Don't cache projects when loaded

Because the project ID doesn't indicate its contents, it should not be cached when it's loaded. Additionally the id should not be calculated from its contents.

src/AssetType.js

@@ -8,32 +8,38 @@ const DataFormat = require('./DataFormat');
  * @property {string} name - The human-readable name of this asset type.
  * @property {DataFormat} runtimeFormat - The format used for runtime, in-memory storage of this asset. For example, a
  *     project stored in SB2 format on disk will be returned as JSON when loaded into memory.
+ * @property {boolean} immutable - Indicates if the asset id is determined by the asset content.
  */
 const AssetType = {
     ImageBitmap: {
         contentType: 'image/png',
         name: 'ImageBitmap',
-        runtimeFormat: DataFormat.PNG
+        runtimeFormat: DataFormat.PNG,
+        immutable: true
     },
     ImageVector: {
         contentType: 'image/svg+xml',
         name: 'ImageVector',
-        runtimeFormat: DataFormat.SVG
+        runtimeFormat: DataFormat.SVG,
+        immutable: true
     },
     Project: {
         contentType: 'application/json',
         name: 'Project',
-        runtimeFormat: DataFormat.JSON
+        runtimeFormat: DataFormat.JSON,
+        immutable: false
     },
     Sound: {
         contentType: 'audio/x-wav',
         name: 'Sound',
-        runtimeFormat: DataFormat.WAV
+        runtimeFormat: DataFormat.WAV,
+        immutable: true
     },
     Sprite: {
         contentType: 'application/json',
         name: 'Sprite',
-        runtimeFormat: DataFormat.JSON
+        runtimeFormat: DataFormat.JSON,
+        immutable: true
     }
 };
 

src/BuiltinHelper.js

@@ -9,7 +9,7 @@ const Helper = require('./Helper');
  * @typedef {object} BuiltinAssetRecord
  * @property {AssetType} type - The type of the asset.
  * @property {DataFormat} format - The format of the asset's data.
- * @property {string} id - The asset's unique ID.
+ * @property {?string} id - The asset's unique ID.
  * @property {Buffer} data - The asset's data.
  */
 
@@ -97,8 +97,8 @@ class BuiltinHelper extends Helper {
     cache (assetType, dataFormat, data, id) {
         if (!dataFormat) throw new Error('Data cached without specifying its format');
         if (id) {
-            if (this.assets.hasOwnProperty(id)) return id;
-        } else {
+            if (this.assets.hasOwnProperty(id) && assetType.immutable) return id;
+        } else if (assetType.immutable) {
             const hash = crypto.createHash('md5');
             hash.update(data);
             id = hash.digest('hex');

src/ScratchStorage.js

@@ -117,11 +117,12 @@ class ScratchStorage {
                                     tryNextHelper();
                                 } else {
                                     // TODO? this.localHelper.cache(assetType, assetId, asset);
-                                    if (helper !== this.builtinHelper) {
+                                    if (helper !== this.builtinHelper && assetType.immutable) {
                                         asset.assetId = this.builtinHelper.cache(
                                             assetType,
                                             asset.dataFormat,
-                                            asset.data
+                                            asset.data,
+                                            assetId
                                         );
                                     }
                                     // Note that other attempts may have caused errors, effectively suppressed here.