fix(runner): init std.testing.io_instance — fixes #44

[apotema]

Summary

Fixes a linux-only deadlock for every consumer using zspec's mode: .simple test_runner whose tests touch std.testing.io.

std.testing declares pub var io_instance: Io.Threaded = undefined and pub const io = io_instance.io(). Threaded.io(t) bakes &io_instance into the returned Io's userdata at comptime — so without a runtime init, every call site is talking to a zero-initialized Threaded (no worker pool). On linux that deadlocks; on macOS more zero-init paths happen to work, hiding the bug.

The stdlib's terminal runner already does the right thing (lib/compiler/test_runner.zig:273-282 — per-test init+deinit). zspec's .simple runner didn't.

Fix

Single-shot testing.io_instance = .init(testing.allocator, .{}) at the top of runner.main(). Same memory address that comptime-baked Io.userdata pointers already reference — they now point at a properly initialized Threaded with a real worker pool.

Per-test re-init (matching the stdlib) is cheaper to skip in a .simple runner: 160 tests × spinning up a worker pool is way more than one global init covers.

Test plan

• New tests/testing_io_test.zig exercises the two deadlock signatures from runner does not initialize std.testing.io_instance — tests using std.testing.io deadlock on linux #44 (tmpDir + writeFile round-trip; readFileAlloc on a missing path) under the .simple runner. Both passed in <5 ms locally and in an ubuntu:24.04 docker container; both would have hung for 6 h on linux before this fix.
• Full zig build test passes locally on macOS (57/57) and in the linux container.
• End-to-end consumer verification: labelle-toolkit/labelle-gui@6e11736 carried an equivalent fix as a project-local beforeAll hook — that project's test suite had been timing out at 6 h on every linux CI run since the 0.16 migration; it now passes 162/162 in <1 s.

Closes #44.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes a Linux-only deadlock in zspec’s .simple test_runner when tests use std.testing.io by initializing std.testing.io_instance in the custom runner, and adds a regression test to ensure this remains covered.

Changes:

• Initialize/deinitialize std.testing.io_instance in src/runner.zig so std.testing.io has a properly initialized Io.Threaded worker pool.
• Add a regression test that exercises the previously-deadlocking std.testing.io code paths under the .simple runner.
• Wire the new regression test into zig build test via build.zig, explicitly using the .simple runner.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/runner.zig	Adds one-time initialization of std.testing.io_instance for the .simple runner to prevent Linux deadlocks.
tests/testing_io_test.zig	New regression tests covering tmpDir + writeFile + readFileAlloc and missing-path readFileAlloc under std.testing.io.
build.zig	Adds the new regression test executable and includes it in the main test build step, routed through the .simple runner.

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