feat: update with RFC feedback

packages/astro/components/Image.astro

@@ -23,10 +23,11 @@ if (typeof props.height === 'string') {
 }
 
 const image = await getImage(props);
+
 const additionalAttributes: Record<string, any> = {};
 
-if (image.srcSet.length > 0) {
-	additionalAttributes.srcset = image.srcSetValue;
+if (image.srcSet.values.length > 0) {
+	additionalAttributes.srcset = image.srcSet.attribute;
 }
 ---
 

packages/astro/components/Picture.astro

@@ -6,17 +6,22 @@ import { AstroError, AstroErrorData } from '../dist/core/errors/index.js';
 import { HTMLAttributes } from '../types';
 
 type Props = (LocalImageProps | RemoteImageProps) & {
-	formats: ImageOutputFormat[];
-	fallbackFormat: ImageOutputFormat;
-	pictureAttributes: HTMLAttributes<'picture'>;
+	formats?: ImageOutputFormat[];
+	fallbackFormat?: ImageOutputFormat;
+	pictureAttributes?: HTMLAttributes<'picture'>;
 };
 
-const props = Astro.props;
-const optimizedImages: Record<
-	ImageOutputFormat,
-	GetImageResult
-> = await Promise.all(
-	props.formats.map(async (format) => await getImage({ ...props, format: format, widths: props.widths, densities: props.densities }))
+const {formats = ["webp"], pictureAttributes = {}, ...props} = Astro.props;
+
+if (props.alt === undefined || props.alt === null) {
+	throw new AstroError(AstroErrorData.ImageMissingAlt);
+}
+
+const optimizedImages: GetImageResult[] = await Promise.all(
+	formats.map(
+		async (format) =>
+			await getImage({ ...props, format: format, widths: props.widths, densities: props.densities })
+	)
 );
 
 const fallbackFormat =
@@ -26,19 +31,24 @@ const fallbackFormat =
 			: 'png'
 		: 'png';
 
-const originalImage = await getImage({ ...props, format: fallbackFormat, widths: props.widths, densities: props.densities });
+const fallbackImage = await getImage({
+	...props,
+	format: fallbackFormat,
+	widths: props.widths,
+	densities: props.densities,
+});
 
-if (props.alt === undefined || props.alt === null) {
-	throw new AstroError(AstroErrorData.ImageMissingAlt);
+const additionalAttributes: Record<string, any> = {};
+if (fallbackImage.srcSet.values.length > 0) {
+	additionalAttributes.srcset = fallbackImage.srcSet.attribute;
 }
 ---
 
-<picture {...props.pictureAttributes}>
-	{Object.entries(optimizedImages).map(([format, image]) => (
-		<source
-			srcset={image.srcSetValue}
-			type={image.srcSet[0].attributes?.type}
-		/>
-	))}
-	<img src={originalImage.src} {...originalImage.attributes} />
+<picture {...pictureAttributes}>
+	{
+		Object.entries(optimizedImages).map(([_, image]) => (
+			<source srcset={`${image.src}, ` + image.srcSet.attribute} type={image.srcSet.values[0].attributes?.type} />
+		))
+	}
+	<img src={fallbackImage.src} {...additionalAttributes} {...fallbackImage.attributes} />
 </picture>

packages/astro/src/assets/internal.ts

@@ -124,8 +124,10 @@ export async function getImage(
 		rawOptions: resolvedOptions,
 		options: validatedOptions,
 		src: imageURL,
-		srcSet: srcSets,
-		srcSetValue: srcSets.map((srcSet) => `${srcSet.url} ${srcSet.descriptor}`).join(', '),
+		srcSet: {
+			values: srcSets,
+			attribute: srcSets.map((srcSet) => `${srcSet.url} ${srcSet.descriptor}`).join(', '),
+		},
 		attributes:
 			service.getHTMLAttributes !== undefined
 				? service.getHTMLAttributes(validatedOptions, imageConfig)

packages/astro/src/assets/services/service.ts

@@ -188,8 +188,7 @@ export const baseService: Omit<LocalImageService, 'transform'> = {
 			}
 
 			if (options.widths && options.densities) {
-				console.warn('Cannot use `widths` and `densities` at the same time. Using `densities`.');
-				options.widths = undefined;
+				throw new AstroError(AstroErrorData.IncompatibleDescriptorOptions);
 			}
 
