goozels

Editor support for gooze, the Go mutation-testing tool. goozels adds autocompletion, hovers, live error-checking, and one-click mutation runs to your editor — for both //gooze:ignore comments in your Go code and your gooze.yaml config file.

It works by sitting in front of gopls (the standard Go language server), so you keep all your normal Go features and simply get gooze ones on top.

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What you get

In your .go files

• Autocomplete the mutagen names in a //gooze:ignore comment:

  x := a + b //gooze:ignore ari⌶      →  arithmetic, …

• Hover a mutagen name to see what it does.

• A warning squiggle if you mistype one:

  y := a - b //gooze:ignore bogus     ⚠ unknown gooze mutagen "bogus"

• ▶ gooze run, gooze list, and 📊 gooze report buttons (code lenses) at the top of every Go file — run mutation testing or open the report without leaving the editor.

• Report results, in your editor. After a run, goozels reads gooze's reports and shows each file's mutation score at the top — e.g. "gooze: 2/10 mutants survived — score 80%" — and marks the approximate spots where mutants survived.

In your gooze.yaml

• Autocomplete config keys (output, run.parallel, log.level, …) and their allowed values.
• Hover a key to see its type, meaning, and default.
• Live validation: unknown keys and bad values (e.g. log.level: loud) are flagged as you type.

The mutagens you can reference in //gooze:ignore are: arithmetic, boolean, numbers, comparison, logical, unary, branch, statement, loop. An empty //gooze:ignore skips them all.

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Requirements

• Go (to install goozels) — https://go.dev/dl/
• gopls — the Go language server: go install golang.org/x/tools/gopls@latest
• gooze — only needed for the run / list buttons: go install gooze.dev/pkg/gooze@latest

goozels finds gopls and gooze on your PATH automatically.

Install

go install gooze.dev/pkg/goozels/cmd/goozels@latest

This puts a goozels binary in your Go bin directory (usually ~/go/bin — make sure it's on your PATH). Check it:

goozels --help

Set up your editor

Pick your editor — each guide is a couple of lines of config:

Editor	Guide
VS Code	editors/vscode/README.md — easiest: add "go.alternateTools": { "gopls": "goozels" } to settings
Neovim	editors/neovim.md
GoLand / IntelliJ	editors/jetbrains.md
Other LSP editors	Launch goozels over stdio wherever you'd launch gopls, and also attach it to gooze.yaml files.

goozels replaces gopls in your editor (it runs gopls for you behind the scenes). You don't need to configure gopls separately, and you shouldn't run both for the same files.

Try it

Open the examples in testdata/:

• testdata/example.go — put your cursor after //gooze:ignore and trigger completion; hover the mutagen names; notice the warning on the intentionally-wrong bogus.
• testdata/gooze.yaml — add a new key and let it complete; change log.level to something invalid and watch it get flagged.

Options

goozels needs no configuration, but you can point it at specific binaries:

Flag	Environment variable	Default	Purpose
--gopls PATH	GOOZELS_GOPLS	gopls on PATH	The Go language server to run behind goozels
--gooze PATH	GOOZELS_GOOZE	gooze on PATH	The gooze binary used by the run / list buttons

Troubleshooting

• No Go features at all — goozels couldn't start gopls. Make sure gopls is installed and on your PATH, or set GOOZELS_GOPLS to its full path.
• The ▶ run / list buttons do nothing / error — gooze isn't installed or on your PATH. Install it (see Requirements) or set GOOZELS_GOOZE.
• No report scores appear — run mutation testing first (the ▶ gooze run button or gooze run ./...). goozels reads the .gooze-reports/ directory in your workspace root. The per-line "surviving mutant" markers are approximate: gooze doesn't record exact line positions in its reports, so the file-level score is exact but the in-line markers are a best-effort hint.
• Doubled completions in GoLand — GoLand has its own Go engine, so it shows both. See the note in the JetBrains guide.
• goozels: command not found — your Go bin directory isn't on PATH. Add export PATH="$PATH:$(go env GOPATH)/bin" to your shell profile.

License

MIT.

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Contributing or curious how it works? See CONTRIBUTING.md.