Improve performance of mock generation (#397)

Optimizes resolving correct package name with `go list` command. Instead of calling go list for each import in file, now we do it for all imports in one call.

mockgen/mockgen.go

@@ -304,10 +304,12 @@ func (g *generator) Generate(pkg *model.Package, outputPkgName string, outputPac
 	}
 	sort.Strings(sortedPaths)
 
+	packagesName := createPackageMap(sortedPaths)
+
 	g.packageMap = make(map[string]string, len(im))
 	localNames := make(map[string]bool, len(im))
 	for _, pth := range sortedPaths {
-		base, ok := lookupPackageName(pth)
+		base, ok := packagesName[pth]
 		if !ok {
 			base = sanitize(path.Base(pth))
 		}
@@ -622,22 +624,30 @@ func (g *generator) Output() []byte {
 	return src
 }
 
-func lookupPackageName(importPath string) (string, bool) {
+// createPackageMap returns a map of import path to package name
+// for specified importPaths.
+func createPackageMap(importPaths []string) map[string]string {
 	var pkg struct {
-		Name string
+		Name       string
+		ImportPath string
 	}
+	pkgMap := make(map[string]string)
 	b := bytes.NewBuffer(nil)
-	cmd := exec.Command("go", "list", "-json", importPath)
+	args := []string{"list", "-json"}
+	args = append(args, importPaths...)
+	cmd := exec.Command("go", args...)
 	cmd.Stdout = b
-	err := cmd.Run()
-	if err != nil {
-		return "", false
-	}
-	err = json.Unmarshal(b.Bytes(), &pkg)
-	if err != nil {
-		return "", false
+	cmd.Run()
+	dec := json.NewDecoder(b)
+	for dec.More() {
+		err := dec.Decode(&pkg)
+		if err != nil {
+			log.Printf("failed to decode 'go list' output: %v", err)
+			continue
+		}
+		pkgMap[pkg.ImportPath] = pkg.Name
 	}
-	return pkg.Name, true
+	return pkgMap
 }
 
 func printVersion() {

mockgen/mockgen_test.go

@@ -335,10 +335,7 @@ func TestGetArgNames(t *testing.T) {
 	}
 }
 
-func Test_lookupPackageName(t *testing.T) {
-	type args struct {
-		importPath string
-	}
+func Test_createPackageMap(t *testing.T) {
 	tests := []struct {
 		name            string
 		importPath      string
@@ -350,14 +347,19 @@ func Test_lookupPackageName(t *testing.T) {
 		{"modules", "rsc.io/quote/v3", "quote", true},
 		{"fail", "this/should/not/work", "", false},
 	}
+	var importPaths []string
+	for _, t := range tests {
+		importPaths = append(importPaths, t.importPath)
+	}
+	packages := createPackageMap(importPaths)
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			gotPackageName, gotOk := lookupPackageName(tt.importPath)
+			gotPackageName, gotOk := packages[tt.importPath]
 			if gotPackageName != tt.wantPackageName {
-				t.Errorf("lookupPackageName() gotPackageName = %v, wantPackageName %v", gotPackageName, tt.wantPackageName)
+				t.Errorf("createPackageMap() gotPackageName = %v, wantPackageName = %v", gotPackageName, tt.wantPackageName)
 			}
 			if gotOk != tt.wantOK {
-				t.Errorf("lookupPackageName() gotOk = %v, wantOK %v", gotOk, tt.wantOK)
+				t.Errorf("createPackageMap() gotOk = %v, wantOK = %v", gotOk, tt.wantOK)
 			}
 		})
 	}

mockgen/parse.go

@@ -432,6 +432,15 @@ func (p *fileParser) parseType(pkg string, typ ast.Expr) (model.Type, error) {
 // importsOfFile returns a map of package name to import path
 // of the imports in file.
 func importsOfFile(file *ast.File) (normalImports map[string]string, dotImports []string) {
+	var importPaths []string
+	for _, is := range file.Imports {
+		if is.Name != nil {
+			continue
+		}
+		importPath := is.Path.Value[1 : len(is.Path.Value)-1] // remove quotes
+		importPaths = append(importPaths, importPath)
+	}
+	packagesName := createPackageMap(importPaths)
 	normalImports = make(map[string]string)
 	dotImports = make([]string, 0)
 	for _, is := range file.Imports {
@@ -445,7 +454,7 @@ func importsOfFile(file *ast.File) (normalImports map[string]string, dotImports
 			}
 			pkgName = is.Name.Name
 		} else {
-			pkg, ok := lookupPackageName(importPath)
+			pkg, ok := packagesName[importPath]
 			if !ok {
 				// Fallback to import path suffix. Note that this is uncertain.
 				_, last := path.Split(importPath)