Actual error seems to be stripped from the error message

I am seeing the following error:

error: failed to run custom build command for `near-test-contracts v0.0.0 (/home/matklad/projects/nearcore/runtime/near-test-contracts)`

Caused by:
  process didn't exit successfully: `/home/matklad/projects/nearcore/target/release/build/near-test-contracts-c00a188e349b5e55/build-script-build` (exit status: 1)
  --- stderr
  info: downloading component 'rust-std' for 'wasm32-unknown-unknown'
  error: component download failed for rust-std-wasm32-unknown-unknown: could not rename downloaded file from '/home/matklad/.rustup/downloads/939f4a53a3b000e026d1da8df604ec4cdae1b3ced784388f152204b8d5331ec3.partial' to '/home/matklad/.rustup/downloads/939f4a53a3b000e026d1da8df604ec4cdae1b3ced784388f152204b8d5331ec3'
  command `"rustup" "target" "add" "wasm32-unknown-unknown"` exited with non-zero status: ExitStatus(ExitStatus(256))
warning: build failed, waiting for other jobs to finish...

I think it is coming from https://github.com/rust-lang/rustup/blob/c33cb5ed7fc2854eab7f3cfb1fa6d012b13a8f6c/src/utils/utils.rs#L636-L643

There's some underlying io::Error which should hopefully tell me why the rename fails but it isn't visible in the error mesage .

Read src/utils/utils.rs around lines 636-643, then reproduce the failure with rustup target add wasm32-unknown-unknown. Confirm that the underlying io::Error explaining the failed rename is included in the reported error message.