check cfg filename case on case insensitive systems

- `fs`
  - Export `IsCaseSensitiveFilesystem`. Add and run test on windows, linux.
  - Add function `ReadActualFilenames` to read actual file names of given
    string slice. Add tests to be run on windows.
- `project`
  - Add function `checkCfgFilenames` to check the filenames for manifest
    and lock have the expected case. Use `fs#IsCaseSensitiveFilesystem`
    for an early return as the check is costly. Add test to be run on windows.
- `context`
  - Call `project.go#checkCfgFilenames` after resolving project root. Add test
    for invalid manifest file name to be run on windows.

context.go

@@ -103,6 +103,11 @@ func (c *Ctx) LoadProject() (*Project, error) {
 		return nil, err
 	}
 
+	err = checkCfgFilenames(root)
+	if err != nil {
+		return nil, err
+	}
+
 	p := new(Project)
 
 	if err = p.SetRoot(root); err != nil {

context_test.go

@@ -5,6 +5,7 @@
 package dep
 
 import (
+	"fmt"
 	"io/ioutil"
 	"log"
 	"os"
@@ -263,6 +264,50 @@ func TestLoadProjectNoSrcDir(t *testing.T) {
 	}
 }
 
+func TestLoadProjectCfgFileCase(t *testing.T) {
+	if runtime.GOOS != "windows" && runtime.GOOS == "darwin" {
+		t.Skip("skip this test on non-Windows, non-macOS")
+	}
+
+	// Here we test that a manifest filename with incorrect case
+	// throws an error. Similar error will also be thrown for the
+	// lock file as well which has been tested in
+	// `project_test.go#TestCheckCfgFilenames`. So not repeating here.
+
+	h := test.NewHelper(t)
+	defer h.Cleanup()
+
+	invalidMfName := strings.ToLower(ManifestName)
+
+	wd := filepath.Join("src", "test")
+	h.TempFile(filepath.Join(wd, invalidMfName), "")
+
+	ctx := &Ctx{
+		Out: discardLogger,
+		Err: discardLogger,
+	}
+
+	err := ctx.SetPaths(h.Path(wd), h.Path("."))
+	if err != nil {
+		t.Fatalf("%+v", err)
+	}
+
+	_, err = ctx.LoadProject()
+
+	if err == nil {
+		t.Fatal("should have returned 'Manifest Filename' error")
+	}
+
+	expectedErrMsg := fmt.Sprintf(
+		"manifest filename '%s' does not match '%s'",
+		invalidMfName, ManifestName,
+	)
+
+	if err.Error() != expectedErrMsg {
+		t.Fatalf("unexpected error: %+v", err)
+	}
+}
+
 // TestCaseInsentitive is test for Windows. This should work even though set
 // difference letter cases in GOPATH.
 func TestCaseInsentitiveGOPATH(t *testing.T) {

internal/fs/fs.go

@@ -35,9 +35,9 @@ func HasFilepathPrefix(path, prefix string) (bool, error) {
 	// handling of volume name/drive letter on Windows. vnPath and vnPrefix
 	// are first compared, and then used to initialize initial values of p and
 	// d which will be appended to for incremental checks using
-	// isCaseSensitiveFilesystem and then equality.
+	// IsCaseSensitiveFilesystem and then equality.
 
-	// no need to check isCaseSensitiveFilesystem because VolumeName return
+	// no need to check IsCaseSensitiveFilesystem because VolumeName return
 	// empty string on all non-Windows machines
 	vnPath := strings.ToLower(filepath.VolumeName(path))
 	vnPrefix := strings.ToLower(filepath.VolumeName(prefix))
@@ -82,7 +82,7 @@ func HasFilepathPrefix(path, prefix string) (bool, error) {
 		// something like ext4 filesystem mounted on FAT
 		// mountpoint, mounted on ext4 filesystem, i.e. the
 		// problematic filesystem is not the last one.
-		caseSensitive, err := isCaseSensitiveFilesystem(filepath.Join(d, dirs[i]))
+		caseSensitive, err := IsCaseSensitiveFilesystem(filepath.Join(d, dirs[i]))
 		if err != nil {
 			return false, errors.Wrap(err, "failed to check filepath prefix")
 		}
@@ -135,7 +135,7 @@ func EquivalentPaths(p1, p2 string) (bool, error) {
 	}
 
 	if p1Filename != "" || p2Filename != "" {
-		caseSensitive, err := isCaseSensitiveFilesystem(filepath.Join(p1, p1Filename))
+		caseSensitive, err := IsCaseSensitiveFilesystem(filepath.Join(p1, p1Filename))
 		if err != nil {
 			return false, errors.Wrap(err, "could not check for filesystem case-sensitivity")
 		}
@@ -193,7 +193,7 @@ func renameByCopy(src, dst string) error {
 	return errors.Wrapf(os.RemoveAll(src), "cannot delete %s", src)
 }
 
