fix(compiler-core): fix v-if + v-for on <template>

fix #1637

packages/compiler-core/__tests__/transforms/__snapshots__/vFor.spec.ts.snap

@@ -180,6 +180,22 @@ return function render(_ctx, _cache) {
 }"
 `;
 
+exports[`compiler: v-for codegen v-if + v-for on <template> 1`] = `
+"const _Vue = Vue
+
+return function render(_ctx, _cache) {
+  with (_ctx) {
+    const { renderList: _renderList, Fragment: _Fragment, openBlock: _openBlock, createBlock: _createBlock, createCommentVNode: _createCommentVNode } = _Vue
+
+    return ok
+      ? (_openBlock(true), _createBlock(_Fragment, { key: 0 }, _renderList(list, (i) => {
+          return (_openBlock(), _createBlock(_Fragment, null, [], 64 /* STABLE_FRAGMENT */))
+        }), 256 /* UNKEYED_FRAGMENT */))
+      : _createCommentVNode(\\"v-if\\", true)
+  }
+}"
+`;
+
 exports[`compiler: v-for codegen value + key + index 1`] = `
 "const _Vue = Vue
 

packages/compiler-core/__tests__/transforms/vFor.spec.ts

@@ -840,6 +840,44 @@ describe('compiler: v-for', () => {
       expect(generate(root).code).toMatchSnapshot()
     })
 
+    // 1637
+    test('v-if + v-for on <template>', () => {
+      const {
+        root,
+        node: { codegenNode }
+      } = parseWithForTransform(`<template v-if="ok" v-for="i in list"/>`)
+      expect(codegenNode).toMatchObject({
+        type: NodeTypes.JS_CONDITIONAL_EXPRESSION,
+        test: { content: `ok` },
+        consequent: {
+          type: NodeTypes.VNODE_CALL,
+          props: createObjectMatcher({
+            key: `[0]`
+          }),
+          isBlock: true,
+          disableTracking: true,
+          patchFlag: genFlagText(PatchFlags.UNKEYED_FRAGMENT),
+          children: {
+            type: NodeTypes.JS_CALL_EXPRESSION,
+            callee: RENDER_LIST,
+            arguments: [
+              { content: `list` },
+              {
+                type: NodeTypes.JS_FUNCTION_EXPRESSION,
+                params: [{ content: `i` }],
+                returns: {
+                  type: NodeTypes.VNODE_CALL,
+                  tag: FRAGMENT,
+                  isBlock: true
+                }
+              }
+            ]
+          }
+        }
+      })
+      expect(generate(root).code).toMatchSnapshot()
+    })
+
     test('v-for on element with custom directive', () => {
       const {
         root,