Fixes #260

src/global-options.js

@@ -54,7 +54,7 @@ const DEFAULTS = {
   statsOnly: false,
   remoteImageMetadata: {}, // For `statsOnly` remote images, this needs to be populated with { width, height, format? }
 
-  useCache: true, // in-memory cache
+  useCache: true, // in-memory and disk cache
   dryRun: false, // Also returns a buffer instance in the return object. Doesn’t write anything to the file system
 
   hashLength: 10, // Truncates the hash to this length

src/image.js

@@ -32,6 +32,11 @@ const FORMAT_ALIASES = {
   "svg+xml": "svg",
 };
 
+const ANIMATED_TYPES = [
+  "webp",
+  "gif",
+];
+
 
 class Image {
   #input;
@@ -185,7 +190,7 @@ class Image {
     return valid.sort((a, b) => a - b);
   }
 
-  static getFormatsArray(formats, autoFormat, svgShortCircuit) {
+  static getFormatsArray(formats, autoFormat, svgShortCircuit, isAnimated) {
     if(formats && formats.length) {
       if(typeof formats === "string") {
         formats = formats.split(",");
@@ -216,6 +221,17 @@ class Image {
         });
       }
 
+      if(isAnimated) {
+        let validAnimatedFormats = formats.filter(f => ANIMATED_TYPES.includes(f));
+        // override formats if a valid animated format is found, otherwise leave as-is
+        if(validAnimatedFormats.length > 0) {
+          debug("Filtering non-animated formats from output: from %o to %o", formats, validAnimatedFormats);
+          formats = validAnimatedFormats;
+        } else {
+          debug("No animated output formats found for animated image, using static image instead.");
+        }
+      }
+
       // Remove duplicates (e.g., if null happens to coincide with an explicit format
       // or a user passes in multiple duplicate values)
       formats = [...new Set(formats)];
@@ -426,11 +442,18 @@ class Image {
     return orientation >= 5 && orientation <= 8;
   }
 
+  isAnimated(metadata, options) {
+    // input has multiple pages: https://sharp.pixelplumbing.com/api-input#metadata
+    // sharp options have animated image support enabled
+    return metadata?.pages > 1 && options?.sharpOptions?.animated;
+  }
+
   // metadata so far: width, height, format
   // src is used to calculate the output file names
   getFullStats(metadata) {
     let results = [];
-    let outputFormats = Image.getFormatsArray(this.options.formats, metadata.format || this.options.overrideInputFormat, this.options.svgShortCircuit);
+    let isImageAnimated = this.isAnimated(metadata, this.options);
+    let outputFormats = Image.getFormatsArray(this.options.formats, metadata.format || this.options.overrideInputFormat, this.options.svgShortCircuit, isImageAnimated);
 
     if (this.needsRotation(metadata.orientation)) {
       [metadata.height, metadata.width] = [metadata.width, metadata.height];

test/test.js

@@ -1065,6 +1065,7 @@ test("Animated gif", async t => {
     sharpOptions: {
       animated: true
     },
+    useCache: false,
     outputDir: "./test/img/",
   });
 
@@ -1075,6 +1076,42 @@ test("Animated gif", async t => {
   t.true( stats.gif[0].size > 1000*999 );
 });
 
+test("Animated gif format filtering (no good ones)", async t => {
+  let stats = await eleventyImage("./test/earth-animated.gif", {
+    dryRun: true,
+    formats: ["jpeg"],
+    sharpOptions: {
+      animated: true
+    },
+    useCache: false,
+  });
+
+  t.deepEqual(Object.keys(stats), ["jpeg"]);
+  t.is(stats.jpeg.length, 1);
+  t.is(stats.jpeg[0].width, 400);
+  t.is(stats.jpeg[0].height, 400);
+  // it’s a big boi
+  t.true( stats.jpeg[0].size < 1000*999, `${stats.jpeg[0].size} size is too big, should be smaller than ${1000*999}.` );
+});
+
+test("Animated gif format filtering (one valid one)", async t => {
+  let stats = await eleventyImage("./test/earth-animated.gif", {
+    dryRun: true,
+    formats: ["jpeg", "gif"],
+    sharpOptions: {
+      animated: true
+    },
+    useCache: false,
+  });
+
+  t.deepEqual(Object.keys(stats), ["gif"]);
+  t.is(stats.gif.length, 1);
+  t.is(stats.gif[0].width, 400);
+  t.is(stats.gif[0].height, 400);
+  // it’s a big boi
+  t.true( stats.gif[0].size > 1000*999 );
+});
+
 test("Change hashLength", async t => {
   let stats = await eleventyImage("./test/bio-2017.jpg", {
     widths: [null],