feat: Svelte 5 fixes and improvements (#2217)

- pass children to zero types Svelte 5: +layout.svelte children not included in zero-effort type safety #2212
- add possibility to pass in version to svelte2tsx to differentiate transpiler targets
- add implicit children prop in Svelte 5 mode Svelte 5: Implicit children not detected correctly #2211
- add best-effort fallback typings to $props() rune
- hide deprecation warnings in generated code Svelte 5: Typescript generics in components are marked as deprecated svelte#9586

Author: dummdidumm

packages/language-server/src/plugins/svelte/SveltePlugin.ts

@@ -68,6 +68,7 @@ export class SveltePlugin
     async getCompiledResult(document: Document): Promise<SvelteCompileResult | null> {
         try {
             const svelteDoc = await this.getSvelteDoc(document);
+            // @ts-ignore is 'client' in Svelte 5
             return svelteDoc.getCompiledWith({ generate: 'dom' });
         } catch (error) {
             return null;

packages/language-server/src/plugins/typescript/DocumentSnapshot.ts

@@ -68,6 +68,7 @@ export interface DocumentSnapshot extends ts.IScriptSnapshot, DocumentMapper {
  */
 export interface SvelteSnapshotOptions {
     parse: typeof import('svelte/compiler').parse | undefined;
+    version: string | undefined;
     transformOnTemplateError: boolean;
     typingsNamespace: string;
 }
@@ -199,6 +200,7 @@ function preprocessSvelteFile(document: Document, options: SvelteSnapshotOptions
     try {
         const tsx = svelte2tsx(text, {
             parse: options.parse,
+            version: options.version,
             filename: document.getFilePath() ?? undefined,
             isTsFile: scriptKind === ts.ScriptKind.TS,
             mode: 'ts',

packages/language-server/src/plugins/typescript/features/DiagnosticsProvider.ts

@@ -42,7 +42,8 @@ export enum DiagnosticCode {
     MISSING_PROP = 2741, // "Property '..' is missing in type '..' but required in type '..'."
     NO_OVERLOAD_MATCHES_CALL = 2769, // "No overload matches this call"
     CANNOT_FIND_NAME = 2304, // "Cannot find name 'xxx'"
-    EXPECTED_N_ARGUMENTS = 2554 // Expected {0} arguments, but got {1}.
+    EXPECTED_N_ARGUMENTS = 2554, // Expected {0} arguments, but got {1}.
+    DEPRECATED_SIGNATURE = 6387 // The signature '..' of '..' is deprecated
 }
 
 export class DiagnosticsProviderImpl implements DiagnosticsProvider {
@@ -222,6 +223,8 @@ function hasNoNegativeLines(diagnostic: Diagnostic): boolean {
     return diagnostic.range.start.line >= 0 && diagnostic.range.end.line >= 0;
 }
 
+const generatedVarRegex = /'\$\$_\w+(\.\$on)?'/;
+
 function isNoFalsePositive(document: Document, tsDoc: SvelteDocumentSnapshot) {
     const text = document.getText();
     const usesPug = document.getLanguageAttribute('template') === 'pug';
@@ -238,6 +241,14 @@ function isNoFalsePositive(document: Document, tsDoc: SvelteDocumentSnapshot) {
             }
         }
 
+        if (
+            diagnostic.code === DiagnosticCode.DEPRECATED_SIGNATURE &&
+            generatedVarRegex.test(diagnostic.message)
+        ) {
+            // Svelte 5: $on and constructor is deprecated, but we don't want to show this warning for generated code
+            return false;
+        }
+
         return (
             isNoUsedBeforeAssigned(diagnostic, text, tsDoc) &&
             (!usesPug || isNoPugFalsePositive(diagnostic, document))

packages/language-server/src/plugins/typescript/service.ts

@@ -298,6 +298,7 @@ async function createLanguageService(
     let languageService = ts.createLanguageService(host);
     const transformationConfig: SvelteSnapshotOptions = {
         parse: svelteCompiler?.parse,
+        version: svelteCompiler?.VERSION,
         transformOnTemplateError: docContext.transformOnTemplateError,
         typingsNamespace: raw?.svelteOptions?.namespace || 'svelteHTML'
     };

packages/language-server/test/plugins/typescript/features/diagnostics/fixtures/component-invalid/components.d.ts