-// isCaseSensitiveFilesystem determines if the filesystem where dir
+// IsCaseSensitiveFilesystem determines if the filesystem where dir
 // exists is case sensitive or not.
 //
 // CAVEAT: this function works by taking the last component of the given
@@ -212,7 +212,7 @@ func renameByCopy(src, dst string) error {
 // If the input directory is such that the last component is composed
 // exclusively of case-less codepoints (e.g.  numbers), this function will
 // return false.
-func isCaseSensitiveFilesystem(dir string) (bool, error) {
+func IsCaseSensitiveFilesystem(dir string) (bool, error) {
 	alt := filepath.Join(filepath.Dir(dir), genTestFilename(filepath.Base(dir)))
 
 	dInfo, err := os.Stat(dir)
@@ -264,6 +264,89 @@ func genTestFilename(str string) string {
 	}, str)
 }
 
+var errPathNotDir = errors.New("given path is not a directory")
+
+// ReadActualFilenames is used to determine the actual file names in given directory.
+//
+// On case sensitive file systems like ext4, it will check if those files exist using
+// `os.Stat` and return a map with key and value as filenames which exist in the folder.
+//
+// Otherwise, it reads the contents of the directory
+func ReadActualFilenames(dirPath string, names []string) (map[string]string, error) {
+	actualFilenames := make(map[string]string, len(names))
+	if len(names) <= 0 {
+		// This isn't expected to happen for current usage.
+		// Adding edge case handling, maybe useful in future
+		return actualFilenames, nil
+	}
+	// First, check that the given path is valid and it is a directory
+	dirStat, err := os.Stat(dirPath)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to read actual filenames")
+	}
+
+	if !dirStat.IsDir() {
+		return nil, errPathNotDir
+	}
+
+	// Ideally, we would use `os.Stat` for getting the actual file names
+	// but that returns the name we passed in as an argument and not the actual filename.
+	// So we are forced to list the directory contents and check
+	// against that. Since this check is costly, we do it only if absolutely necessary.
+	caseSensitive, err := IsCaseSensitiveFilesystem(dirPath)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to read actual filenames")
+	}
+	if caseSensitive {
+		// There will be no difference between actual filename and given filename
+		// So just check if those files exist.
+		for _, name := range names {
+			_, err := os.Stat(filepath.Join(dirPath, name))
+			if err == nil {
+				actualFilenames[name] = name
+			} else if !os.IsNotExist(err) {
+				// Some unexpected err, return it.
+				return nil, errors.Wrap(err, "failed to read actual filenames")
+			}
+		}
+		return actualFilenames, nil
+	}
+
+	dir, err := os.Open(dirPath)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to read actual filenames")
+	}
+	defer dir.Close()
+
+	// Pass -1 to read all files in directory
+	files, err := dir.Readdir(-1)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to read actual filenames")
+	}
+
+	// namesMap holds the mapping from lowercase name to search name.
+	// Using this, we can avoid repeatedly looping through names.
+	namesMap := make(map[string]string, len(names))
+	for _, name := range names {
+		namesMap[strings.ToLower(name)] = name
+	}
+
+	for _, file := range files {
+		if file.Mode().IsRegular() {
+			searchName, ok := namesMap[strings.ToLower(file.Name())]
+			if ok {
+				// We are interested in this file, case insensitive match successful
+				actualFilenames[searchName] = file.Name()
+				if len(actualFilenames) == len(names) {
+					// We found all that we were looking for
+					return actualFilenames, nil
+				}
+			}
+		}
+	}
+	return actualFilenames, nil
+}
+
 var (
 	errSrcNotDir = errors.New("source is not a directory")
 	errDstExist  = errors.New("destination already exists")

internal/fs/fs_test.go

@@ -8,6 +8,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"strings"
 	"testing"
@@ -169,7 +170,7 @@ func TestEquivalentPaths(t *testing.T) {
 		{strings.ToLower(h.Path("dir")), strings.ToUpper(h.Path("dir")), false, true, true},
 	}
 
