fix(compiler): warn when inline-template component has no children (fix #6703) (#6715)

src/compiler/codegen/index.js

@@ -309,7 +309,7 @@ function genDirectives (el: ASTElement, state: CodegenState): string | void {
 function genInlineTemplate (el: ASTElement, state: CodegenState): ?string {
   const ast = el.children[0]
   if (process.env.NODE_ENV !== 'production' && (
-    el.children.length > 1 || ast.type !== 1
+    el.children.length !== 1 || ast.type !== 1
   )) {
     state.warn('Inline-template components must have exactly one child element.')
   }

test/unit/modules/compiler/codegen.spec.js

@@ -455,7 +455,14 @@ describe('codegen', () => {
       '<my-component inline-template><hr><hr></my-component>',
       `with(this){return _c('my-component',{inlineTemplate:{render:function(){with(this){return _c('hr')}},staticRenderFns:[]}})}`
     )
+    try {
+      assertCodegen(
+        '<my-component inline-template></my-component>',
+        ''
+      )
+    } catch (e) {}
     expect('Inline-template components must have exactly one child element.').toHaveBeenWarned()
+    expect(console.error.calls.count()).toBe(2)
   })
 
   it('generate static trees inside v-for', () => {