Skip sync warning if no sync paths are defined (#1926)

## Changes

Users can configure the bundle to not synchronize any files with:
```yaml
sync:
  paths: []
```

If it is explicitly configured as an empty list, the validate command
must not warn about not having any files to synchronize. The warning
exists to alert users who are unintentionally not synchronizing any
files (they might have a `.gitignore` pattern that matches everything).

Closes #1663.

## Tests

* New unit test.

bundle/config/validate/files_to_sync.go

@@ -21,6 +21,12 @@ func (v *filesToSync) Name() string {
 }
 
 func (v *filesToSync) Apply(ctx context.Context, rb bundle.ReadOnlyBundle) diag.Diagnostics {
+	// The user may be intentional about not synchronizing any files.
+	// In this case, we should not show any warnings.
+	if len(rb.Config().Sync.Paths) == 0 {
+		return nil
+	}
+
 	sync, err := files.GetSync(ctx, rb)
 	if err != nil {
 		return diag.FromErr(err)
@@ -31,6 +37,7 @@ func (v *filesToSync) Apply(ctx context.Context, rb bundle.ReadOnlyBundle) diag.
 		return diag.FromErr(err)
 	}
 
+	// If there are files to sync, we don't need to show any warnings.
 	if len(fl) != 0 {
 		return nil
 	}

bundle/config/validate/files_to_sync_test.go

@@ -0,0 +1,105 @@
+package validate
+
+import (
+	"context"
+	"testing"
+
+	"github.com/databricks/cli/bundle"
+	"github.com/databricks/cli/bundle/config"
+	"github.com/databricks/cli/internal/testutil"
+	"github.com/databricks/cli/libs/diag"
+	"github.com/databricks/cli/libs/vfs"
+	sdkconfig "github.com/databricks/databricks-sdk-go/config"
+	"github.com/databricks/databricks-sdk-go/experimental/mocks"
+	"github.com/databricks/databricks-sdk-go/service/iam"
+	"github.com/databricks/databricks-sdk-go/service/workspace"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFilesToSync_NoPaths(t *testing.T) {
+	b := &bundle.Bundle{
+		Config: config.Root{
+			Sync: config.Sync{
+				Paths: []string{},
+			},
+		},
+	}
+
+	ctx := context.Background()
+	rb := bundle.ReadOnly(b)
+	diags := bundle.ApplyReadOnly(ctx, rb, FilesToSync())
+	assert.Empty(t, diags)
+}
+
+func setupBundleForFilesToSyncTest(t *testing.T) *bundle.Bundle {
+	dir := t.TempDir()
+
+	testutil.Touch(t, dir, "file1")
+	testutil.Touch(t, dir, "file2")
+
+	b := &bundle.Bundle{
+		BundleRootPath: dir,
+		BundleRoot:     vfs.MustNew(dir),
+		SyncRootPath:   dir,
+		SyncRoot:       vfs.MustNew(dir),
+		Config: config.Root{
+			Bundle: config.Bundle{
+				Target: "default",
+			},
+			Workspace: config.Workspace{
+				FilePath: "/this/doesnt/matter",
+				CurrentUser: &config.User{
+					User: &iam.User{},
+				},
+			},
+			Sync: config.Sync{
+				// Paths are relative to [SyncRootPath].
+				Paths: []string{"."},
+			},
+		},
+	}
+
+	m := mocks.NewMockWorkspaceClient(t)
+	m.WorkspaceClient.Config = &sdkconfig.Config{
+		Host: "https://foo.com",
+	}
+
+	// The initialization logic in [sync.New] performs a check on the destination path.
+	// Removing this check at initialization time is tbd...
+	m.GetMockWorkspaceAPI().EXPECT().GetStatusByPath(mock.Anything, "/this/doesnt/matter").Return(&workspace.ObjectInfo{
+		ObjectType: workspace.ObjectTypeDirectory,
+	}, nil)
+
+	b.SetWorkpaceClient(m.WorkspaceClient)
+	return b
+}
+
+func TestFilesToSync_EverythingIgnored(t *testing.T) {
+	b := setupBundleForFilesToSyncTest(t)
+
+	// Ignore all files.
+	testutil.WriteFile(t, "*\n.*\n", b.BundleRootPath, ".gitignore")
+
+	ctx := context.Background()
+	rb := bundle.ReadOnly(b)
+	diags := bundle.ApplyReadOnly(ctx, rb, FilesToSync())
+	require.Equal(t, 1, len(diags))
+	assert.Equal(t, diag.Warning, diags[0].Severity)
+	assert.Equal(t, "There are no files to sync, please check your .gitignore", diags[0].Summary)
+}
+
+func TestFilesToSync_EverythingExcluded(t *testing.T) {
+	b := setupBundleForFilesToSyncTest(t)
+
+	// Exclude all files.
+	b.Config.Sync.Exclude = []string{"*"}
+
+	ctx := context.Background()
+	rb := bundle.ReadOnly(b)
+	diags := bundle.ApplyReadOnly(ctx, rb, FilesToSync())
+	require.Equal(t, 1, len(diags))
+	assert.Equal(t, diag.Warning, diags[0].Severity)
+	assert.Equal(t, "There are no files to sync, please check your .gitignore and sync.exclude configuration", diags[0].Summary)
+}