Add back internal caching for previously generated packages

generate/generate.go

@@ -8,6 +8,7 @@ import (
 	"io/ioutil"
 	"os/exec"
 	"path"
+	"sort"
 	"strings"
 	"sync"
 
@@ -79,17 +80,30 @@ func GeneratePkgs(goModPath string, goMod2NixPath string, numWorkers int) ([]*sc
 	executor := lib.NewParallellExecutor(numWorkers)
 	var mux sync.Mutex
 
+	cache := schema.ReadCache(goMod2NixPath)
+
 	packages := []*schema.Package{}
+	addPkg := func(pkg *schema.Package) {
+		mux.Lock()
+		packages = append(packages, pkg)
+		mux.Unlock()
+	}
+
 	for _, dl := range modDownloads {
 		dl := dl
 
+		goPackagePath, hasReplace := replace[dl.Path]
+		if !hasReplace {
+			goPackagePath = dl.Path
+		}
+
+		cached, ok := cache[goPackagePath]
+		if ok && cached.Version == dl.Version {
+			addPkg(cached)
+			continue
+		}
+
 		executor.Add(func() error {
-
-			goPackagePath, hasReplace := replace[dl.Path]
-			if !hasReplace {
-				goPackagePath = dl.Path
-			}
-
 			var storePath string
 			{
 				stdout, err := exec.Command(
@@ -119,9 +133,7 @@ func GeneratePkgs(goModPath string, goMod2NixPath string, numWorkers int) ([]*sc
 				pkg.ReplacedPath = dl.Path
 			}
 
-			mux.Lock()
+			addPkg(pkg)
-			packages = append(packages, pkg)
-			mux.Unlock()
 
 			return nil
 		})
@@ -132,6 +144,10 @@ func GeneratePkgs(goModPath string, goMod2NixPath string, numWorkers int) ([]*sc
 		return nil, err
 	}
 
+	sort.Slice(packages, func(i, j int) bool {
+		return packages[i].GoPackagePath < packages[j].GoPackagePath
+	})
+
 	return packages, nil
 
 }

schema/schema.go

@@ -3,6 +3,7 @@ package types
 import (
 	"bytes"
 	"github.com/BurntSushi/toml"
+	"os"
 )
 
 const SchemaVersion = 1
@@ -38,3 +39,33 @@ func Marshal(pkgs []*Package) ([]byte, error) {
 
 	return buf.Bytes(), nil
 }
+
+func ReadCache(filePath string) map[string]*Package {
+	ret := make(map[string]*Package)
+
+	if filePath == "" {
+		return ret
+	}
+
+	b, err := os.ReadFile(filePath)
+	if err != nil {
+		return ret
+	}
+
+	var output Output
+	_, err = toml.Decode(string(b), &output)
+	if err != nil {
+		return ret
+	}
+
+	if output.SchemaVersion != SchemaVersion {
+		return ret
+	}
+
+	for k, v := range output.Mod {
+		v.GoPackagePath = k
+		ret[k] = v
+	}
+
+	return ret
+}