fix(ssr): forward helpers provided by CSS v-bind (#6489)

fix #6201

packages/compiler-ssr/__tests__/ssrInjectCssVars.spec.ts

@@ -1,3 +1,4 @@
+import { BindingTypes } from '@vue/compiler-dom'
 import { compile } from '../src'
 
 describe('ssr: inject <style vars>', () => {
@@ -111,4 +112,25 @@ describe('ssr: inject <style vars>', () => {
       }"
     `)
   })
+
+  test('inject helpers', () => {
+    const result = compile(`<div/>`, {
+      inline: true,
+      bindingMetadata: { dynamic: BindingTypes.SETUP_MAYBE_REF },
+      ssrCssVars: '{ "--hash": (dynamic) }'
+    })
+
+    expect(result.code).toMatchInlineSnapshot(`
+      "(_ctx, _push, _parent, _attrs) => {
+        const _cssVars = { style: { \\"--hash\\": (_unref(dynamic)) }}
+        _push(\`<div\${_ssrRenderAttrs(_mergeProps(_attrs, _cssVars))}></div>\`)
+      }"
+    `)
+    expect(result.ast.helpers).toMatchInlineSnapshot(`
+      Array [
+        Symbol(mergeProps),
+        Symbol(unref),
+      ]
+    `)
+  })
 })

packages/compiler-ssr/src/ssrCodegenTransform.ts

@@ -40,13 +40,17 @@ export function ssrCodegenTransform(ast: RootNode, options: CompilerOptions) {
   // we do this instead of inlining the expression to ensure the vars are
   // only resolved once per render
   if (options.ssrCssVars) {
+    const cssContext = createTransformContext(createRoot([]), options)
     const varsExp = processExpression(
       createSimpleExpression(options.ssrCssVars, false),
-      createTransformContext(createRoot([]), options)
+      cssContext
     )
     context.body.push(
       createCompoundExpression([`const _cssVars = { style: `, varsExp, `}`])
     )
+    Array.from(cssContext.helpers.keys()).forEach(helper =>
+      ast.helpers.push(helper)
+    )
   }
 
   const isFragment =