nix: make System, Version, SourceProfile public (#2443)

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" ...
	var Default = &Nix{}
	func AtLeast(version string) bool
	func SourceProfile() (sourced bool, err error)
	func System() string
	func Version() string
	type Info struct{ ... }
		func (i Info) AtLeast(version string) bool
	type Nix struct{ ... }
		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

@@ -73,14 +73,6 @@ 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 +232,22 @@ 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
+	if !nix.AtLeast(nix.Version2_17) {
+		return nil, nil
 	}
 
 	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)

internal/nix/nix.go

@@ -16,15 +16,13 @@ import (
 	"runtime"
 	"runtime/trace"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/pkg/errors"
 	"go.jetpack.io/devbox/internal/boxcli/featureflag"
 	"go.jetpack.io/devbox/internal/boxcli/usererr"
 	"go.jetpack.io/devbox/internal/redact"
 	"go.jetpack.io/devbox/nix/flake"
-	"golang.org/x/mod/semver"
 
 	"go.jetpack.io/devbox/internal/debug"
 )
@@ -51,7 +49,7 @@ type PrintDevEnvArgs struct {
 
 // PrintDevEnv calls `nix print-dev-env -f <path>` and returns its output. The output contains
 // all the environment variables and bash functions required to create a nix shell.
-func (*Nix) PrintDevEnv(ctx context.Context, args *PrintDevEnvArgs) (*PrintDevEnvOut, error) {
+func (*NixInstance) PrintDevEnv(ctx context.Context, args *PrintDevEnvArgs) (*PrintDevEnvOut, error) {
 	defer debug.FunctionTimer().End()
 	defer trace.StartRegion(ctx, "nixPrintDevEnv").End()
 
@@ -128,226 +126,10 @@ func ExperimentalFlags() []string {
 	}
 }
 
-func System() string {
-	if cachedSystem == "" {
-		// While this should have been initialized, we do a best-effort to avoid
-		// a panic.
-		if err := ComputeSystem(); err != nil {
-			panic(fmt.Sprintf(
-				"System called before being initialized by ComputeSystem: %v",
-				err,
-			))
-		}
-	}
-	return cachedSystem
-}
-
-var cachedSystem string
-
-func ComputeSystem() error {
-	// For Savil to debug "remove nixpkgs" feature. The Search api lacks x86-darwin info.
-	// So, I need to fake that I am x86-linux and inspect the output in generated devbox.lock
-	// and flake.nix files.
-	// This is also used by unit tests.
-	if cachedSystem != "" {
-		return nil
-	}
-	override := os.Getenv("__DEVBOX_NIX_SYSTEM")
-	if override != "" {
-		cachedSystem = override
-	} else {
-		cmd := command("eval", "--impure", "--raw", "--expr", "builtins.currentSystem")
-		out, err := cmd.Output(context.TODO())
-		if err != nil {
-			return err
-		}
-		cachedSystem = string(out)
-	}
-	return nil
-}
-
 func SystemIsLinux() bool {
 	return strings.Contains(System(), "linux")
 }
 
