Miri sysroot keeps being rebuilt when running `./x miri` multiple times

[RalfJung]

When I do ./x miri std -- f64 && ./x miri std -- f64, it re-builds the Miri sysroot for the second invocation. That should not happen, it should cache the sysroot. I am pretty sure (but not 100% sure) this used to work properly when I added ./x miri.

@onur-ozkan you changed this code recently in #137215; could that have caused this problem?

[onur-ozkan]

I tested on current latest HEAD (ad27045) and ./x miri std -- f64 && ./x miri std -- f64 did not re-build for me 🤔

[jieyouxu]

AFAICT #137215 shouldn't be changing RUSTFLAGS or otherwise cause unnecessary invalidation... @RalfJung can you share which commit you're on and what config.toml you're using?

[RalfJung]

I'm on the branch from #137594.

change-id = 125535
[llvm]
download-ci-llvm = "if-unchanged"
ninja = true
[build]
jobs = 12
submodules = false
tools = [
    "miri",
    "clippy",
    "rustdoc",
    "rustfmt",
]
[rust]
download-rustc = false
codegen-units = 0
debug-assertions = true
debug-assertions-std = false
debuginfo-level = 1
incremental = true
codegen-backends = ["llvm"]
deny-warnings = false

[RalfJung]

Oh d'oh... I am silly, sorry for that.

I am working on fixing tests in libstd, and Miri detects the libstd changes and then rebuilds. Nothing else gets rebuilt because only tests change.

Sorry for the noise and thanks for taking a look!