Incremental Compile Bug On Moved Imports

[tustvold]

Whilst working on https://github.com/apache/arrow-rs I keep running into issues where incremental compilation gets confused by types that have been moved from one crate within the workspace to another.

I'm not really sure how to come up with a reproducer, as it seems to rely on stale state from previous builds that I can't find a way to reproduce. However, @carols10cents recommended I file an issue to at least alert you guys that something isn't quite right 😅

An example error would be

$ cargo check
    Checking arrow-array v27.0.0 (/home/raphael/repos/external/arrow-rs/arrow-array)

error[E0432]: unresolved imports `arrow_schema::DECIMAL128_MAX_PRECISION`, `arrow_schema::DECIMAL128_MAX_SCALE`, `arrow_schema::DECIMAL256_MAX_PRECISION`, `arrow_schema::DECIMAL256_MAX_SCALE`, `arrow_schema::DECIMAL_DEFAULT_SCALE`
  --> arrow-array/src/types.rs:26:51
   |
26 |     ArrowError, DataType, IntervalUnit, TimeUnit, DECIMAL128_MAX_PRECISION,
   |                                                   ^^^^^^^^^^^^^^^^^^^^^^^^ no `DECIMAL128_MAX_PRECISION` in the root
27 |     DECIMAL128_MAX_SCALE, DECIMAL256_MAX_PRECISION, DECIMAL256_MAX_SCALE,
   |     ^^^^^^^^^^^^^^^^^^^^  ^^^^^^^^^^^^^^^^^^^^^^^^  ^^^^^^^^^^^^^^^^^^^^ no `DECIMAL256_MAX_SCALE` in the root
   |     |                     |
   |     |                     no `DECIMAL256_MAX_PRECISION` in the root
   |     no `DECIMAL128_MAX_SCALE` in the root
28 |     DECIMAL_DEFAULT_SCALE,
   |     ^^^^^^^^^^^^^^^^^^^^^ no `DECIMAL_DEFAULT_SCALE` in the root

Related to apache/arrow-rs#3177

And goes away with a cargo clean.

Edit: Interestingly it didn't appear to recompile any of the dependent crates, such as arrow-data, despite the fact they have changed... Perhaps this is a cargo bug??

Meta

rustc --version --verbose:

rustc 1.65.0 (897e37553 2022-11-02)
binary: rustc
commit-hash: 897e37553bba8b42751c67658967889d11ecd120
commit-date: 2022-11-02
host: x86_64-unknown-linux-gnu
release: 1.65.0
LLVM version: 15.0.0

[swarmer]

I'm hitting what seems to be a similar bug daily. But in my case I think it's not moved items but rather simply new items (structs, methods) that end up unresolved because the compiler seems to use some stale cache from another branch. cargo clean fixes it. I can't share the project, and I'm not sure how to reproduce this except that it happens after switching branches in a workspace.

After reading this issue, I'm realizing that this may, in fact, always be happening across workspace's crate boundaries for me, but I'm not sure, I'll pay more attention to whether it's always the case.

rustc --version --verbose

rustc 1.80.1 (3f5fd8dd4 2024-08-06)
binary: rustc
commit-hash: 3f5fd8dd41153bc5fdca9427e9e05be2c767ba23
commit-date: 2024-08-06
host: aarch64-apple-darwin
release: 1.80.1
LLVM version: 18.1.7