fix(ssr): normalize class in child attrs (#4953)

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/child/expected.html

@@ -0,0 +1,8 @@
+<x-parent>
+  <template shadowrootmode="open">
+    <x-child class="button__icon">
+      <template shadowrootmode="open">
+      </template>
+    </x-child>
+  </template>
+</x-parent>

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/child/index.js

@@ -0,0 +1,3 @@
+export const tagName = 'x-parent';
+export { default } from 'x/parent';
+export * from 'x/parent';

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/child/modules/x/child/child.html

@@ -0,0 +1 @@
+<template></template>

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/child/modules/x/child/child.js

@@ -0,0 +1,5 @@
+import { LightningElement } from 'lwc';
+
+export default class extends LightningElement {
+
+}

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/child/modules/x/parent/parent.html

@@ -0,0 +1,3 @@
+<template>
+    <x-child class={computedClassNames}></x-child>
+</template>

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/child/modules/x/parent/parent.js

@@ -0,0 +1,9 @@
+import { LightningElement } from 'lwc';
+
+export default class CustomButton extends LightningElement {
+    get computedClassNames() {
+      return {
+        button__icon: true
+      }
+    }
+  }

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/component/expected.html

@@ -0,0 +1,8 @@
+<x-parent>
+  <template shadowrootmode="open">
+    <x-child class="button__icon">
+      <template shadowrootmode="open">
+      </template>
+    </x-child>
+  </template>
+</x-parent>

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/component/index.js

@@ -0,0 +1,3 @@
+export const tagName = 'x-parent';
+export { default } from 'x/parent';
+export * from 'x/parent';

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/component/modules/x/child/child.html

@@ -0,0 +1 @@
+<template></template>

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/component/modules/x/child/child.js

@@ -0,0 +1,5 @@
+import { LightningElement } from 'lwc';
+
+export default class extends LightningElement {
+
+}

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/component/modules/x/parent/parent.html

@@ -0,0 +1,3 @@
+<template>
+    <lwc:component lwc:is={ctor} class={computedClassNames}></lwc:component>
+</template>

packages/@lwc/engine-server/src/__tests__/fixtures/attribute-class/unstyled/component/modules/x/parent/parent.js

@@ -0,0 +1,11 @@
+import { LightningElement } from 'lwc';
+import xChild from 'x/child';
+
+export default class CustomButton extends LightningElement {
+  ctor = xChild;
+    get computedClassNames() {
+      return {
+        button__icon: true
+      }
+    }
+  }

packages/@lwc/ssr-compiler/src/compile-template/shared.ts

@@ -129,7 +129,13 @@ export function getChildAttrsOrProps(
 
                 return b.property('init', key, b.literal(type === 'Attribute' ? '' : value.value));
             } else if (value.type === 'Identifier' || value.type === 'MemberExpression') {
-                const propValue = expressionIrToEs(value, cxt);
+                let propValue = expressionIrToEs(value, cxt);
+
+                if (name === 'class') {
+                    cxt.import('normalizeClass');
+                    propValue = b.callExpression(b.identifier('normalizeClass'), [propValue]);
+                }
+
                 return b.property('init', key, propValue);
             }
             throw new Error(`Unimplemented child attr IR node type: ${value.type}`);