Filter out main modules (#17)

This fixes an issue with multi-module projects that accidentially
vendored main modules, causing already-exists errors when symlinking.

The same strategy is employed by go in the `go mod vendor` command, see
https://github.com/golang/go/blob/81efd7b347dd6d7f12fd49c6eee0274005734c71/src/cmd/go/internal/modcmd/vendor.go#L100

internal/internal.go

@@ -105,8 +105,10 @@ func BuildModuleNodes(modules []Module) ([]Node, error) {
 }
 
 type Module struct {
-	Path string
-	Dir  string
+	Path    string
+	Dir     string
+	Version string
+	Main    bool
 }
 
 type moduleReader struct {
@@ -181,10 +183,6 @@ func ParseModules(r io.Reader) ([]Module, error) {
 			return nil, err
 		}
 
-		// Don't include indirect modules without directory.
-		if mod.Dir == "" {
-			continue
-		}
 		mods = append(mods, mod)
 	}
 	return mods, nil
@@ -205,6 +203,20 @@ func ReadModules() ([]Module, error) {
 	return mods, nil
 }
 
+func FilterVendorModules(modules []Module) []Module {
+	var res []Module
+	for _, module := range modules {
+		// Don't vendor modules without paths / main modules.
+		if module.Dir == "" || module.Version == "" && module.Main {
+			continue
+		}
+
+		res = append(res, module)
+	}
+
+	return res
+}
+
 type Options struct {
 	SkipGoBin bool
 	SkipGoSrc bool
@@ -268,6 +280,8 @@ func LinkGoSrc(dstDir string) error {
 		return fmt.Errorf("error reading modules: %w", err)
 	}
 
+	mods = FilterVendorModules(mods)
+
 	nodes, err := BuildModuleNodes(mods)
 	if err != nil {
 		return fmt.Errorf("error building module tree: %w", err)

internal/internal_test.go

@@ -30,8 +30,8 @@ import (
 
 var _ = Describe("Internal", func() {
 	var (
-		tmpDir                                                   string
-		moduleA, moduleB, moduleB1, moduleB11, moduleB2, moduleC Module
+		tmpDir                                                            string
+		moduleA, moduleB, moduleB1, moduleB11, moduleB2, moduleC, moduleD Module
 	)
 	BeforeEach(func() {
 		var err error
@@ -41,6 +41,7 @@ var _ = Describe("Internal", func() {
 		moduleA = Module{
 			Path: "a",
 			Dir:  "/tmp/a",
+			Main: true,
 		}
 		moduleB = Module{
 			Path: "example.org/b",
@@ -62,6 +63,9 @@ var _ = Describe("Internal", func() {
 			Path: "example.org/user/c",
 			Dir:  "/tmp/example.org/user/c",
 		}
+		moduleD = Module{
+			Path: "example.org/d",
+		}
 	})
 	AfterEach(func() {
 		if tmpDir != "" {
@@ -146,7 +150,14 @@ var _ = Describe("Internal", func() {
 			mods, err := ParseModules(bytes.NewReader(data))
 			Expect(err).NotTo(HaveOccurred())
 
-			Expect(mods).To(Equal([]Module{moduleA, moduleB}))
+			Expect(mods).To(Equal([]Module{moduleA, moduleB, moduleD}))
+		})
+	})
+
+	Describe("FilterVendorModules", func() {
+		It("should correctly filter the modules", func() {
+			mods := FilterVendorModules([]Module{moduleA, moduleB, moduleD})
+			Expect(mods).To(Equal([]Module{moduleB}))
 		})
 	})
 

internal/testdata/modules.json.stream

@@ -1,6 +1,7 @@
 {
 	"Path": "a",
-	"Dir": "/tmp/a"
+	"Dir": "/tmp/a",
+	"Main": true
 }
 {
 	"Path": "example.org/b",