory, then ran the build command again. This time the correct bc file is generated in ./target/debug/deps

[ehuss]

Thanks for the report. This sounds like a rustc issue, so I have transferred this to rust-lang/rust.

This seems suspiciously similar to #48147, so I'm not sure if it is a dupe.

Basic repro:

rustc foo.rs --emit=llvm-bc  -C incremental=.

vs

rustc foo.rs --emit=llvm-bc 

[Enselic]

Triage: Fixed in nightly-2020-04-05, maybe #70156 which added a test. Other candidates:

$ git log  ^74bd074eefcf4915c73d1ab91bc90859664729e6 853c4774e26ea97b45fe74de9a6f68e526784323 --no-merges --oneline
dcf70044de3 Update src/tools/publish_toolstate.py
8ad149a0e08 typeck/type_of: only early-bound and (free) late-bound lifetimes are parameters.
ea7999b4f35 tests: add tests for lifetime and const params of opaque types.
8807b00dd83 typeck/type_of: let wfcheck handle duplicate generics in opaque types' substs.
8e9a5d928a0 typeck/type_of: let wfcheck handle concrete types in opaque types' substs.
a98b5340d17 typeck/type_of: don't ignore incorrect defining uses of opaque types.
64651138524 typeck/type_of: simplify checking of opaque types with multipler defining uses.
f86b078e2df Add hash of source files in debug info
328366d0259 update openssl-src to 111.8.1+1.1.1f
98ead3e636a Update -Ccodegen-units docs wrt incr. comp. in rustc book.
408e6e3dbd8 Add a test case for incremental + codegen-units interaction.
1e5b4594e1a Make the rustc respect the `-C codegen-units` flag in incremental mode.
4387a8b96e4 Move rustc-guide submodule to rustc-dev-guide
57b7203047f add basic IP support in HermitCore

Let's assume this case is tested for and close this as fixed.