give more helpful error messages for SGX_MODE and IAS_MODE settings

[cbeck88]

Many projects submodule mobilecoin.git and do not have it's BUILD.md document which describes how to set these variables.

It frequently happens that newly onboarded developers, or partners like copper, run into a build error that looks like this:

   Compiling libp2p-plaintext v0.37.0
   Compiling libp2p-floodsub v0.40.1
   Compiling slog-envlogger v2.2.0
error: failed to run custom build command for `mc-attest-core v4.0.2 (/home/chris/mobilecoinofficial/deqs/mobilecoin/attest/core)`

Caused by:
  process didn't exit successfully: `/home/chris/mobilecoinofficial/deqs/target/debug/build/mc-attest-core-fa6d778110b3deb5/build-script-build` (exit status: 101)
  --- stderr
  thread 'main' panicked at 'Could not parse SGX environment: Variable(NotPresent)', mobilecoin/attest/core/build.rs:8:41
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This error doesn't contain enough information for them to understand and fix the problem, so they end up asking us for help.

We can follow the rust tradition of trying to make build-time errors contain enough information to understand how to address the problem.

This commit tries to make the message say what variable was not present, and also contain a link to the mobilecoin.git BUILD.md so that they can learn more.

[nick-mobilecoin]

I think this is a step in the right direction, but it still misses the intent in the PR description.

I'm guessing expect() uses debug instead of display, kind of surprised but maybe it's a compile time optimization.

error: failed to run custom build command for `mc-attest-core v4.0.2 (/home/nick/git/mobilecoin/attest/core)`

Caused by:
  process didn't exit successfully: `/home/nick/git/mobilecoin/target/debug/build/mc-attest-core-765438a6f0b96ded/build-script-build` (exit status: 101)
  --- stderr
  thread 'main' panicked at 'Could not parse SGX environment: Variable("REALLY", NotPresent)', attest/core/build.rs:8:41
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...
error: failed to run custom build command for `mc-attest-ake v4.0.2 (/home/nick/git/mobilecoin/attest/ake)`

Caused by:
  process didn't exit successfully: `/home/nick/git/mobilecoin/target/debug/build/mc-attest-ake-2d6c54bb8b6bee8d/build-script-build` (exit status: 101)
  --- stderr
  thread 'main' panicked at 'Could not parse SGX environment: Variable("REALLY", NotPresent)', attest/ake/build.rs:8:41
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
➜  mobilecoin git:(sgx_mode_error_messages) ✗ rg "Could not parse SGX"
consensus/enclave/build.rs
19:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

consensus/enclave/trusted/build.rs
21:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

fog/view/enclave/build.rs
19:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

fog/view/enclave/trusted/build.rs
21:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

fog/ingest/enclave/build.rs
19:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

fog/ingest/enclave/trusted/build.rs
21:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

fog/ledger/enclave/build.rs
19:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

fog/ledger/enclave/trusted/build.rs
21:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

attest/core/build.rs
8:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

attest/ake/build.rs
8:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

attest/verifier/build.rs
281:    let sgx = SgxEnvironment::new(&env).expect("Could not parse SGX environment");

[cbeck88]

damn, thank you. i guess i will not derive Debug, and make Debug forward to Display

[nick-mobilecoin]

It looks like all usages of SgxEnvironment::new() chain with expect() so maybe new() can be updated to panic and clean up the error message there.
Another thought is to remove new and implement TryFrom and From since new only has one parameter.
Either way I think the 11 instances of the same expect hint that maybe they should be conslidated

[nick-mobilecoin]

damn, thank you. i guess i will not derive Debug, and make Debug forward to Display

or that works too :)

[nick-mobilecoin]

Looks good now

Caused by:
  process didn't exit successfully: `/home/nick/git/mobilecoin/target/debug/build/mc-attest-core-765438a6f0b96ded/build-script-build` (exit status: 101)
  --- stderr
  thread 'main' panicked at 'Could not parse SGX environment: There was an error reading an environment variable REALLY: environment variable not found. Please see https://github.com/mobilecoinfoundation/mobilecoin/blob/master/BUILD.md#build-configuration for more information.', attest/core/build.rs:8:41

[github-actions]

❌ Heads up, I tried building full-service using this branch and it failed.
Build logs can be found by inspecting the github action run Check that repositories submoduling us will still build after this PR / full-service or by clicking here.

[NotGyro]

This looks good to me, the error messages are much more helpful and clear.