add cssHash option (#6026)

* Allow to customize the css scope class

* Pass component name to scope class generator

* Move Stylesheet arguments into an object

* Refactor to cssHash

* Please the almighty linter

* pass hash function to cssHash

* update test

* document cssHash option

Co-authored-by: Christian Kaisermann <christian@kaisermann.me>

site/content/docs/04-compile-time.md

@@ -74,6 +74,7 @@ The following options can be passed to the compiler. None are required:
 | `customElement` | `false` | If `true`, tells the compiler to generate a custom element constructor instead of a regular Svelte component.
 | `tag` | `null` | A `string` that tells Svelte what tag name to register the custom element with. It must be a lowercase alphanumeric string with at least one hyphen, e.g. `"my-element"`.
 | `css` | `true` | If `true`, styles will be included in the JavaScript class and injected at runtime. It's recommended that you set this to `false` and use the CSS that is statically generated, as it will result in smaller JavaScript bundles and better performance.
+| `cssHash` | See right | A function that takes a `{ hash, css, name, filename }` argument and returns the string that is used as a classname for scoped CSS. It defaults to returning `svelte-${hash(css)}`
 | `loopGuardTimeout` | 0 | A `number` that tells Svelte to break the loop if it blocks the thread for more than `loopGuardTimeout` ms. This is useful to prevent infinite loops. **Only available when `dev: true`**
 | `preserveComments` | `false` | If `true`, your HTML comments will be preserved during server-side rendering. By default, they are stripped out.
 | `preserveWhitespace` | `false` | If `true`, whitespace inside and between elements is kept as you typed it, rather than removed or collapsed to a single space where possible.

src/compiler/compile/Component.ts

@@ -133,12 +133,14 @@ export default class Component {
 		this.locate = getLocator(this.source, { offsetLine: 1 });
 
 		// styles
-		this.stylesheet = new Stylesheet(
+		this.stylesheet = new Stylesheet({
 			source,
 			ast,
-			compile_options.filename,
+			filename: compile_options.filename,
-			compile_options.dev
+			component_name: name,
-		);
+			dev: compile_options.dev,
+			get_css_hash: compile_options.cssHash
+		});
 		this.stylesheet.validate(this);
 
 		this.component_options = process_component_options(

src/compiler/compile/css/Stylesheet.ts

@@ -2,7 +2,7 @@ import MagicString from 'magic-string';
 import { walk } from 'estree-walker';
 import Selector from './Selector';
 import Element from '../nodes/Element';
-import { Ast } from '../../interfaces';
+import { Ast, CssHashGetter } from '../../interfaces';
 import Component from '../Component';
 import { CssNode } from './interfaces';
 import hash from '../utils/hash';
@@ -275,6 +275,10 @@ class Atrule {
 	}
 }
 
+const get_default_css_hash: CssHashGetter = ({ css, hash }) => {
+	return `svelte-${hash(css)}`;
+};
+
 export default class Stylesheet {
 	source: string;
 	ast: Ast;
@@ -289,14 +293,33 @@ export default class Stylesheet {
 
 	nodes_with_css_class: Set<CssNode> = new Set();
 
-	constructor(source: string, ast: Ast, filename: string, dev: boolean) {
+	constructor({
+		source,
+		ast,
+		component_name,
+		filename,
+		dev,
+		get_css_hash = get_default_css_hash
+	}: {
+		source: string;
+		ast: Ast;
+		filename: string | undefined;
+		component_name: string | undefined;
+		dev: boolean;
+		get_css_hash: CssHashGetter;
+	}) {
 		this.source = source;
 		this.ast = ast;
 		this.filename = filename;
 		this.dev = dev;
 
 		if (ast.css && ast.css.children.length) {
-			this.id = `svelte-${hash(ast.css.content.styles)}`;
+			this.id = get_css_hash({
+				filename,
+				name: component_name,
+				css: ast.css.content.styles,
+				hash
+			});
 
 			this.has_styles = true;
 

src/compiler/compile/index.ts

@@ -28,7 +28,8 @@ const valid_options = [
 	'css',
 	'loopGuardTimeout',
 	'preserveComments',
-	'preserveWhitespace'
+	'preserveWhitespace',
+	'cssHash'
 ];
 
 function validate_options(options: CompileOptions, warnings: Warning[]) {

src/compiler/interfaces.ts

@@ -104,6 +104,13 @@ export interface Warning {
 
 export type ModuleFormat = 'esm' | 'cjs';
 
+export type CssHashGetter = (args: {
+	name: string;
+	filename: string | undefined;
+	css: string;
+	hash: (input: string) => string;
+}) => string;
+
 export interface CompileOptions {
 	format?: ModuleFormat;
 	name?: string;
@@ -125,6 +132,7 @@ export interface CompileOptions {
 	css?: boolean;
 	loopGuardTimeout?: number;
 	namespace?: string;
+	cssHash?: CssHashGetter;
 
 	preserveComments?: boolean;
 	preserveWhitespace?: boolean;
@@ -166,7 +174,7 @@ export interface Var {
 	imported?: boolean;
 }
 
-export interface CssResult { 
+export interface CssResult {
 	code: string;
 	map: SourceMap;
 }

test/css/samples/custom-css-hash/_config.js

@@ -0,0 +1,12 @@
+export default {
+	compileOptions: {
+		filename: 'src/components/FooSwitcher.svelte',
+		cssHash({ hash, css, name, filename }) {
+			const minFilename = filename
+				.split('/')
+				.map(i => i.charAt(0).toLowerCase())
+				.join('');
+			return `sv-${name}-${minFilename}-${hash(css)}`;
+		}
+	}
+};

test/css/samples/custom-css-hash/expected.css

@@ -0,0 +1 @@
+div.sv-FooSwitcher-scf-bzh57p{color:red}

test/css/samples/custom-css-hash/input.svelte

@@ -0,0 +1,7 @@
+<div>red</div>
+
+<style>
+	div {
+		color: red;
+	}
+</style>