-	caseSensitive, err := isCaseSensitiveFilesystem(h.Path("dir"))
+	caseSensitive, err := IsCaseSensitiveFilesystem(h.Path("dir"))
 	if err != nil {
 		t.Fatal("unexpcted error:", err)
 	}
@@ -229,6 +230,99 @@ func TestRenameWithFallback(t *testing.T) {
 	}
 }
 
+func TestIsCaseSensitiveFilesystem(t *testing.T) {
+	isLinux := runtime.GOOS == "linux"
+	isWindows := runtime.GOOS == "windows"
+	isMacOS := runtime.GOOS == "darwin"
+
+	if !isLinux && !isWindows && !isMacOS {
+		t.Skip("Run this test on Windows, Linux and macOS only")
+	}
+
+	dir, err := ioutil.TempDir("", "TestCaseSensitivity")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	var want bool
+	if isLinux {
+		want = true
+	} else {
+		want = false
+	}
+
+	got, err := IsCaseSensitiveFilesystem(dir)
+
+	if err != nil {
+		t.Fatalf("unexpected error message: \n\t(GOT) %+v", err)
+	}
+
+	if want != got {
+		t.Fatalf("unexpected value returned: \n\t(GOT) %t\n\t(WNT) %t", got, want)
+	}
+}
+
+func TestReadActualFilenames(t *testing.T) {
+	if runtime.GOOS != "windows" && runtime.GOOS == "darwin" {
+		t.Skip("skip this test on non-Windows, non-macOS")
+	}
+
+	h := test.NewHelper(t)
+	defer h.Cleanup()
+
+	h.TempDir("")
+	tmpPath := h.Path(".")
+
+	_, err := ReadActualFilenames(filepath.Join(tmpPath, "does_not_exists"), []string{""})
+	switch {
+	case err == nil:
+		t.Fatal("expected err for non-existing folder")
+	case !os.IsNotExist(err):
+		t.Fatalf("unexpected error: %+v", err)
+	}
+	h.TempFile("tmpFile", "")
+	_, err = ReadActualFilenames(h.Path("tmpFile"), []string{""})
+	switch {
+	case err == nil:
+		t.Fatal("expected err for passing file instead of directory")
+	case err != errPathNotDir:
+		t.Fatalf("unexpected error: %+v", err)
+	}
+
+	cases := []struct {
+		createFiles []string
+		names       []string
+		want        map[string]string
+	}{
+		{nil, nil, map[string]string{}}, {
+			[]string{"test1.txt"},
+			[]string{"Test1.txt"},
+			map[string]string{"Test1.txt": "test1.txt"},
+		}, {
+			[]string{"test2.txt", "test3.TXT"},
+			[]string{"test2.txt", "Test3.txt", "Test4.txt"},
+			map[string]string{
+				"test2.txt": "test2.txt",
+				"Test3.txt": "test3.TXT",
+				"Test4.txt": "",
+			},
+		},
+	}
+	for _, c := range cases {
+		for _, file := range c.createFiles {
+			h.TempFile(file, "")
+		}
+		got, err := ReadActualFilenames(tmpPath, c.names)
+		if err != nil {
+			t.Fatalf("unexpected error: %+v", err)
+		}
+		if !reflect.DeepEqual(c.want, got) {
+			t.Fatalf("returned value does not match expected: \n\t(GOT) %v\n\t(WNT) %v", got, c.want)
+		}
+	}
+}
+
 func TestGenTestFilename(t *testing.T) {
 	cases := []struct {
 		str  string
@@ -254,11 +348,11 @@ func TestGenTestFilename(t *testing.T) {
 
 func BenchmarkGenTestFilename(b *testing.B) {
 	cases := []string{
-		"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
-		"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
-		"αααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααααα",
-		"11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111",
-		"⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘⌘",
+		strings.Repeat("a", 128),
+		strings.Repeat("A", 128),
+		strings.Repeat("α", 128),
+		strings.Repeat("1", 128),
+		strings.Repeat("⌘", 128),
 	}
 
 	for i := 0; i < b.N; i++ {
@@ -613,6 +707,7 @@ func TestCopyFileLongFilePath(t *testing.T) {
 
 	h := test.NewHelper(t)
 	h.TempDir(".")
+	defer h.Cleanup()
 
 	tmpPath := h.Path(".")