use-modern-go

Modern Go Guidelines

Detected Go Version

!grep -rh "^go " --include="go.mod" . 2>/dev/null | cut -d' ' -f2 | sort | uniq -c | sort -nr | head -1 | xargs | cut -d' ' -f2 | grep . || echo unknown

How to Use This Skill

DO NOT search for go.mod files or try to detect the version yourself. Use ONLY the version shown above.

If version detected (not "unknown"):

• Say: "This project is using Go X.XX, so I’ll stick to modern Go best practices and freely use language features up to and including this version. If you’d prefer a different target version, just let me know."
• Do NOT list features, do NOT ask for confirmation

If version is "unknown":

• Say: "Could not detect Go version in this repository"
• Use AskUserQuestion: "Which Go version should I target?" → [1.23] / [1.24] / [1.25] / [1.26]

When writing Go code, use ALL features from this document up to the target version:

• Prefer modern built-ins and packages (slices, maps, cmp) over legacy patterns
• Never use features from newer Go versions than the target
• Never use outdated patterns when a modern alternative is available

When modernizing existing Go files, if the installed toolchain is Go 1.26 or newer, run go fix on the target package(s) before reading any file.

go version                            # gate on the installed toolchain

go fix -diff ./path/to/pkg/...        # preview (the unflagged form writes files in place)
go fix ./path/to/pkg/...              # apply
go fix ./path/to/pkg/...              # run a second pass; one fix often enables another

go build ./path/to/pkg/...            # verify nothing broke
go test ./path/to/pkg/...

Then read the post-fix files and apply manual modernizations from the Features list for anything go fix did not catch. Do not Read a Go file you plan to modernize until go fix has run on its package, otherwise you will end up doing work the tool would have done for free.

Caveats:

• go fix only applies a fix when the file's or module's declared Go version permits the target feature (go 1.X in go.mod or //go:build go1.X in the file).
• Generated files (per //go:generate) are skipped. Fix the generator instead.
• Each run analyzes one build configuration. For code with GOOS/GOARCH build tags, re-run per combo (e.g. GOOS=linux GOARCH=amd64 go fix ./..., then GOOS=darwin GOARCH=arm64 go fix ./...).
• The tool resolves syntactic conflicts but can leave semantic ones (e.g. now-unused variables). Compilation errors after go fix are normal and require manual resolution.
• go tool fix help lists the available fixers; -name=false disables a specific one (e.g. go fix -minmax=false ./...).