Add support for Merge and Diff fs operations.

Signed-off-by: Erik Sipsma <erik@sipsma.dev>

plan/task/diff.go

@@ -0,0 +1,48 @@
+package task
+
+import (
+	"context"
+
+	"github.com/moby/buildkit/client/llb"
+	"go.dagger.io/dagger/compiler"
+	"go.dagger.io/dagger/plancontext"
+	"go.dagger.io/dagger/solver"
+)
+
+func init() {
+	Register("Diff", func() Task { return &diffTask{} })
+}
+
+type diffTask struct {
+}
+
+func (t diffTask) Run(ctx context.Context, pctx *plancontext.Context, s solver.Solver, v *compiler.Value) (*compiler.Value, error) {
+	lowerFS, err := pctx.FS.FromValue(v.Lookup("lower"))
+	if err != nil {
+		return nil, err
+	}
+	lower, err := lowerFS.State()
+	if err != nil {
+		return nil, err
+	}
+
+	upperFS, err := pctx.FS.FromValue(v.Lookup("upper"))
+	if err != nil {
+		return nil, err
+	}
+	upper, err := upperFS.State()
+	if err != nil {
+		return nil, err
+	}
+
+	st := llb.Diff(lower, upper)
+	result, err := s.Solve(ctx, st, pctx.Platform.Get())
+	if err != nil {
+		return nil, err
+	}
+
+	fs := pctx.FS.New(result)
+	return compiler.NewValue().FillFields(map[string]interface{}{
+		"output": fs.MarshalCUE(),
+	})
+}

plan/task/merge.go

@@ -0,0 +1,48 @@
+package task
+
+import (
+	"context"
+
+	"github.com/moby/buildkit/client/llb"
+	"go.dagger.io/dagger/compiler"
+	"go.dagger.io/dagger/plancontext"
+	"go.dagger.io/dagger/solver"
+)
+
+func init() {
+	Register("Merge", func() Task { return &mergeTask{} })
+}
+
+type mergeTask struct {
+}
+
+func (t mergeTask) Run(ctx context.Context, pctx *plancontext.Context, s solver.Solver, v *compiler.Value) (*compiler.Value, error) {
+	inputs, err := v.Lookup("inputs").List()
+	if err != nil {
+		return nil, err
+	}
+
+	inputStates := make([]llb.State, len(inputs))
+	for i, input := range inputs {
+		inputFS, err := pctx.FS.FromValue(input)
+		if err != nil {
+			return nil, err
+		}
+		inputState, err := inputFS.State()
+		if err != nil {
+			return nil, err
+		}
+		inputStates[i] = inputState
+	}
+
+	st := llb.Merge(inputStates)
+	result, err := s.Solve(ctx, st, pctx.Platform.Get())
+	if err != nil {
+		return nil, err
+	}
+
+	fs := pctx.FS.New(result)
+	return compiler.NewValue().FillFields(map[string]interface{}{
+		"output": fs.MarshalCUE(),
+	})
+}