-// All major Nix versions supported by Devbox.
-const (
-	Version2_12 = "2.12.0"
-	Version2_13 = "2.13.0"
-	Version2_14 = "2.14.0"
-	Version2_15 = "2.15.0"
-	Version2_16 = "2.16.0"
-	Version2_17 = "2.17.0"
-	Version2_18 = "2.18.0"
-	Version2_19 = "2.19.0"
-	Version2_20 = "2.20.0"
-	Version2_21 = "2.21.0"
-	Version2_22 = "2.22.0"
-
-	MinVersion = Version2_12
-)
-
-// versionRegexp matches the first line of "nix --version" output.
-//
-// The semantic component is sourced from <https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string>.
-// It's been modified to tolerate Nix prerelease versions, which don't have a
-// hyphen before the prerelease component and contain underscores.
-var versionRegexp = regexp.MustCompile(`^(.+) \(.+\) ((?P<major>0|[1-9]\d*)\.(?P<minor>0|[1-9]\d*)\.(?P<patch>0|[1-9]\d*)(?:(?:-|pre)(?P<prerelease>(?:0|[1-9]\d*|\d*[_a-zA-Z-][_0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[_a-zA-Z-][_0-9a-zA-Z-]*))*))?(?:\+(?P<buildmetadata>[0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?)$`)
-
-// preReleaseRegexp matches Nix prerelease version strings, which are not valid
-// semvers.
-var preReleaseRegexp = regexp.MustCompile(`pre(?P<date>[0-9]+)_(?P<commit>[a-f0-9]{4,40})$`)
-
-// VersionInfo contains information about a Nix installation.
-type VersionInfo struct {
-	// Name is the executed program name (the first element of argv).
-	Name string
-
-	// Version is the semantic Nix version string.
-	Version string
-
-	// System is the current Nix system. It follows the pattern <arch>-<os>
-	// and does not use the same values as GOOS or GOARCH.
-	System string
-
-	// ExtraSystems are other systems that the current machine supports.
-	// Usually set by the extra-platforms setting in nix.conf.
-	ExtraSystems []string
-
-	// Features are the capabilities that the Nix binary was compiled with.
-	Features []string
-
-	// SystemConfig is the path to the Nix system configuration file,
-	// usually /etc/nix/nix.conf.
-	SystemConfig string
-
-	// UserConfigs is a list of paths to the user's Nix configuration files.
-	UserConfigs []string
-
-	// StoreDir is the path to the Nix store directory, usually /nix/store.
-	StoreDir string
-
-	// StateDir is the path to the Nix state directory, usually
-	// /nix/var/nix.
-	StateDir string
-
-	// DataDir is the path to the Nix data directory, usually somewhere
-	// within the Nix store. This field is empty for Nix versions <= 2.12.
-	DataDir string
-}
-
-func parseVersionInfo(data []byte) (VersionInfo, error) {
-	// Example nix --version --debug output from Nix versions 2.12 to 2.21.
-	// Version 2.12 omits the data directory, but they're otherwise
-	// identical.
-	//
-	// See https://github.com/NixOS/nix/blob/5b9cb8b3722b85191ee8cce8f0993170e0fc234c/src/libmain/shared.cc#L284-L305
-	//
-	// nix (Nix) 2.21.2
-	// System type: aarch64-darwin
-	// Additional system types: x86_64-darwin
-	// Features: gc, signed-caches
-	// System configuration file: /etc/nix/nix.conf
-	// User configuration files: /Users/nobody/.config/nix/nix.conf:/etc/xdg/nix/nix.conf
-	// Store directory: /nix/store
-	// State directory: /nix/var/nix
-	// Data directory: /nix/store/m0ns07v8by0458yp6k30rfq1rs3kaz6g-nix-2.21.2/share
-
-	info := VersionInfo{}
-	if len(data) == 0 {
-		return info, redact.Errorf("empty nix --version output")
-	}
-
-	lines := strings.Split(string(data), "\n")
-	matches := versionRegexp.FindStringSubmatch(lines[0])
-	if len(matches) < 3 {
-		return info, redact.Errorf("parse nix version: %s", redact.Safe(lines[0]))
-	}
-	info.Name = matches[1]
-	info.Version = matches[2]
-	for _, line := range lines {
-		name, value, found := strings.Cut(line, ": ")
-		if !found {
-			continue
-		}
-
-		switch name {
-		case "System type":
-			info.System = value
-		case "Additional system types":
-			info.ExtraSystems = strings.Split(value, ", ")
-		case "Features":
-			info.Features = strings.Split(value, ", ")
-		case "System configuration file":
-			info.SystemConfig = value
-		case "User configuration files":
-			info.UserConfigs = strings.Split(value, ":")
-		case "Store directory":
-			info.StoreDir = value
-		case "State directory":
-			info.StateDir = value
-		case "Data directory":
-			info.DataDir = value
-		}
-	}
-	return info, nil
-}
-
-// AtLeast returns true if v.Version is >= version per semantic versioning. It
-// always returns false if v.Version is empty or invalid, such as when the
-// current Nix version cannot be parsed. It panics if version is an invalid
-// semver.
-func (v VersionInfo) AtLeast(version string) bool {
-	if !strings.HasPrefix(version, "v") {
-		version = "v" + version
-	}
-	if !semver.IsValid(version) {
-		panic(fmt.Sprintf("nix.atLeast: invalid version %q", version[1:]))
-	}
-	if semver.IsValid("v" + v.Version) {
-		return semver.Compare("v"+v.Version, version) >= 0
-	}
-
-	// If the version isn't a valid semver, check to see if it's a
-	// prerelease (e.g., 2.23.0pre20240526_7de033d6) and coerce it to a
-	// valid version (2.23.0-pre.20240526+7de033d6) so we can compare it.
-	prerelease := preReleaseRegexp.ReplaceAllString(v.Version, "-pre.$date+$commit")
-	return semver.Compare("v"+prerelease, version) >= 0
-}
-
-// version is the cached output of `nix --version --debug`.
-var versionInfo = sync.OnceValues(runNixVersion)
-
-func runNixVersion() (VersionInfo, error) {
-	// Arbitrary timeout to make sure we don't take too long or hang.
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-
-	// Intentionally don't use the nix.command function here. We use this to
-	// perform Nix version checks and don't want to pass any extra-features
-	// or flags that might be missing from old versions.
-	cmd := exec.CommandContext(ctx, "nix", "--version", "--debug")
-	out, err := cmd.Output()
-	if err != nil {
-		var exitErr *exec.ExitError
-		if errors.As(err, &exitErr) && len(exitErr.Stderr) != 0 {
-			return VersionInfo{}, redact.Errorf("nix command: %s: %q: %v", redact.Safe(cmd), exitErr.Stderr, err)
-		}
-		if errors.Is(ctx.Err(), context.DeadlineExceeded) {
-			return VersionInfo{}, redact.Errorf("nix command: %s: timed out while reading output: %v", redact.Safe(cmd), err)
-		}
-		return VersionInfo{}, redact.Errorf("nix command: %s: %v", redact.Safe(cmd), err)
-	}
-
-	slog.Debug("nix --version --debug output", "out", out)
-	return parseVersionInfo(out)
-}
-
-// Version returns the currently installed version of Nix.
-func Version() (VersionInfo, error) {
-	return versionInfo()
-}
-
 var nixPlatforms = []string{
 	"aarch64-darwin",
 	"aarch64-linux",