Renaming the project root dir invalidates compilation cache

[alubbe]

I was surprised to learn that renaming the project root dir invalidates the compilation cache. This is something that happens during every CI and deployment run, making it run quite a bit slower when none of the rust code was actually changed. Is this intentional / is there a way to keep the cache fresh when renaming the directory?

The behaviour can be reproduced as follows (stable 1.12.1):

/$ cargo new rrrrrr
     Created library `rrrrrr` project
/$ cd rrrrrr/
/rrrrrr$ cargo build
   Compiling rrrrrr v0.1.0 (file:///rrrrrr)                            <-- Code gets compiled
    Finished debug [unoptimized + debuginfo] target(s) in 0.11 secs 
/rrrrrr$ cargo build
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs     <-- Code does not re-compile
/rrrrrr$ cargo build
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs     <-- Code does not re-compile
/rrrrrr$ cd ..
/$ mv rrrrrr/ rrrrrr2/
/$ cd rrrrrr2/
/rrrrrr2$ cargo build
   Compiling rrrrrr v0.1.0 (file:///rrrrrr2)                           <-- Code re-compiles
    Finished debug [unoptimized + debuginfo] target(s) in 0.11 secs

[nagisa]

The issue should be filled against cargo.

[alubbe]

Right you are - closing in favour of rust-lang/cargo#3273