{do:"subdir"} to select a subdirectory in a script

Signed-off-by: Solomon Hykes <sh.github.6811@hykes.org>

dagger/gen.go

@@ -60,7 +60,7 @@ package dagger
 #Script: [...#Op]
 
 // One operation in a script
-#Op: #FetchContainer | #FetchGit | #Export | #Exec | #Local | #Copy | #Load
+#Op: #FetchContainer | #FetchGit | #Export | #Exec | #Local | #Copy | #Load | #Subdir
 
 // Export a value from fs state to cue
 #Export: {
@@ -83,6 +83,11 @@ package dagger
 	from: #Component | #Script
 }
 
+#Subdir: {
+	do:  "subdir"
+	dir: string | *"/"
+}
+
 #Exec: {
 	do: "exec"
 	args: [...string]

dagger/op.go

@@ -94,6 +94,7 @@ func (op *Op) Action() (Action, error) {
 		"#FetchGit":       op.FetchGit,
 		"#Local":          op.Local,
 		"#Load":           op.Load,
+		"#Subdir":         op.Subdir,
 	}
 	for def, action := range actions {
 		if err := op.Validate(def); err == nil {
@@ -108,6 +109,26 @@ func (op *Op) Validate(defs ...string) error {
 	return op.v.Validate(defs...)
 }
 
+func (op *Op) Subdir(ctx context.Context, fs FS, out *Fillable) (FS, error) {
+	// FIXME: this could be more optimized by carrying subdir path as metadata,
+	//  and using it in copy, load or mount.
+
+	dir, err := op.Get("dir").String()
+	if err != nil {
+		return fs, err
+	}
+	return fs.Change(func(st llb.State) llb.State {
+		return st.File(llb.Copy(
+			fs.LLB(),
+			dir,
+			"/",
+			&llb.CopyInfo{
+				CopyDirContentsOnly: true,
+			},
+		))
+	}), nil
+}
+
 func (op *Op) Copy(ctx context.Context, fs FS, out *Fillable) (FS, error) {
 	// Decode copy options
 	src, err := op.Get("src").String()

dagger/spec.cue

@@ -55,7 +55,7 @@ package dagger
 #Script: [...#Op]
 
 // One operation in a script
-#Op: #FetchContainer | #FetchGit | #Export | #Exec | #Local | #Copy | #Load
+#Op: #FetchContainer | #FetchGit | #Export | #Exec | #Local | #Copy | #Load | #Subdir
 
 // Export a value from fs state to cue
 #Export: {
@@ -78,6 +78,11 @@ package dagger
 	from: #Component | #Script
 }
 
+#Subdir: {
+	do:  "subdir"
+	dir: string | *"/"
+}
+
 #Exec: {
 	do: "exec"
 	args: [...string]