chore: add CI env variable configurations (#1672)

This branch adds some environment variables to configure *all* CI jobs.
In particular, we:

- disable incremental compilation
- increase the number of retries for network requests in `cargo` and
  `rustup`
- emit shortened backtraces from panics

This config was blatantly stolen from linkerd/linkerd2-proxy#7137. :)

Incremental compilation is useful as part of an edit-build-test-edit
cycle, as it lets the compiler avoid recompiling code that hasn't
changed. However, on CI, we're not making small edits; we're almost
always building the entire project from scratch. Thus, incremental
compilation on CI actually introduces *additional* overhead to support
making future builds faster...but no future builds will ever occur in
any given CI environment.

See https://matklad.github.io/2021/09/04/fast-rust-builds.html#ci-workflow
for details.

Increasing retries for network requests should help reduce flakiness a
bit.

Author: hawkw

Diff for: .github/workflows/CI.yml

@@ -6,6 +6,27 @@ on:
     - master
   pull_request: {}
 
+env:
+  # Disable incremental compilation.
+  #
+  # Incremental compilation is useful as part of an edit-build-test-edit cycle,
+  # as it lets the compiler avoid recompiling code that hasn't changed. However,
+  # on CI, we're not making small edits; we're almost always building the entire
+  # project from scratch. Thus, incremental compilation on CI actually
+  # introduces *additional* overhead to support making future builds
+  # faster...but no future builds will ever occur in any given CI environment.
+  #
+  # See https://matklad.github.io/2021/09/04/fast-rust-builds.html#ci-workflow
+  # for details.
+  CARGO_INCREMENTAL: 0
+  # Allow more retries for network requests in cargo (downloading crates) and
+  # rustup (installing toolchains). This should help to reduce flaky CI failures
+  # from transient network timeouts or other issues.
+  CARGO_NET_RETRY: 10
+  RUSTUP_MAX_RETRIES: 10
+  # Don't emit giant backtraces in the CI logs.
+  RUST_BACKTRACE: short
+
 jobs:
   check-msrv:
     # Run `cargo check` on our minimum supported Rust version (1.42.0).

Diff for: .github/workflows/audit.yml

@@ -1,7 +1,30 @@
 name: Security audit
+
 on:
   schedule:
     - cron: '0 0 * * *'
+    
+env:
+  # Disable incremental compilation.
+  #
+  # Incremental compilation is useful as part of an edit-build-test-edit cycle,
+  # as it lets the compiler avoid recompiling code that hasn't changed. However,
+  # on CI, we're not making small edits; we're almost always building the entire
+  # project from scratch. Thus, incremental compilation on CI actually
+  # introduces *additional* overhead to support making future builds
+  # faster...but no future builds will ever occur in any given CI environment.
+  #
+  # See https://matklad.github.io/2021/09/04/fast-rust-builds.html#ci-workflow
+  # for details.
+  CARGO_INCREMENTAL: 0
+  # Allow more retries for network requests in cargo (downloading crates) and
+  # rustup (installing toolchains). This should help to reduce flaky CI failures
+  # from transient network timeouts or other issues.
+  CARGO_NET_RETRY: 10
+  RUSTUP_MAX_RETRIES: 10
+  # Don't emit giant backtraces in the CI logs.
+  RUST_BACKTRACE: short
+
 jobs:
   security_audit:
     runs-on: ubuntu-latest