GeezerVison

Fixes #2023.

Problem

crawlers::nuget_crawler::tests::solution_roots_and_unrestored_projects_keep_the_walk fails every time on a machine with any package in ~/.nuget/packages. It passes in CI only because the runners' NuGet cache is empty. Issue #2023 has the repro.

While reproducing it I found a second test with the same dependence, an_uncovered_sub_project_keeps_the_walk. That one is also order-dependent: neither test was #[serial], so both ran alongside the serial tests in the same module that point NUGET_PACKAGES and HOME at their own warm folders. With one host package planted (~/.nuget/packages/zz.hostpkg/9.9.9), 30 loops of cargo test -p socket-patch-core --lib nuget_crawler on the partial fix gave:

• 15 failures of solution_roots_… (left had an extra pkg:nuget/[email protected])
• 8 failures of an_uncovered_…, which passed only in runs where a concurrent serial test happened to have NUGET_PACKAGES set

Root cause

An unscoped project-mode crawl (a solution root, or a project with no parsed restore) always adds the global packages folder NuGet would restore into as search root 3 (crawl_roots, via global_packages_folder → nuget_home()). The tests built their packages in a temp shared-cache but left that folder pointing at the process env and home, which belong to the host and to whichever serial test is running at the time.

Fix (test-only)

• New `crawl_local(cwd)` test helper. For the duration of the crawl it sets `NUGET_PACKAGES`, under `crate::test_env::EnvGuard`, to a tempdir holding exactly one package, `[email protected]`. All six project-mode crawl tests use it and are now `#[serial]`. The two unscoped-walk tests must list `global.only`, which shows root 3 is walked. The four scoped tests must leave it out, which shows scoping excludes the global folder; before this PR they passed only because `seen` dedups by purl. Mutation check: with root 3 dropped from `crawl_roots`, 3 tests fail.
• `test_nuget_home_env_var` and `test_nuget_home_empty_env_var_falls_back_to_default` move from bare `set_var`/`remove_var` onto `EnvGuard`, so a failed assertion can't leak `NUGET_PACKAGES` into later tests.

The crawler itself doesn't change. The unscoped walk the tests pin (#427 / #1183) stays the same.

Not fixed here, left as follow-ups from `/code-review high`:

• `NugetEnv` still hand-rolls a restore-on-drop that duplicates `EnvGuard`.
• `tests/crawler_nuget_e2e.rs` still saves and restores `NUGET_PACKAGES` by hand around an `unwrap()`.
• `crawl_local` doesn't isolate the user-level NuGet.Config. No current walk test depends on it.

Proof

So in CI this is latent: no failure reproduced in 150 CI-like runs. The fix makes the tests hermetic for dev machines and removes the cross-test env race. cargo clippy -p socket-patch-core --all-features -D warnings (CI's command) is clean, and rustfmt shows no diff on the touched file. With --all-targets, my local clippy reports 39 lints that main has too; none are in this file.

Tests moved or removed

None. Every test still runs where it ran before (test jobs, PR and merge queue).

https://claude.ai/code/session_011f9aeRytjzpRh8AHn2i5Qh

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