Restore support for testing js package.

The _test.go file needs to be accessed via the build context's file
system interface.

Take into account the fact that the js and nosync packages are now
effectively virtual, and don't have a corresponding physical directory.
Use current directory when running tests with Node.js, otherwise it
would fail with "directory not exist" error.

build/build.go

@@ -130,6 +130,7 @@ func Import(path string, mode build.ImportMode, installSuffix string, buildTags
 
 func importWithSrcDir(bctx build.Context, path string, srcDir string, mode build.ImportMode, installSuffix string) (*PackageData, error) {
 	// bctx is passed by value, so it can be modified here.
+	var isVirtual bool
 	switch path {
 	case "syscall":
 		// syscall needs to use a typical GOARCH like amd64 to pick up definitions for _Socklen, BpfInsn, IFNAMSIZ, Timeval, BpfStat, SYS_FCNTL, Flock_t, etc.
@@ -148,6 +149,7 @@ func importWithSrcDir(bctx build.Context, path string, srcDir string, mode build
 		// These packages are already embedded via gopherjspkg.FS virtual filesystem (which can be
 		// safely vendored). Don't try to use vendor directory to resolve them.
 		mode |= build.IgnoreVendor
+		isVirtual = true
 	}
 	pkg, err := bctx.Import(path, srcDir, mode)
 	if err != nil {
@@ -192,7 +194,7 @@ func importWithSrcDir(bctx build.Context, path string, srcDir string, mode build
 		return nil, err
 	}
 
-	return &PackageData{Package: pkg, JSFiles: jsFiles}, nil
+	return &PackageData{Package: pkg, JSFiles: jsFiles, IsVirtual: isVirtual}, nil
 }
 
 // excludeExecutable excludes all executable implementation .go files.
@@ -459,6 +461,7 @@ type PackageData struct {
 	IsTest     bool // IsTest is true if the package is being built for running tests.
 	SrcModTime time.Time
 	UpToDate   bool
+	IsVirtual  bool // If true, the package does not have a corresponding physical directory on disk.
 }
 
 type Session struct {
@@ -500,6 +503,9 @@ func NewSession(options *Options) *Session {
 	return s
 }
 
+// BuildContext returns the session's build context.
+func (s *Session) BuildContext() *build.Context { return s.bctx }
+
 func (s *Session) InstallSuffix() string {
 	if s.options.Minify {
 		return "min"

tool.go

@@ -37,6 +37,7 @@ import (
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 	"golang.org/x/crypto/ssh/terminal"
+	"golang.org/x/tools/go/buildutil"
 )
 
 var currentDirectory string
@@ -331,17 +332,17 @@ func main() {
 				}
 				s := gbuild.NewSession(options)
 
-				tests := &testFuncs{Package: pkg.Package}
+				tests := &testFuncs{BuildContext: s.BuildContext(), Package: pkg.Package}
 				collectTests := func(testPkg *gbuild.PackageData, testPkgName string, needVar *bool) error {
 					if testPkgName == "_test" {
 						for _, file := range pkg.TestGoFiles {
-							if err := tests.load(filepath.Join(pkg.Package.Dir, file), testPkgName, &tests.ImportTest, &tests.NeedTest); err != nil {
+							if err := tests.load(pkg.Package.Dir, file, testPkgName, &tests.ImportTest, &tests.NeedTest); err != nil {
 								return err
 							}
 						}
 					} else {
 						for _, file := range pkg.XTestGoFiles {
-							if err := tests.load(filepath.Join(pkg.Package.Dir, file), "_xtest", &tests.ImportXtest, &tests.NeedXtest); err != nil {
+							if err := tests.load(pkg.Package.Dir, file, "_xtest", &tests.ImportXtest, &tests.NeedXtest); err != nil {
 								return err
 							}
 						}
@@ -453,7 +454,7 @@ func main() {
 				}
 				status := "ok  "
 				start := time.Now()
-				if err := runNode(outfile.Name(), args, pkg.Dir, options.Quiet); err != nil {
+				if err := runNode(outfile.Name(), args, runTestDir(pkg), options.Quiet); err != nil {
 					if _, ok := err.(*exec.ExitError); !ok {
 						return err
 					}
@@ -740,6 +741,8 @@ func sprintError(err error) string {
 	}
 }
 
+// runNode runs script with args using Node.js in directory dir.
+// If dir is empty string, current directory is used.
 func runNode(script string, args []string, dir string, quiet bool) error {
 	var allArgs []string
 	if b, _ := strconv.ParseBool(os.Getenv("SOURCE_MAP_SUPPORT")); os.Getenv("SOURCE_MAP_SUPPORT") == "" || b {
@@ -790,16 +793,28 @@ func runNode(script string, args []string, dir string, quiet bool) error {
 	return err
 }
 
+// runTestDir returns the directory for Node.js to use when running tests for package p.
+// Empty string means current directory.
+func runTestDir(p *gbuild.PackageData) string {
+	if p.IsVirtual {
+		// The package is virtual and doesn't have a physical directory. Use current directory.
+		return ""
+	}
+	// Run tests in the package directory.
+	return p.Dir
+}
+
 type testFuncs struct {
-	Tests       []testFunc
-	Benchmarks  []testFunc
-	Examples    []testFunc
-	TestMain    *testFunc
-	Package     *build.Package
-	ImportTest  bool
-	NeedTest    bool
-	ImportXtest bool
-	NeedXtest   bool
+	BuildContext *build.Context
+	Tests        []testFunc
+	Benchmarks   []testFunc
+	Examples     []testFunc
+	TestMain     *testFunc
+	Package      *build.Package
+	ImportTest   bool
+	NeedTest     bool
+	ImportXtest  bool
+	NeedXtest    bool
 }
 
 type testFunc struct {
@@ -811,8 +826,8 @@ type testFunc struct {
 
 var testFileSet = token.NewFileSet()
 
-func (t *testFuncs) load(filename, pkg string, doImport, seen *bool) error {
-	f, err := parser.ParseFile(testFileSet, filename, nil, parser.ParseComments)
+func (t *testFuncs) load(dir, file, pkg string, doImport, seen *bool) error {
+	f, err := buildutil.ParseFile(testFileSet, t.BuildContext, nil, dir, file, parser.ParseComments)
 	if err != nil {
 		return err
 	}