Crate can't build offline

[0xngold]

Summary

Expected behavior: windows-rs builds successfully offline with a local-registry
Actual behavior: windows-rs build fails with a cryptic error message

It seems there are three sub-bugs here:

• cargo metadata doesn't work offline, even if windows-rs was supplying --offline (see cargo metadata --offline requires Internet access rust-lang/cargo#9273).
• windows-rs discards the errors from the cargo metadata invocation. This makes debugging tricky.
• Given that cargo metadata doesn't currently work offline, is there another place we can get this workspace_root from?

Details

Error example

error: proc macro panicked
 --> C:\Users\some_user\.cargo\registry\src\-b20c50870c528e96\windows-0.3.1\build.rs:2:5
2 |     windows_macros::build!();
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^

  = help: message: Cargo metadata \\?\C:\src\.rustup\toolchains\stable-x86_64-pc-windows-msvc\bin\cargo.exe did not contain `workspace_root` key. Got stdout . Got stderr     
          Updating crates.io index
          warning: spurious network error (2 tries remaining): failed to send request: The server name or address could not be resolved
          ; class=Os (2)
          warning: spurious network error (1 tries remaining): failed to send request: The server name or address could not be resolved
          ; class=Os (2)
          error: failed to get `const-sha1` as a dependency of package `windows v0.3.1 (C:\Users\some_user\.cargo\registry\src\-b20c50870c528e96\windows-0.3.1)`

          Caused by:
            failed to load source for dependency `const-sha1`

          Caused by:
            Unable to update registry `https://github.com/rust-lang/crates.io-index`

          Caused by:
            failed to fetch `https://github.com/rust-lang/crates.io-index`

          Caused by:
            failed to send request: The server name or address could not be resolved
            ; class=Os (2)

          .
   Ran from "C:\\Users\\some_user\\.cargo\\registry\\src\\-b20c50870c528e96\\windows-0.3.1"

error: aborting due to previous error

Repro steps

1. Create a binary crate C that depends on windows-rs.
2. Use cargo local-registry to create a local registry for C's dependencies.
3. Try to build C with the local registry replacing crates.io. The build should fail with a cryptic error from the windows-rs build. To reproduce the error message I have above, modifying this line inside the local registry's copy of windows_winmd crate. There is almost certainly a simpler repro, but a repro shouldn't be strictly necessary to verify this bug has been fixed.

[kennykerr]

Unfortunately, I'm not aware of any other way to get the workspace dir. I had hoped there would be an environment variable, as there is for OUT_DIR, CARGO_MANIFEST_DIR, and so on. Reading the result of cargo metadata is certainly not ideal, but that's all I could find.

From what I can tell, there have been attempts to add such an environment variable but it has always run into blocking issues. So it may be best to fix the offline bug in cargo metadata that you mentioned.

[rylev]

cargo metadata has an offline flag we can pass it which will not go to the network. It still has the workspace dir available.

[kennykerr]

@rylev the original issue mentions that the offline flag doesn't work.

[rylev]

Whoops, sorry totally missed that!

[kennykerr]

I did however just try running cargo metadata --format-version=1 --no-deps without an internet connection and it works fine for me using cargo 1.52.0-nightly.

[kennykerr]

I have added the --offline flag for good measure, but it doesn't appear to make a difference. Anyway, I don't think there's anything else I can do from my end.

[0xngold]

Thanks! Version 0.5.0 fixes the issue for me (the only change there seems to be adding --format-version=1 --no-deps; previously I was on 0.3.1).