feat(core): support v-show directive (#310)

packages/compiler-dom/__tests__/transforms/__snapshots__/vShow.spec.ts.snap

@@ -0,0 +1,15 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`compiler: v-show transform simple expression 1`] = `
+"const _Vue = Vue
+
+return function render() {
+  with (this) {
+    const { vShow: _vShow, createVNode: _createVNode, withDirectives: _withDirectives, createBlock: _createBlock, openBlock: _openBlock } = _Vue
+    
+    return (_openBlock(), _withDirectives(_createBlock(\\"div\\", null, null, 32 /* NEED_PATCH */), [
+      [_vShow, a]
+    ]))
+  }
+}"
+`;

packages/compiler-dom/__tests__/transforms/vShow.spec.ts

@@ -0,0 +1,36 @@
+import { parse, transform, generate, CompilerOptions } from '@vue/compiler-core'
+import { transformElement } from '../../../compiler-core/src/transforms/transformElement'
+import { transformShow } from '../../src/transforms/vShow'
+import { DOMErrorCodes } from '../../src/errors'
+
+function transformWithShow(template: string, options: CompilerOptions = {}) {
+  const ast = parse(template)
+  transform(ast, {
+    nodeTransforms: [transformElement],
+    directiveTransforms: {
+      show: transformShow
+    },
+    ...options
+  })
+  return ast
+}
+
+describe('compiler: v-show transform', () => {
+  test('simple expression', () => {
+    const ast = transformWithShow(`<div v-show="a"/>`)
+
+    expect(generate(ast).code).toMatchSnapshot()
+  })
+
+  test('should raise error if has no expression', () => {
+    const onError = jest.fn()
+    transformWithShow(`<div v-show/>`, { onError })
+
+    expect(onError).toHaveBeenCalledTimes(1)
+    expect(onError).toHaveBeenCalledWith(
+      expect.objectContaining({
+        code: DOMErrorCodes.X_V_SHOW_NO_EXPRESSION
+      })
+    )
+  })
+})