/go-packages

name: go-packages
description: Use when creating Go packages, organizing imports, managing dependencies, or deciding how to structure Go code into packages. Also use when starting a new Go project or splitting a growing codebase into packages, even if the user doesn't explicitly ask about package organization. Does not cover naming individual identifiers (see go-naming).

Go Packages and Imports

Resource Routing

• `references/IMPORTS.md` - Read when grouping imports, using blank imports, dot imports, or import aliases.
• `references/PACKAGE-SIZE.md` - Read when splitting packages, avoiding `init`, structuring `main`, or designing CLI flags/subcommands.

> **When this skill does NOT apply**: For naming individual identifiers within a package, see [go-naming](../go-naming/SKILL.md). For organizing functions within a single file, see [go-functions](../go-functions/SKILL.md). For configuring linters that enforce import rules, see [go-linting](../go-linting/SKILL.md).

Package Organization

Avoid Util Packages

Package names should describe what the package provides. Avoid generic names like `util`, `helper`, `common` — they obscure meaning and cause import conflicts.

// Good: Meaningful package names
db := spannertest.NewDatabaseFromFile(...)
_, err := f.Seek(0, io.SeekStart)

// Bad: Vague names obscure meaning
db := test.NewDatabaseFromFile(...)
_, err := f.Seek(0, common.SeekStart)

Generic names can be used as *part* of a name (e.g., `stringutil`) but should not be the entire package name.

Package Size

| Question | Action | |----------|--------| | Can you describe its purpose in one sentence? | No → split by responsibility | | Do files never share unexported symbols? | Those files could be separate packages | | Distinct user groups use different parts? | Split along user boundaries | | Godoc page overwhelming? | Split to improve discoverability |

**Do NOT split** just because a file is long, to create single-type packages, or if it would create circular dependencies.

---

Imports

Imports are organized in groups separated by blank lines. Standard library packages always come first. Use [goimports](https://pkg.go.dev/golang.org/x/tools/cmd/goimports) to manage this automatically.

import (
    "fmt"
    "os"

    "github.com/foo/bar"
    "rsc.io/goversion/version"
)

**Quick rules:**

| Rule | Guidance | |------|----------| | Grouping | stdlib first, then external. Extended: stdlib → other → protos → side-effects | | Renaming | Avoid unless collision. Rename the most local import. Proto packages get `pb` suffix | | Blank imports (`import _`) | Only in `main` packages or tests | | Dot imports (`import .`) | Never use, except for circular-dependency test files |

---

Avoid init()

Avoid `init()` where possible. When unavoidable, it must be:

1. Completely deterministic 2. Independent of other `init()` ordering 3. Free of environment state (env vars, working dir, args) 4. Free of I/O (filesystem, network, system calls)

**Acceptable uses**: complex expressions that can't be single assignments, pluggable hooks (e.g., `database/sql` dialects), deterministic precomputation.

---

Exit in Main

Call `os.Exit` or `log.Fatal*` **only in `main()`**. All other functions should return errors.

**Why**: Non-obvious control flow, untestable, `defer` statements skipped.

**Best practice**: Use the `run()` pattern — extract logic into `func run() error`, call from `main()` with a single exit point:

func main() {
    if err := run(); err != nil {
        log.Fatal(err)
    }
}

---

Command-Line Flags

> **Advisory**: Define flags only in `package main`.

• Flag names use `snake_case`: `--output_dir` not `--outputDir`
• Libraries should accept configuration as parameters, not read flags directly —

this keeps them testable and reusable

• Prefer the standard `flag` package; use `pflag` only when POSIX conventions

(double-dash, single-char shortcuts) are required

// Good: Flag in main, passed as parameter to library
func main() {
    outputDir := flag.String("output_dir", ".", "directory for output files")
    flag.Parse()
    if err := mylib.Generate(*outputDir); err != nil {
        log.Fatal(err)
    }
}

---

Related Skills

• **Package naming**: See [go-naming](../go-naming/SKILL.md) when choosing package names, avoiding stuttering, or naming exported symbols
• **Error handling across packages**: See [go-error-handling](../go-error-handling/SKILL.md) when wrapping errors at package boundaries with `%w` vs `%v`
• **Import linting**: See [go-linting](../go-linting/SKILL.md) when configuring goimports local-prefixes or enforcing import grouping
• **Global state**: See [go-defensive](../go-defensive/SKILL.md) when replacing `init()` with explicit initialization or avoiding mutable globals