Migrate dagger.#Secret and dagger.#Stream to new format

- Refactored to keep every transformation of built-in types (e.g. FS,
  Secret, etc) to/from CUE in the same place (plancontext)
- dagger.#Service and dagger.#Secret are now following the new FS-like format
  (e.g. `_service: id: string`)
- Backward compatibility
- dagger.#Stream is now an alias for dagger.#Service

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

plancontext/context.go

@@ -2,18 +2,10 @@ package plancontext
 
 import (
 	"crypto/sha256"
-	"encoding/json"
 	"fmt"
 )
 
-type ContextKey string
-
 // Context holds the execution context for a plan.
-//
-// Usage:
-// ctx := plancontext.New()
-// id := ctx.Secrets.Register("mysecret")
-// secret := ctx.Secrets.Get(id)
 type Context struct {
 	Platform  *platformContext
 	FS        *fsContext
@@ -28,25 +20,26 @@ func New() *Context {
 			platform: defaultPlatform,
 		},
 		FS: &fsContext{
-			store: make(map[ContextKey]*FS),
+			store: make(map[string]*FS),
 		},
 		LocalDirs: &localDirContext{
-			store: make(map[ContextKey]*LocalDir),
+			store: []string{},
 		},
 		Secrets: &secretContext{
-			store: make(map[ContextKey]*Secret),
+			store: make(map[string]*Secret),
 		},
 		Services: &serviceContext{
-			store: make(map[ContextKey]*Service),
+			store: make(map[string]*Service),
 		},
 	}
 }
 
-func hashID(v interface{}) ContextKey {
-	data, err := json.Marshal(v)
-	if err != nil {
-		panic(err)
+func hashID(values ...string) string {
+	hash := sha256.New()
+	for _, v := range values {
+		if _, err := hash.Write([]byte(v)); err != nil {
+			panic(err)
+		}
 	}
-	hash := sha256.Sum256(data)
-	return ContextKey(fmt.Sprintf("%x", hash))
+	return fmt.Sprintf("%x", hash)
 }