vfs: add flag --vfs-case-insensitive for windows/macOS mounts

rclone mount when run on Windows & macOS will now default to `--vfs-case-insensitive`.
This means that

vfs/vfs_case_test.go

@@ -0,0 +1,156 @@
+package vfs
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"github.com/rclone/rclone/fstest"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCaseSensitivity(t *testing.T) {
+	r := fstest.NewRun(t)
+	defer r.Finalise()
+
+	// Create test files
+	ctx := context.Background()
+	file1 := r.WriteObject(ctx, "FiLeA", "data1", t1)
+	file2 := r.WriteObject(ctx, "FiLeB", "data2", t2)
+	fstest.CheckItems(t, r.Fremote, file1, file2)
+
+	// Create file3 with name differing from file2 name only by case.
+	// On a case-Sensitive remote this will be a separate file.
+	// On a case-INsensitive remote this file will either not exist
+	// or overwrite file2 depending on how file system diverges.
+	file3 := r.WriteObject(ctx, "FilEb", "data3", t3)
+
+	// Create a case-Sensitive and case-INsensitive VFS
+	optCS := DefaultOpt
+	optCS.CaseInsensitive = false
+	vfsCS := New(r.Fremote, &optCS)
+
+	optCI := DefaultOpt
+	optCI.CaseInsensitive = true
+	vfsCI := New(r.Fremote, &optCI)
+
+	// Run basic checks that must pass on VFS of any type.
+	assertFileDataVFS(t, vfsCI, "FiLeA", "data1")
+	assertFileDataVFS(t, vfsCS, "FiLeA", "data1")
+
+	// Detect case sensitivity of the underlying remote.
+	remoteIsOK := true
+	if !checkFileDataVFS(t, vfsCS, "FiLeA", "data1") {
+		remoteIsOK = false
+	}
+	if !checkFileDataVFS(t, vfsCS, "FiLeB", "data2") {
+		remoteIsOK = false
+	}
+	if !checkFileDataVFS(t, vfsCS, "FilEb", "data3") {
+		remoteIsOK = false
+	}
+
+	// The remaining test is only meaningful on a case-Sensitive file system.
+	if !remoteIsOK {
+		t.Logf("SKIP: TestCaseSensitivity - remote is not fully case-sensitive")
+		return
+	}
+
+	// Continue with test as the underlying remote is fully case-Sensitive.
+	fstest.CheckItems(t, r.Fremote, file1, file2, file3)
+
+	// See how VFS handles case-INsensitive flag
+	assertFileDataVFS(t, vfsCI, "FiLeA", "data1")
+	assertFileDataVFS(t, vfsCI, "fileA", "data1")
+	assertFileDataVFS(t, vfsCI, "filea", "data1")
+	assertFileDataVFS(t, vfsCI, "FILEA", "data1")
+
+	assertFileDataVFS(t, vfsCI, "FiLeB", "data2")
+	assertFileDataVFS(t, vfsCI, "FilEb", "data3")
+
+	fd, err := vfsCI.OpenFile("fileb", os.O_RDONLY, 0777)
+	assert.Nil(t, fd)
+	assert.Error(t, err)
+	assert.NotEqual(t, err, ENOENT)
+
+	fd, err = vfsCI.OpenFile("FILEB", os.O_RDONLY, 0777)
+	assert.Nil(t, fd)
+	assert.Error(t, err)
+	assert.NotEqual(t, err, ENOENT)
+
+	// Run the same set of checks with case-Sensitive VFS, for comparison.
+	assertFileDataVFS(t, vfsCS, "FiLeA", "data1")
+
+	assertFileAbsentVFS(t, vfsCS, "fileA")
+	assertFileAbsentVFS(t, vfsCS, "filea")
+	assertFileAbsentVFS(t, vfsCS, "FILEA")
+
+	assertFileDataVFS(t, vfsCS, "FiLeB", "data2")
+	assertFileDataVFS(t, vfsCS, "FilEb", "data3")
+
+	assertFileAbsentVFS(t, vfsCS, "fileb")
+	assertFileAbsentVFS(t, vfsCS, "FILEB")
+}
+
+func checkFileDataVFS(t *testing.T, vfs *VFS, name string, expect string) bool {
+	fd, err := vfs.OpenFile(name, os.O_RDONLY, 0777)
+	if fd == nil || err != nil {
+		return false
+	}
+	defer func() {
+		// File must be closed - otherwise Run.cleanUp() will fail on Windows.
+		_ = fd.Close()
+	}()
+
+	fh, ok := fd.(*ReadFileHandle)
+	if !ok {
+		return false
+	}
+
+	size := len(expect)
+	buf := make([]byte, size)
+	num, err := fh.Read(buf)
+	if err != nil || num != size {
+		return false
+	}
+
+	return string(buf) == expect
+}
+
+func assertFileDataVFS(t *testing.T, vfs *VFS, name string, expect string) {
+	fd, errOpen := vfs.OpenFile(name, os.O_RDONLY, 0777)
+	assert.NotNil(t, fd)
+	assert.NoError(t, errOpen)
+
+	defer func() {
+		// File must be closed - otherwise Run.cleanUp() will fail on Windows.
+		if errOpen == nil && fd != nil {
+			_ = fd.Close()
+		}
+	}()
+
+	fh, ok := fd.(*ReadFileHandle)
+	require.True(t, ok)
+
+	size := len(expect)
+	buf := make([]byte, size)
+	numRead, errRead := fh.Read(buf)
+	assert.NoError(t, errRead)
+	assert.Equal(t, numRead, size)
+
+	assert.Equal(t, string(buf), expect)
+}
+
+func assertFileAbsentVFS(t *testing.T, vfs *VFS, name string) {
+	fd, err := vfs.OpenFile(name, os.O_RDONLY, 0777)
+	defer func() {
+		// File must be closed - otherwise Run.cleanUp() will fail on Windows.
+		if err == nil && fd != nil {
+			_ = fd.Close()
+		}
+	}()
+	assert.Nil(t, fd)
+	assert.Error(t, err)
+	assert.Equal(t, err, ENOENT)
+}