@@ -10,5 +10,9 @@ export class Works2 extends SvelteComponentTyped<
         };
     }
 > {}
-export class Works3 extends SvelteComponentTyped<any, { [evt: string]: CustomEvent<any> }, never> {}
+export class Works3 extends SvelteComponentTyped<
+    any,
+    { [evt: string]: CustomEvent<any> },
+    Record<string, never>
+> {}
 export class DoesntWork {}

packages/svelte2tsx/index.d.ts

@@ -79,6 +79,11 @@ export function svelte2tsx(
          * The Svelte parser to use. Defaults to the one bundled with `svelte2tsx`.
          */
         parse?: typeof import('svelte/compiler').parse;
+        /**
+         * The VERSION from 'svelte/compiler'. Defaults to the one bundled with `svelte2tsx`.
+         * Transpiled output may vary between versions.
+         */
+        version?: string;
     }
 ): SvelteCompiledToTsx
 

packages/svelte2tsx/repl/debug.ts

@@ -1,7 +1,10 @@
 import fs from 'fs';
 import { svelte2tsx } from '../src/svelte2tsx/index';
+import { VERSION } from 'svelte/compiler';
+
 const content = fs.readFileSync(`${__dirname}/index.svelte`, 'utf-8');
-console.log(svelte2tsx(content).code);
+
+console.log(svelte2tsx(content, {version: VERSION}).code);
 /**
  * To enable the REPL, simply run the "dev" package script.
  *

packages/svelte2tsx/src/htmlxtojsx_v2/index.ts

@@ -26,7 +26,7 @@ import { handleSpread } from './nodes/Spread';
 import { handleStyleDirective } from './nodes/StyleDirective';
 import { handleText } from './nodes/Text';
 import { handleTransitionDirective } from './nodes/Transition';
-import { handleSnippet } from './nodes/SnippetBlock';
+import { handleImplicitChildren, handleSnippet } from './nodes/SnippetBlock';
 import { handleRenderTag } from './nodes/RenderTag';
 
 type Walker = (node: TemplateNode, parent: BaseNode, prop: string, index: number) => void;
@@ -48,7 +48,11 @@ export function convertHtmlxToJsx(
     ast: TemplateNode,
     onWalk: Walker = null,
     onLeave: Walker = null,
-    options: { preserveAttributeCase?: boolean; typingsNamespace?: string } = {}
+    options: {
+        svelte5Plus: boolean;
+        preserveAttributeCase?: boolean;
+        typingsNamespace?: string;
+    } = { svelte5Plus: false }
 ) {
     const htmlx = str.original;
     options = { preserveAttributeCase: false, ...options };
@@ -114,6 +118,9 @@ export function convertHtmlxToJsx(
                         } else {
                             element = new InlineComponent(str, node);
                         }
+                        if (options.svelte5Plus) {
+                            handleImplicitChildren(node, element as InlineComponent);
+                        }
                         break;
                     case 'Element':
                     case 'Options':
@@ -248,6 +255,7 @@ export function htmlx2jsx(
         emitOnTemplateError?: boolean;
         preserveAttributeCase: boolean;
         typingsNamespace: string;
+        svelte5Plus: boolean;
     }
 ) {
     const ast = parseHtmlx(htmlx, parse, { ...options }).htmlxAst;

packages/svelte2tsx/src/htmlxtojsx_v2/nodes/SnippetBlock.ts

@@ -28,7 +28,7 @@ import { surroundWithIgnoreComments } from '../../utils/ignore';
 export function handleSnippet(
     str: MagicString,
     snippetBlock: BaseNode,
-    element?: InlineComponent
+    component?: InlineComponent
 ): void {
     const endSnippet = str.original.lastIndexOf('{', snippetBlock.end - 1);
     // Return something to silence the "snippet type not assignable to return type void" error
@@ -39,7 +39,7 @@ export function handleSnippet(
     const startEnd =
         str.original.indexOf('}', snippetBlock.context?.end || snippetBlock.expression.end) + 1;
 
