feat: warn when losing transparency during thumbnail generation (#26243)

* feat: preserve alpha

* refactor: use isTransparent naming and separate getImageMetadata

* warn instead of preserve

server/src/utils/mime-types.spec.ts

@@ -153,6 +153,33 @@ describe('mimeTypes', () => {
     }
   });
 
+  describe('canBeTransparent', () => {
+    for (const img of [
+      'a.avif',
+      'a.bmp',
+      'a.gif',
+      'a.heic',
+      'a.heif',
+      'a.hif',
+      'a.jxl',
+      'a.png',
+      'a.svg',
+      'a.tif',
+      'a.tiff',
+      'a.webp',
+    ]) {
+      it(`should return true for ${img}`, () => {
+        expect(mimeTypes.canBeTransparent(img)).toBe(true);
+      });
+    }
+
+    for (const img of ['a.jpg', 'a.jpeg', 'a.jpe', 'a.insp', 'a.jp2', 'a.cr3', 'a.dng', 'a.nef', 'a.arw']) {
+      it(`should return false for ${img}`, () => {
+        expect(mimeTypes.canBeTransparent(img)).toBe(false);
+      });
+    }
+  });
+
   describe('animated image', () => {
     for (const img of ['a.avif', 'a.gif', 'a.webp']) {
       it('should identify animated image mime types as such', () => {

server/src/utils/mime-types.ts

@@ -77,6 +77,21 @@ const extensionOverrides: Record<string, string> = {
   'image/jpeg': '.jpg',
 };
 
+const transparentCapableExtensions = new Set([
+  '.avif',
+  '.bmp',
+  '.gif',
+  '.heic',
+  '.heif',
+  '.hif',
+  '.jxl',
+  '.png',
+  '.svg',
+  '.tif',
+  '.tiff',
+  '.webp',
+]);
+
 const profileExtensions = new Set(['.avif', '.dng', '.heic', '.heif', '.jpeg', '.jpg', '.png', '.webp', '.svg']);
 const profile: Record<string, string[]> = Object.fromEntries(
   Object.entries(image).filter(([key]) => profileExtensions.has(key)),
@@ -134,6 +149,7 @@ export const mimeTypes = {
   isProfile: (filename: string) => isType(filename, profile),
   isSidecar: (filename: string) => isType(filename, sidecar),
   isVideo: (filename: string) => isType(filename, video),
+  canBeTransparent: (filename: string) => transparentCapableExtensions.has(extname(filename).toLowerCase()),
   isRaw: (filename: string) => isType(filename, raw),
   lookup,
   /** return an extension (including a leading `.`) for a mime-type */