engine: Task PreRun Hook

Tasks now have a PreRun hook that gets called before buildkit kicks in.
Allows to support local access without special casing.

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

plan/task/inputdirectory.go

@@ -2,6 +2,9 @@ package task
 
 import (
 	"context"
+	"errors"
+	"fmt"
+	"os"
 
 	"github.com/moby/buildkit/client/llb"
 	"github.com/rs/zerolog/log"
@@ -17,6 +20,20 @@ func init() {
 type inputDirectoryTask struct {
 }
 
+func (c *inputDirectoryTask) PreRun(ctx context.Context, pctx *plancontext.Context, v *compiler.Value) error {
+	path, err := v.Lookup("path").AbsPath()
+	if err != nil {
+		return err
+	}
+
+	if _, err := os.Stat(path); errors.Is(err, os.ErrNotExist) {
+		return fmt.Errorf("path %q does not exist", path)
+	}
+	pctx.LocalDirs.Add(path)
+
+	return nil
+}
+
 func (c *inputDirectoryTask) Run(ctx context.Context, pctx *plancontext.Context, s solver.Solver, v *compiler.Value) (*compiler.Value, error) {
 	path, err := v.Lookup("path").AbsPath()
 	if err != nil {

plan/task/task.go

@@ -29,6 +29,12 @@ type Task interface {
 	Run(ctx context.Context, pctx *plancontext.Context, s solver.Solver, v *compiler.Value) (*compiler.Value, error)
 }
 
+type PreRunner interface {
+	Task
+
+	PreRun(ctx context.Context, pctx *plancontext.Context, v *compiler.Value) error
+}
+
 // Register a task type and initializer
 func Register(typ string, f NewFunc) {
 	tasks.Store(typ, f)