Merge pull request #143 from AkihiroSuda/refactor-ref

cache, solver: refactor Reference interface

cache/refs.go

@@ -12,24 +12,25 @@ import (
 	"golang.org/x/net/context"
 )
 
-type ImmutableRef interface {
+// Ref is a reference to cacheable objects.
+type Ref interface {
 	Mountable
 	ID() string
 	Release(context.Context) error
 	Size(ctx context.Context) (int64, error)
+	Metadata() *metadata.StorageItem
+}
+
+type ImmutableRef interface {
+	Ref
 	Parent() ImmutableRef
 	Finalize(ctx context.Context) error // Make sure reference is flushed to driver
-	Metadata() *metadata.StorageItem
 	// Prepare() / ChainID() / Meta()
 }
 
 type MutableRef interface {
-	Mountable
-	ID() string
+	Ref
 	Commit(context.Context) (ImmutableRef, error)
-	Release(context.Context) error
-	Size(ctx context.Context) (int64, error)
-	Metadata() *metadata.StorageItem
 }
 
 type Mountable interface {

solver/solver.go

@@ -57,6 +57,8 @@ func NewLLBSolver(opt LLBOpt) *Solver {
 type ResolveOpFunc func(Vertex) (Op, error)
 
 // Reference is a reference to the object passed through the build steps.
+// This interface is a subset of the cache.Ref interface.
+// For ease of unit testing, this interface only has Release().
 type Reference interface {
 	Release(context.Context) error
 }