Merging this PR will regress 2 benchmarks

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 3 improved benchmarks
❌ 3 (👁 1) regressed benchmarks
✅ 179 untouched benchmarks
🆕 12 new benchmarks
⏩ 53 skipped benchmarks1

Performance Changes

Comparing cod-2931-prepare-compatibility-with-vitest-5 (eec7ec7) with main (1999ec9)

Footnotes

1. 53 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

Greptile Summary

This PR adds Vitest 5 support to the CodSpeed Vitest plugin. The main changes are:

• A new Vitest 5 benchmark provider path.
• Legacy Vitest 3/4 runner code moved under src/legacy.
• Shared instrumentation and walltime result conversion helpers.
• Updated Vitest dependency ranges and a Vitest 4 example project.

Confidence Score: 4/5

The new Vitest 5 path can record distinct benchmarks under one CodSpeed URI, and legacy fallback can skip instrumentation.

• Multiple bench() registrations in one Vitest 5 group can share one CodSpeed benchmark identity.
• Unknown Vitest version detection can route supported Vitest 3/4 runs through the v5 gating path.
• The remaining changes are mostly layout, tests, examples, and shared helper refactors.

packages/vitest-plugin/src/v5/provider.ts and packages/vitest-plugin/src/vitestBackend.ts

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Vitest run] --> B{Detected Vitest major}
  B -->|3 or 4| C[Legacy backend]
  C --> D[legacy analysis or walltime runner]
  B -->|5 or newer| E[V5 backend]
  E --> F{benchmark enabled}
  F -->|no| G[default Vitest behavior]
  F -->|yes| H[v5 benchmark provider]
  H --> I{CodSpeed mode}
  I -->|analysis or simulation| J[run one measured pass]
  I -->|walltime| K[run tinybench with hooks]
  J --> L[CodSpeed benchmark result]
  K --> L

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
  A[Vitest run] --> B{Detected Vitest major}
  B -->|3 or 4| C[Legacy backend]
  C --> D[legacy analysis or walltime runner]
  B -->|5 or newer| E[V5 backend]
  E --> F{benchmark enabled}
  F -->|no| G[default Vitest behavior]
  F -->|yes| H[v5 benchmark provider]
  H --> I{CodSpeed mode}
  I -->|analysis or simulation| J[run one measured pass]
  I -->|walltime| K[run tinybench with hooks]
  J --> L[CodSpeed benchmark result]
  K --> L

Comments Outside Diff (2)

1. packages/vitest-plugin/src/v5/provider.ts, line 1778 (link)

   Group URI Drops Benchmark Name

   When a Vitest 5 test registers multiple bench(name, ...) entries, this provider builds one URI from the group and reuses it for every registration. The legacy paths append the benchmark task name, so the new path can attribute distinct measurements to the same CodSpeed benchmark and merge or overwrite their results.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: packages/vitest-plugin/src/v5/provider.ts
   Line: 1778
   
   Comment:
   **Group URI Drops Benchmark Name**
   
   When a Vitest 5 test registers multiple `bench(name, ...)` entries, this provider builds one URI from the group and reuses it for every registration. The legacy paths append the benchmark task name, so the new path can attribute distinct measurements to the same CodSpeed benchmark and merge or overwrite their results.
   
   How can I resolve this? If you propose a fix, please make it concise.

   

2. packages/vitest-plugin/src/vitestBackend.ts, line 1910-1911 (link)

   Unknown Version Selects V5

   When Vitest resolution from process.cwd() fails for a supported Vitest 3/4 project, this fallback selects the v5 backend. A v3/v4 benchmark run then has no test.benchmark.enabled flag, so config() returns undefined and the legacy runner is never installed, leaving CodSpeed runs uninstrumented without an error.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: packages/vitest-plugin/src/vitestBackend.ts
   Line: 1910-1911
   
   Comment:
   **Unknown Version Selects V5**
   
   When Vitest resolution from `process.cwd()` fails for a supported Vitest 3/4 project, this fallback selects the v5 backend. A v3/v4 benchmark run then has no `test.benchmark.enabled` flag, so `config()` returns `undefined` and the legacy runner is never installed, leaving CodSpeed runs uninstrumented without an error.
   
   How can I resolve this? If you propose a fix, please make it concise.

   

Fix the following 3 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 3
packages/vitest-plugin/src/v5/provider.ts:1778
**Group URI Drops Benchmark Name**

When a Vitest 5 test registers multiple `bench(name, ...)` entries, this provider builds one URI from the group and reuses it for every registration. The legacy paths append the benchmark task name, so the new path can attribute distinct measurements to the same CodSpeed benchmark and merge or overwrite their results.

### Issue 2 of 3
packages/vitest-plugin/src/vitestBackend.ts:1910-1911
**Unknown Version Selects V5**

When Vitest resolution from `process.cwd()` fails for a supported Vitest 3/4 project, this fallback selects the v5 backend. A v3/v4 benchmark run then has no `test.benchmark.enabled` flag, so `config()` returns `undefined` and the legacy runner is never installed, leaving CodSpeed runs uninstrumented without an error.

### Issue 3 of 3
packages/vitest-plugin/src/globalSetup.ts:15
**Untracked TODO Comment**

This new TODO has no Linear issue reference, which violates the repository rule for TODO comments. Please change it to the `TODO(COD-XXX): ...` form or remove it.

```suggestion
// TODO(COD-XXX): Check if this can be avoided
```

Reviews (1): Last reviewed commit: "feat(vitest-plugin): use the vitest 5 be..." | Re-trigger Greptile