Added: informational error message on getting Android drawable folder… (#17751)

Summary:
… suffix for asset

Better informational error message on getting Android drawable folder suffix error using the asset name scale.

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I've got an not well described error when trying to bundle my React Native project package.

You can test the React Native bundle command like this:

node node_modules/react-native/local-cli/cli.js bundle --platform android --dev false --reset-cache --entry-file index.android.js --bundle-output /project/android/app/build/intermediates/assets/release/index.android.bundle --assets-dest /project/android/app/build

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/react-native-website, and link to your PR here.)

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  CATEGORY
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[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAL  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
[ IOS      ]   [ FEATURE     ]   [ {Directory} ]   |-----------|
[ ANDROID  ]   [ MINOR       ]   [ {Framework} ] - | {Message} |
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[CATEGORY] [TYPE] [LOCATION] - MESSAGE

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 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
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Pull Request resolved: https://github.com/facebook/react-native/pull/17751

Differential Revision: D13840597

Pulled By: cpojer

fbshipit-source-id: f755ef665b76ce3dd9c96e575fbc71e9aaf43a44

Libraries/Image/assetPathUtils.js

@@ -12,26 +12,25 @@
 
 import type {PackagerAsset} from './AssetRegistry';
 
+const androidScaleSuffix = {
+  '0.75': 'ldpi',
+  '1': 'mdpi',
+  '1.5': 'hdpi',
+  '2': 'xhdpi',
+  '3': 'xxhdpi',
+  '4': 'xxxhdpi',
+};
+
 /**
  * FIXME: using number to represent discrete scale numbers is fragile in essence because of
  * floating point numbers imprecision.
  */
 function getAndroidAssetSuffix(scale: number): string {
-  switch (scale) {
-    case 0.75:
-      return 'ldpi';
-    case 1:
-      return 'mdpi';
-    case 1.5:
-      return 'hdpi';
-    case 2:
-      return 'xhdpi';
-    case 3:
-      return 'xxhdpi';
-    case 4:
-      return 'xxxhdpi';
+  if (scale.toString() in androidScaleSuffix) {
+    return androidScaleSuffix[scale.toString()];
   }
-  throw new Error('no such scale');
+
+  throw new Error('no such scale ' + scale.toString());
 }
 
 // See https://developer.android.com/guide/topics/resources/drawable-resource.html
@@ -52,8 +51,12 @@ function getAndroidResourceFolderName(asset: PackagerAsset, scale: number) {
   var suffix = getAndroidAssetSuffix(scale);
   if (!suffix) {
     throw new Error(
-      "Don't know which android drawable suffix to use for asset: " +
-        JSON.stringify(asset),
+      "Don't know which android drawable suffix to use for scale: " +
+        scale +
+        '\nAsset: ' +
+        JSON.stringify(asset, null, '\t') +
+        '\nPossible scales are:' +
+        JSON.stringify(androidScaleSuffix, null, '\t'),
     );
   }
   const androidFolder = 'drawable-' + suffix;