 			// We currently do not support processing SVGs, so whenever the input format is a SVG, force the output to also be one
@@ -226,6 +225,9 @@ export const baseService: Omit<LocalImageService, 'transform'> = {
 		const targetFormat = options.format ?? DEFAULT_OUTPUT_FORMAT;
 
 		const aspectRatio = targetWidth / targetHeight;
+		const imageWidth = isESMImportedImage(options.src) ? options.src.width : options.width;
+		const maxWidth = options.width ?? imageWidth ?? Infinity;
+
 		if (densities) {
 			const densityValues = densities.map((density) => {
 				if (typeof density === 'number') {
@@ -235,14 +237,17 @@ export const baseService: Omit<LocalImageService, 'transform'> = {
 				}
 			});
 
-			const densityWidths = densityValues.map((density) => Math.round(targetWidth * density));
+			const densityWidths = densityValues
+				.sort()
+				.map((density) => Math.round(targetWidth * density));
 
 			densityWidths.forEach((width, index) => {
+				const maxTargetWidth = Math.min(width, maxWidth);
 				srcSet.push({
 					transform: {
 						...options,
-						width,
-						height: Math.round(width / aspectRatio),
+						width: maxTargetWidth,
+						height: Math.round(maxTargetWidth / aspectRatio),
 						format: targetFormat,
 					},
 					descriptor: `${densityValues[index]}x`,
@@ -253,11 +258,12 @@ export const baseService: Omit<LocalImageService, 'transform'> = {
 			});
 		} else if (widths) {
 			widths.forEach((width) => {
+				const maxTargetWidth = Math.min(width, maxWidth);
 				srcSet.push({
 					transform: {
 						...options,
 						width,
-						height: Math.round(width / aspectRatio),
+						height: Math.round(maxTargetWidth / aspectRatio),
 						format: targetFormat,
 					},
 					descriptor: `${width}w`,

packages/astro/src/assets/types.ts

@@ -59,8 +59,10 @@ export interface GetImageResult {
 	rawOptions: ImageTransform;
 	options: ImageTransform;
 	src: string;
-	srcSet: SrcSetValue[];
-	srcSetValue: string;
+	srcSet: {
+		values: SrcSetValue[];
+		attribute: string;
+	};
 	attributes: Record<string, any>;
 }
 

packages/astro/src/assets/utils/transformToPath.ts

@@ -16,8 +16,8 @@ export function propsToFilename(transform: ImageTransform, hash: string) {
 }
 
 export function hashTransform(transform: ImageTransform, imageService: string) {
-	// take everything from transform except alt, which is not used in the hash
-	const { alt, ...rest } = transform;
+	// Extract the fields we want to hash
+	const { alt, class: className, style, ...rest } = transform;
 	const hashFields = { ...rest, imageService };
 	return shorthash(JSON.stringify(hashFields));
 }

packages/astro/src/core/errors/errors-data.ts

@@ -621,6 +621,21 @@ export const ExpectedImageOptions = {
 		`Expected getImage() parameter to be an object. Received \`${options}\`.`,
 } satisfies ErrorData;
 
+/**
+ * @docs
+ * @see
+ * - [Images](https://docs.astro.build/en/guides/images/)
+ * @description
+ * Only one of `densities` or `widths` can be specified. Those attributes are used to construct a `srcset` attribute, which cannot have both `x` and `w` descriptors.
+ */
+export const IncompatibleDescriptorOptions = {
+	name: 'IncompatibleDescriptorOptions',
+	title: 'Cannot set both `densities` and `widths`',
+	message:
+		"Only one of `densities` or `widths` can be specified. In most cases, you'll probably want to use only `widths` if you require specific widths.",
+	hint: 'Those attributes are used to construct a `srcset` attribute, which cannot have both `x` and `w` descriptors.',
+} satisfies ErrorData;
+
 /**
  * @docs
  * @see