Ensure we can Marshall #Scratch as CUE

Signed-off-by: Joel Longtine <joel@dagger.io>

plan/task/build.go

@@ -115,15 +115,20 @@ func (t *buildTask) dockerfile(ctx context.Context, pctx *plancontext.Context, s
 		return nil, err
 	}
 
+	var solvedRef bkgw.Reference
+	if ref != nil {
 		st, err := ref.ToState()
 		if err != nil {
 			return nil, err
 		}
 
-	solvedRef, err := s.Solve(ctx, st, pctx.Platform.Get())
+		solvedRef, err = s.Solve(ctx, st, pctx.Platform.Get())
 		if err != nil {
 			return nil, err
 		}
+	} else {
+		solvedRef = ref
+	}
 
 	// Image metadata
 	meta, ok := res.Metadata[exptypes.ExporterImageConfigKey]

plancontext/fs.go

@@ -42,9 +42,15 @@ func (fs *FS) State() (llb.State, error) {
 
 func (fs *FS) MarshalCUE() *compiler.Value {
 	v := compiler.NewValue()
+	if fs.result == nil {
+		if err := v.FillPath(fsIDPath, nil); err != nil {
+			panic(err)
+		}
+	} else {
 		if err := v.FillPath(fsIDPath, fs.id); err != nil {
 			panic(err)
 		}
+	}
 	return v
 }
 

tests/tasks.bats

@@ -92,6 +92,8 @@ setup() {
 @test "task: #Scratch" {
     cd "$TESTDIR"/tasks/scratch
     "$DAGGER" --europa up ./scratch.cue -l debug
+    "$DAGGER" --europa up ./scratch_build_scratch.cue -l debug
+    "$DAGGER" --europa up ./scratch_writefile.cue -l debug
 }
 
 @test "task: #Subdir" {

tests/tasks/scratch/scratch_build_scratch.cue

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"alpha.dagger.io/europa/dagger/engine"
+)
+
+engine.#Plan & {
+	actions: {
+		write: engine.#WriteFile & {
+			input:       engine.#Scratch
+			path:        "/.dockerignore"
+			contents:    "Dockerfile"
+			permissions: 700
+		}
+
+		build: engine.#Build & {
+			source: write.output
+			dockerfile: contents: """
+				FROM scratch
+				"""
+			// Assert that output is engine.#Scratch
+			output: engine.#Scratch
+		}
+	}
+}

tests/tasks/scratch/scratch_writefile.cue

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"alpha.dagger.io/europa/dagger/engine"
+)
+
+engine.#Plan & {
+	actions: {
+		write: engine.#WriteFile & {
+			input:       engine.#Scratch
+			path:        "/testing"
+			contents:    "1,2,3"
+			permissions: 700
+		}
+		readfile: engine.#ReadFile & {
+			input: write.output
+			path:  "/testing"
+		} & {
+			// assert result
+			contents: "1,2,3"
+		}
+	}
+}