-    if (element !== undefined) {
+    if (component !== undefined) {
         str.overwrite(snippetBlock.start, snippetBlock.expression.start, '', { contentOnly: true });
         const transforms: TransformationArray = ['('];
         if (snippetBlock.context) {
@@ -53,7 +53,10 @@ export function handleSnippet(
         }
         transforms.push(') => {');
         transforms.push([startEnd, snippetBlock.end]);
-        element.addProp([[snippetBlock.expression.start, snippetBlock.expression.end]], transforms);
+        component.addProp(
+            [[snippetBlock.expression.start, snippetBlock.expression.end]],
+            transforms
+        );
     } else {
         const generic = snippetBlock.context
             ? snippetBlock.context.typeAnnotation
@@ -79,3 +82,45 @@ export function handleSnippet(
         transform(str, snippetBlock.start, startEnd, startEnd, transforms);
     }
 }
+
+export function handleImplicitChildren(componentNode: BaseNode, component: InlineComponent): void {
+    if (componentNode.children?.length === 0) {
+        return;
+    }
+
+    let hasSlot = false;
+
+    for (const child of componentNode.children) {
+        if (
+            child.type === 'SvelteSelf' ||
+            child.type === 'InlineComponent' ||
+            child.type === 'Element' ||
+            child.type === 'SlotTemplate'
+        ) {
+            if (
+                child.attributes.some(
+                    (a) =>
+                        a.type === 'Attribute' &&
+                        a.name === 'slot' &&
+                        a.value[0]?.data !== 'default'
+                )
+            ) {
+                continue;
+            }
+        }
+        if (child.type === 'Text' && child.data.trim() === '') {
+            continue;
+        }
+        if (child.type !== 'SnippetBlock') {
+            hasSlot = true;
+            break;
+        }
+    }
+
+    if (!hasSlot) {
+        return;
+    }
+
+    // it's enough to fake a children prop, we don't need to actually move the content inside (which would also reset control flow)
+    component.addProp(['children'], ['() => { return __sveltets_2_any(0); }']);
+}

packages/svelte2tsx/src/svelte2tsx/createRenderFunction.ts

@@ -12,6 +12,7 @@ export interface CreateRenderFunctionPara extends InstanceScriptProcessResult {
     slots: Map<string, Map<string, string>>;
     events: ComponentEvents;
     uses$$SlotsInterface: boolean;
+    svelte5Plus: boolean;
     mode?: 'ts' | 'dts';
 }
 
@@ -28,6 +29,7 @@ export function createRenderFunction({
     uses$$slots,
     uses$$SlotsInterface,
     generics,
+    svelte5Plus,
     mode
 }: CreateRenderFunctionPara) {
     const htmlx = str.original;
@@ -105,19 +107,28 @@ export function createRenderFunction({
         : '{' +
           Array.from(slots.entries())
               .map(([name, attrs]) => {
-                  const attrsAsString = Array.from(attrs.entries())
-                      .map(([exportName, expr]) =>
-                          exportName.startsWith('__spread__')
-                              ? `...${expr}`
-                              : `${exportName}:${expr}`
-                      )
-                      .join(', ');
-                  return `'${name}': {${attrsAsString}}`;
+                  return `'${name}': {${slotAttributesToString(attrs)}}`;
               })
               .join(', ') +
           '}';
 
+    const needsImplicitChildrenProp =
+        svelte5Plus &&
+        !exportedNames.uses$propsRune() &&
+        slots.has('default') &&
+        !exportedNames.getExportsMap().has('default');
+    if (needsImplicitChildrenProp) {
+        exportedNames.addImplicitChildrenExport(slots.get('default')!.size > 0);
+    }
+
     const returnString =
+        `${
+            needsImplicitChildrenProp && slots.get('default')!.size > 0
+                ? `\nlet $$implicit_children = __sveltets_2_snippet({${slotAttributesToString(
+                      slots.get('default')!
+                  )}});`
+                : ''
+        }` +
         `\nreturn { props: ${exportedNames.createPropsStr(uses$$props || uses$$restProps)}` +
         `, slots: ${slotsAsDef}` +
         `, events: ${events.toDefString()} }}`;
@@ -127,3 +138,11 @@ export function createRenderFunction({
 
     str.append(returnString);
 }
+
+function slotAttributesToString(attrs: Map<string, string>) {
+    return Array.from(attrs.entries())
+        .map(([exportName, expr]) =>
+            exportName.startsWith('__spread__') ? `...${expr}` : `${exportName}:${expr}`
+        )
+        .join(', ');
+}