nix: make System, Version, SourceProfile public

As part of some cleanup for making the DetSys installer the default,
move the code related to getting the Nix version and system to the
non-internal go.jetpack.io/devbox/nix package. It also merges in some
nearly-duplicate code from the search indexer's Nix code (which will
eventually use this package instead).

Some of the changes taken from the indexer are:

- Calling any function or method automatically...
	- sources the Nix profile if necessary.
	- looks for Nix in some well-known places if it isn't in PATH.
- `nix.Version` and `nix.System` are cached behind a `sync.Once` by
  default.

All top-level functions map to a method on a default Nix struct,
following the same pattern found in `flags`, `slog`, etc.

	const Version2_12 = "2.12.0" ...
	func AtLeast(version string) bool
	func SourceProfile() (sourced bool, err error)
	func System() string
	func Version() string
	type Info struct{ ... }
	type Nix struct{ ... }
	    func Default() *Nix
	    func LookPath() *Nix
	    func (n *Nix) Info() (Info, error)
	    func (n *Nix) System() string
	    func (n *Nix) Version() string

Author: gcurtis

internal/devbox/devbox.go

@@ -115,7 +115,7 @@ func Open(opts *devopt.Opts) (*Devbox, error) {
 		cfg:                      cfg,
 		env:                      opts.Env,
 		environment:              environment,
-		nix:                      &nix.Nix{},
+		nix:                      &nix.NixInstance{},
 		projectDir:               filepath.Dir(cfg.Root.AbsRootPath),
 		pluginManager:            plugin.NewManager(),
 		stderr:                   opts.Stderr,

internal/devpkg/narinfo_cache.go

@@ -18,6 +18,7 @@ import (
 	"go.jetpack.io/devbox/internal/goutil"
 	"go.jetpack.io/devbox/internal/lock"
 	"go.jetpack.io/devbox/internal/nix"
+	"go.jetpack.io/devbox/internal/redact"
 	"golang.org/x/sync/errgroup"
 )
 
@@ -73,14 +74,6 @@ func FillNarInfoCache(ctx context.Context, packages ...*Package) error {
 		return nil
 	}
 
-	// Pre-compute values read in fillNarInfoCache
-	// so they can be read from multiple go-routines without locks
-	_, err := nix.Version()
-	if err != nil {
-		return err
-	}
-	_ = nix.System()
-
 	group, _ := errgroup.WithContext(ctx)
 	for _, p := range eligiblePackages {
 		pkg := p // copy the loop variable since its used in a closure below
@@ -240,29 +233,23 @@ func (p *Package) sysInfoIfExists() (*lock.SystemInfo, error) {
 		return nil, nil
 	}
 
-	version, err := nix.Version()
-	if err != nil {
-		return nil, err
-	}
-
 	// disable for nix < 2.17
-	if !version.AtLeast(nix.Version2_17) {
-		return nil, err
+	minVersion := nix.Version2_17
+	if !nix.AtLeast(minVersion) {
+		return nil, redact.Errorf("nix version is older than %s", redact.Safe(minVersion))
 	}
 
 	entry, err := p.lockfile.Resolve(p.Raw)
 	if err != nil {
 		return nil, err
 	}
 
-	userSystem := nix.System()
-
 	if entry.Systems == nil {
 		return nil, nil
 	}
 
 	// Check if the user's system's info is present in the lockfile
-	sysInfo, ok := entry.Systems[userSystem]
+	sysInfo, ok := entry.Systems[nix.System()]
 	if !ok {
 		return nil, nil
 	}

internal/devpkg/package.go

@@ -390,7 +390,7 @@ func (p *Package) normalizePackageAttributePath() (string, error) {
 
 	// We prefer nix.Search over just trying to parse the package's "URL" because
 	// nix.Search will guarantee that the package exists for the current system.
-	var infos map[string]*nix.Info
+	var infos map[string]*nix.PkgInfo
 	if p.IsDevboxPackage && !p.IsRunX() {
 		// Perf optimization: For queries of the form nixpkgs/<commit>#foo, we can
 		// use a nix.Search cache.

internal/nix/config.go

@@ -16,6 +16,7 @@ import (
 	"strings"
 
 	"go.jetpack.io/devbox/internal/redact"
+	"go.jetpack.io/devbox/nix"
 )
 
 // Config is a parsed Nix configuration.
@@ -106,7 +107,7 @@ func (c Config) IsUserTrusted(ctx context.Context, username string) (bool, error
 }
 
 func IncludeDevboxConfig(ctx context.Context, username string) error {
-	info, _ := versionInfo()
+	info, _ := nix.Default().Info()
 	path := cmp.Or(info.SystemConfig, "/etc/nix/nix.conf")
 	includePath := filepath.Join(filepath.Dir(path), "devbox-nix.conf")
 	b := fmt.Appendf(nil, "# This config was auto-generated by Devbox.\n\nextra-trusted-users = %s\n", username)

internal/nix/install.go

@@ -21,8 +21,8 @@ import (
 	"go.jetpack.io/devbox/internal/build"
 	"go.jetpack.io/devbox/internal/cmdutil"
 	"go.jetpack.io/devbox/internal/fileutil"
-	"go.jetpack.io/devbox/internal/redact"
 	"go.jetpack.io/devbox/internal/ux"
+	"go.jetpack.io/devbox/nix"
 )
 
 const rootError = "warning: installing Nix as root is not supported by this script!"
@@ -121,33 +121,23 @@ func EnsureNixInstalled(writer io.Writer, withDaemonFunc func() *bool) (err erro
 			return
 		}
 
-		var version VersionInfo
-		version, err = Version()
-		if err != nil {
-			err = redact.Errorf("nix: ensure install: get version: %w", err)
-			return
-		}
-
 		// ensure minimum nix version installed
-		if !version.AtLeast(MinVersion) {
+		if !nix.AtLeast(MinVersion) {
 			err = usererr.New(
 				"Devbox requires nix of version >= %s. Your version is %s. "+
 					"Please upgrade nix and try again.\n",
 				MinVersion,
-				version,
+				nix.Version(),
 			)
 			return
 		}
-		// call ComputeSystem to ensure its value is internally cached so other
-		// callers can rely on just calling System
-		err = ComputeSystem()
 	}()
 
 	if BinaryInstalled() {
 		return nil
 	}
 	if dirExists() {
-		if err = SourceNixEnv(); err != nil {
+		if _, err = SourceProfile(); err != nil {
 			return err
 		} else if BinaryInstalled() {
 			return nil
@@ -174,7 +164,7 @@ func EnsureNixInstalled(writer io.Writer, withDaemonFunc func() *bool) (err erro
 	}
 
 	// Source again
-	if err = SourceNixEnv(); err != nil {
+	if _, err = SourceProfile(); err != nil {
 		return err
 	}
 

internal/nix/instance.go

@@ -6,7 +6,7 @@ package nix
 import "context"
 
 // These make it easier to stub out nix for testing
-type Nix struct{}
+type NixInstance struct{}
 
 type Nixer interface {
 	PrintDevEnv(ctx context.Context, args *PrintDevEnvArgs) (*PrintDevEnvOut, error)