[WIP] feat: Provide installation instructions on missing language preprocessors

lib/compileTemplate.ts

@@ -40,6 +40,16 @@ export function compileTemplate (
     return actuallyCompile(Object.assign({}, options, {
       source: preprocess(options, preprocessor)
     }))
+  } else if (preprocessLang) {
+    return {
+      code: (
+        `var render = function () {}\n` +
+        `var staticRenderFns = []\n`
+      ),
+      source: options.source,
+      tips: [`Component ${options.filename} uses lang ${preprocessLang} for template. Please install the language preprocessor.`],
+      errors: [`Component ${options.filename} uses lang ${preprocessLang} for template, however it is not installed.`]
+    };
   } else {
     return actuallyCompile(options)
   }

test/compileTemplate.spec.ts

@@ -0,0 +1,45 @@
+import { parse } from '../lib/parse'
+import { compileTemplate } from '../lib/compileTemplate'
+import * as compiler from 'vue-template-compiler'
+
+test('preprocess pug', () => {
+  const template = parse({
+    source:
+      '<template lang="pug">\n' +
+      'body\n' +
+      ' h1 Pug Examples\n' +
+      ' div.container\n' +
+      '   p Cool Pug example!\n' +
+      '</template>\n',
+    filename: 'example.vue',
+    needMap: true
+  }).template
+
+  const result = compileTemplate({
+    filename: 'example.vue',
+    source: template.content,
+    preprocessLang: template.lang,
+    compiler: compiler
+  })
+
+  expect(result.errors.length).toBe(0)
+})
+
+test('warn missing preprocessor', () => {
+  const template = parse({
+    source:
+      '<template lang="unknownLang">\n' +
+      '</template>\n',
+    filename: 'example.vue',
+    needMap: true
+  }).template
+
+  const result = compileTemplate({
+    filename: 'example.vue',
+    source: template.content,
+    preprocessLang: template.lang,
+    compiler: compiler
+  })
+
+  expect(result.errors.length).toBe(1)
+})