misc/cgo/testshared: fix tests in module mode

Updates #30228

Change-Id: I5cc739eb9fdfb648ec45e350d43d4cb02e450553
Reviewed-on: https://go-review.googlesource.com/c/163211
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

misc/cgo/testshared/overlaydir_test.go

+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package shared_test
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// overlayDir makes a minimal-overhead copy of srcRoot in which new files may be added.
+//
+// TODO: Once we no longer need to support the misc module in GOPATH mode,
+// factor this function out into a package to reduce duplication.
+func overlayDir(dstRoot, srcRoot string) error {
+	dstRoot = filepath.Clean(dstRoot)
+	if err := os.MkdirAll(dstRoot, 0777); err != nil {
+		return err
+	}
+
+	symBase, err := filepath.Rel(srcRoot, dstRoot)
+	if err != nil {
+		symBase, err = filepath.Abs(srcRoot)
+		if err != nil {
+			return err
+		}
+	}
+
+	return filepath.Walk(srcRoot, func(srcPath string, info os.FileInfo, err error) error {
+		if err != nil || srcPath == srcRoot {
+			return err
+		}
+
+		suffix := strings.TrimPrefix(srcPath, srcRoot)
+		for len(suffix) > 0 && suffix[0] == filepath.Separator {
+			suffix = suffix[1:]
+		}
+		dstPath := filepath.Join(dstRoot, suffix)
+
+		perm := info.Mode() & os.ModePerm
+		if info.Mode()&os.ModeSymlink != 0 {
+			info, err = os.Stat(srcPath)
+			if err != nil {
+				return err
+			}
+			perm = info.Mode() & os.ModePerm
+		}
+
+		// Always copy directories (don't symlink them).
+		// If we add a file in the overlay, we don't want to add it in the original.
+		if info.IsDir() {
+			return os.Mkdir(dstPath, perm)
+		}
+
+		// If the OS supports symlinks, use them instead of copying bytes.
+		if err := os.Symlink(filepath.Join(symBase, suffix), dstPath); err == nil {
+			return nil
+		}
+
+		// Otherwise, copy the bytes.
+		src, err := os.Open(srcPath)
+		if err != nil {
+			return err
+		}
+		defer src.Close()
+
+		dst, err := os.OpenFile(dstPath, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
+		if err != nil {
+			return err
+		}
+
+		_, err = io.Copy(dst, src)
+		if closeErr := dst.Close(); err == nil {
+			err = closeErr
+		}
+		return err
+	})
+}

misc/cgo/testshared/src/dep2/dep2.go → misc/cgo/testshared/testdata/dep2/dep2.go

 package dep2
 
-import "depBase"
+import "testshared/depBase"
 
 var W int = 1
 

misc/cgo/testshared/src/dep3/dep3.go → misc/cgo/testshared/testdata/dep3/dep3.go

@@ -7,8 +7,8 @@ package dep3
 // the type data in this case and later crash.
 
 import (
-	"dep2"
-	"depBase"
+	"testshared/dep2"
+	"testshared/depBase"
 )
 
 type Dep3 struct {

misc/cgo/testshared/src/exe/exe.go → misc/cgo/testshared/testdata/exe/exe.go

 package main
 
 import (
-	"depBase"
+	"testshared/depBase"
 	"os"
 	"reflect"
 	"runtime"

misc/cgo/testshared/src/exe2/exe2.go → misc/cgo/testshared/testdata/exe2/exe2.go

 package main
 
-import "dep2"
+import "testshared/dep2"
 
 func main() {
 	d := &dep2.Dep2{}

misc/cgo/testshared/src/exe3/exe3.go → misc/cgo/testshared/testdata/exe3/exe3.go

 package main
 
-import "dep3"
+import "testshared/dep3"
 
 func main() {
 	dep3.D3()

misc/cgo/testshared/src/explicit/explicit.go → misc/cgo/testshared/testdata/explicit/explicit.go

 package explicit
 
 import (
-	"implicit"
+	"testshared/implicit"
 )
 
 func E() int {

misc/cgo/testshared/src/global/main.go → misc/cgo/testshared/testdata/global/main.go

@@ -5,7 +5,7 @@
 package main
 
 import (
-	"globallib"
+	"testshared/globallib"
 )
 
 //go:noinline

misc/cgo/testshared/src/iface/main.go → misc/cgo/testshared/testdata/iface/main.go

@@ -4,8 +4,8 @@
 
 package main
 
-import "iface_a"
-import "iface_b"
+import "testshared/iface_a"
+import "testshared/iface_b"
 
 func main() {
 	if iface_a.F() != iface_b.F() {

misc/cgo/testshared/src/iface_a/a.go → misc/cgo/testshared/testdata/iface_a/a.go

@@ -4,7 +4,7 @@
 
 package iface_a
 
-import "iface_i"
+import "testshared/iface_i"
 
 //go:noinline
 func F() interface{} {

misc/cgo/testshared/src/iface_b/b.go → misc/cgo/testshared/testdata/iface_b/b.go

@@ -4,7 +4,7 @@
 
 package iface_b
 
-import "iface_i"
+import "testshared/iface_i"
 
 //go:noinline
 func F() interface{} {

misc/cgo/testshared/src/implicitcmd/implicitcmd.go → misc/cgo/testshared/testdata/implicitcmd/implicitcmd.go

 package main
 
 import (
-	"explicit"
-	"implicit"
+	"testshared/explicit"
+	"testshared/implicit"
 )
 
 func main() {