ci: add opt out env variable to temporarily prevent using build-dir v2 in nightly runs

[Alan632]

Summary

The new build-dir v2 layout was added in Rust nightly by this pr rust-lang/rust#159857 which breaks tooling in our cargo-wdk and pipeline.

This PR sets the opt out environment variable in the build and test workflows to continue using the v1 build-dir layout until cargo-wdk can be updated to support the build-dir layout v2.

reference PR's:

• Enable build-dir layout v2 on nightly by default rust-lang/cargo#17258
• Reworked how we enable the new build-dir layout on nightly rust-lang/cargo#17272

info on the new build directory layout:

• https://blog.rust-lang.org/2026/03/13/call-for-testing-build-dir-layout-v2/

GitHub Issue Link: #709

[Copilot]

Pull request overview

This PR adds a Cargo opt-out environment variable to the CI workflows to keep using the legacy (v1) temporary build directory layout, working around Rust nightly’s new build-dir layout v2 that currently breaks cargo-wdk tooling in this repository.

Changes:

• Set __CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT=1 at the workflow level for the test workflow.
• Set __CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT=1 at the workflow level for the build workflow.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/test.yaml	Adds the Cargo build-dir layout v2 opt-out env var for CI test runs.
.github/workflows/build.yaml	Adds the Cargo build-dir layout v2 opt-out env var for CI build runs (alongside existing RUSTFLAGS).

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.47%. Comparing base (66223e9) to head (1c34c7e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #707   +/-   ##
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  Coverage   80.47%   80.47%           
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  Files          26       26           
  Lines        5722     5722           
  Branches     5722     5722           
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  Hits         4605     4605           
  Misses        989      989           
  Partials      128      128           

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Suppressed comments (1)

.github/workflows/build.yaml:18

• CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT does not appear to be a Cargo-recognized env var for opting out of build-dir layout v2, so this likely has no effect and nightly builds may still use layout v2. Upstream Cargo uses __CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT=1 as the temporary opt-out flag.

env:
  # TODO: Remove when cargo-wdk supports Cargo build-dir layout v2.
  CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT: 'false'

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Suppressed comments (2)

.github/workflows/test.yaml:18

• The env var being set here (CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT) does not appear to be Cargo’s opt-out for the nightly-default build-dir layout v2. Cargo’s own implementation uses __CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT=1 as the temporary opt-out, so this workflow may not actually prevent layout v2 from being used.

env:
  # TODO: Remove when cargo-wdk supports Cargo build-dir layout v2 (see https://github.com/microsoft/windows-drivers-rs/issues/709).
  CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT: 'false'

.github/workflows/build.yaml:21

• This sets CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT, but Cargo’s nightly-default build-dir layout v2 opt-out is implemented via __CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT=1. Using the temporary opt-out env var here is more likely to reliably force the legacy (v1) layout in nightly.

env:
  # TODO: Remove when cargo-wdk supports Cargo build-dir layout v2 (see https://github.com/microsoft/windows-drivers-rs/issues/709).
  CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT: 'false'

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Suppressed comments (1)

crates/cargo-wdk/tests/test_utils/mod.rs:316

• The TODO references removal from test.yaml, but this env var is also set in other workflows (e.g., build.yaml). To avoid the comment becoming misleading, consider wording it in terms of CI/workflows generally rather than a specific file name.

            // TODO: Remove this whitelist once the env var is removed from test.yaml (see https://github.com/microsoft/windows-drivers-rs/issues/709)