Replace dependency on Nix with go-nix

This calculates the output hashes in pure Go and removes Nix from
being a run time dependency of gomod2nix.

Additionally it should be faster, but that's untested.

generate/generate.go

@@ -2,16 +2,16 @@ package fetch
 
 import (
 	"bytes"
+	"crypto/sha256"
+	"encoding/base64"
 	"encoding/json"
-	"fmt"
 	"io"
 	"io/ioutil"
 	"os/exec"
-	"path"
 	"sort"
-	"strings"
 	"sync"
 
+	"github.com/nix-community/go-nix/pkg/nar"
 	log "github.com/sirupsen/logrus"
 	"github.com/tweag/gomod2nix/lib"
 	schema "github.com/tweag/gomod2nix/schema"
@@ -77,7 +77,7 @@ func GeneratePkgs(goModPath string, goMod2NixPath string, numWorkers int) ([]*sc
 		log.Info("Done downloading dependencies")
 	}
 
-	executor := lib.NewParallellExecutor(numWorkers)
+	executor := lib.NewParallellExecutor()
 	var mux sync.Mutex
 
 	cache := schema.ReadCache(goMod2NixPath)
@@ -104,30 +104,17 @@ func GeneratePkgs(goModPath string, goMod2NixPath string, numWorkers int) ([]*sc
 		}
 
 		executor.Add(func() error {
-			var storePath string
+			h := sha256.New()
-			{
+			err := nar.DumpPath(h, dl.Dir)
-				stdout, err := exec.Command(
-					"nix", "eval", "--impure", "--expr",
-					fmt.Sprintf("builtins.path { name = \"%s_%s\"; path = \"%s\"; }", path.Base(goPackagePath), dl.Version, dl.Dir),
-				).Output()
-				if err != nil {
-					return err
-				}
-				storePath = string(stdout)[1 : len(stdout)-2]
-			}
-
-			stdout, err := exec.Command(
-				"nix-store", "--query", "--hash", storePath,
-			).Output()
 			if err != nil {
 				return err
 			}
-			hash := strings.TrimSpace(string(stdout))
+			digest := h.Sum(nil)
 
 			pkg := &schema.Package{
 				GoPackagePath: goPackagePath,
 				Version:       dl.Version,
-				Hash:          hash,
+				Hash:          "sha256-" + base64.StdEncoding.EncodeToString(digest),
 			}
 			if hasReplace {
 				pkg.ReplacedPath = dl.Path

go.mod

@@ -4,6 +4,7 @@ go 1.14
 
 require (
 	github.com/BurntSushi/toml v0.3.1
+	github.com/nix-community/go-nix v0.0.0-20220528121639-b940fb0a12d8
 	github.com/sirupsen/logrus v1.7.0
 	golang.org/x/mod v0.3.0
 	golang.org/x/sys v0.0.0-20220519141025-dcacdad47464 // indirect

go.sum

@@ -1,13 +1,30 @@
 github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/alecthomas/kong v0.5.0/go.mod h1:uzxf/HUh0tj43x1AyJROl3JT7SgsZ5m+icOv1csRhc0=
+github.com/alecthomas/participle/v2 v2.0.0-alpha7/go.mod h1:NumScqsC42o9x+dGj8/YqsIfhrIQjFEOFovxotbBirA=
+github.com/alecthomas/repr v0.0.0-20181024024818-d37bc2a10ba1/go.mod h1:xTS7Pm1pD1mvyM075QCDSRqH6qRLXylzS24ZTpRiSzQ=
+github.com/alecthomas/repr v0.0.0-20210801044451-80ca428c5142/go.mod h1:2kn6fqh/zIyPLmm3ugklbEi5hg5wS435eygvNfaDQL8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/nix-community/go-nix v0.0.0-20220528121639-b940fb0a12d8 h1:IYr+3pldQtTwS55Xm2+3Ry81MpSKNVpMyYMNr7yQpts=
+github.com/nix-community/go-nix v0.0.0-20220528121639-b940fb0a12d8/go.mod h1:r5pCQAjHNSDWTsy6+UbacPN8EzMVJiCAXDWbRN2qfwU=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sirupsen/logrus v1.7.0 h1:ShrD1U9pZB12TX0cVy0DtePoCH97K8EtX+mg7ZARUtM=
 github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
-github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/mod v0.3.0 h1:RM4zey1++hCTbCVQfnWeKs9/IEsaBLA8vTkd0WVtmH4=
@@ -23,5 +40,13 @@ golang.org/x/sys v0.0.0-20220519141025-dcacdad47464/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898 h1:/atklqdjdhuosWIl6AIbOeHJjicWYPqR9bpxqxYG2pA=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

lib/executor.go

@@ -9,19 +9,17 @@ type ParallellExecutor struct {
 	errChan chan error
 	wg      *sync.WaitGroup
 	mux     *sync.Mutex
-	guard   chan struct{}
 
 	// Error returned by Wait(), cached for other Wait() invocations
 	err  error
 	done bool
 }
 
-func NewParallellExecutor(maxWorkers int) *ParallellExecutor {
+func NewParallellExecutor() *ParallellExecutor {
 	return &ParallellExecutor{
 		errChan: make(chan error),
 		mux:     new(sync.Mutex),
 		wg:      new(sync.WaitGroup),
-		guard:   make(chan struct{}, maxWorkers),
 
 		err:  nil,
 		done: false,
@@ -31,13 +29,8 @@ func NewParallellExecutor(maxWorkers int) *ParallellExecutor {
 func (e *ParallellExecutor) Add(fn func() error) {
 	e.wg.Add(1)
 
-	e.guard <- struct{}{} // Block
-
 	go func() {
 		defer e.wg.Done()
-		defer func() {
-			<-e.guard
-		}()
 
 		err := fn()
 		if err != nil {