add a new method to indicate if the command provides files to snapshot

pkg/commands/add.go

@@ -116,6 +116,10 @@ func (a *AddCommand) FilesToSnapshot() []string {
 	return a.snapshotFiles
 }
 
+func (a *AddCommand) ProvidesFilesToSnapshot() bool {
+	return true
+}
+
 // String returns some information about the command for the image config
 func (a *AddCommand) String() string {
 	return a.cmd.String()

pkg/commands/base_command.go

@@ -32,6 +32,10 @@ func (b *BaseCommand) FilesToSnapshot() []string {
 	return []string{}
 }
 
+func (b *BaseCommand) ProvidesFilesToSnapshot() bool {
+	return false
+}
+
 func (b *BaseCommand) FilesUsedFromContext(_ *v1.Config, _ *dockerfile.BuildArgs) ([]string, error) {
 	return []string{}, nil
 }

pkg/commands/commands.go

@@ -37,6 +37,10 @@ type DockerCommand interface {
 	// A list of files to snapshot, empty for metadata commands or nil if we don't know
 	FilesToSnapshot() []string
 
+	// ProvidesFileToSnapshot is true for all metadata commands and commands which know
+	// list of files changed. False for Run command.
+	ProvidesFilesToSnapshot() bool
+
 	// Return a cache-aware implementation of this command, if it exists.
 	CacheCommand(v1.Image) DockerCommand
 

pkg/commands/copy.go

@@ -138,6 +138,10 @@ func (c *CopyCommand) MetadataOnly() bool {
 	return false
 }
 
+func (c *CopyCommand) ProvidesFilesToSnapshot() bool {
+	return true
+}
+
 func (c *CopyCommand) RequiresUnpackedFS() bool {
 	return true
 }
@@ -210,6 +214,14 @@ func (cr *CachingCopyCommand) FilesToSnapshot() []string {
 	return f
 }
 
+func (cr *CachingCopyCommand) MetadataOnly() bool {
+	return false
+}
+
+func (cr *CachingCopyCommand) ProvidesFilesToSnapshot() bool {
+	return true
+}
+
 func (cr *CachingCopyCommand) String() string {
 	if cr.cmd == nil {
 		return "nil command"

pkg/commands/run.go

@@ -151,6 +151,10 @@ func (r *RunCommand) FilesToSnapshot() []string {
 	return nil
 }
 
+func (r *RunCommand) ProvidesFilesToSnapshot() bool {
+	return false
+}
+
 // CacheCommand returns true since this command should be cached
 func (r *RunCommand) CacheCommand(img v1.Image) DockerCommand {
 
@@ -227,3 +231,11 @@ func (cr *CachingRunCommand) String() string {
 	}
 	return cr.cmd.String()
 }
+
+func (cr *CachingRunCommand) MetadataOnly() bool {
+	return false
+}
+
+func (cr *CachingRunCommand) RequiresUnpackedFS() bool {
+	return true
+}

pkg/commands/workdir.go

@@ -75,3 +75,7 @@ func (w *WorkdirCommand) String() string {
 func (w *WorkdirCommand) MetadataOnly() bool {
 	return false
 }
+
+func (w *WorkdirCommand) ProvidesFilesToSnapshot() bool {
+	return true
+}