fix(compiler-core): consistently remove comment nodes for pre tags in production

close #2217

packages/compiler-core/__tests__/parse.spec.ts

@@ -384,6 +384,25 @@ describe('compiler: parse', () => {
       expect(astNoComment.children).toHaveLength(0)
       expect(astWithComments.children).toHaveLength(1)
     })
+
+    // #2217
+    test('comments in the <pre> tag should be removed in production mode', () => {
+      __DEV__ = false
+      const rawText = `<p/><!-- foo --><p/>`
+      const ast = baseParse(`<pre>${rawText}</pre>`)
+      __DEV__ = true
+
+      expect((ast.children[0] as ElementNode).children).toMatchObject([
+        {
+          type: NodeTypes.ELEMENT,
+          tag: 'p'
+        },
+        {
+          type: NodeTypes.ELEMENT,
+          tag: 'p'
+        }
+      ])
+    })
   })
 
   describe('Element', () => {

packages/compiler-core/src/parse.ts

@@ -198,10 +198,9 @@ function parseChildren(
   // (same as v2 whitespace: 'condense')
   let removedWhitespace = false
   if (mode !== TextModes.RAWTEXT) {
-    if (!context.inPre) {
     for (let i = 0; i < nodes.length; i++) {
       const node = nodes[i]
-        if (node.type === NodeTypes.TEXT) {
+      if (!context.inPre && node.type === NodeTypes.TEXT) {
         if (!/[^\t\r\n\f ]/.test(node.content)) {
           const prev = nodes[i - 1]
           const next = nodes[i + 1]
@@ -229,17 +228,18 @@ function parseChildren(
         } else {
           node.content = node.content.replace(/[\t\r\n\f ]+/g, ' ')
         }
-        } else if (
+      }
+      // also remove comment nodes in prod by default
+      if (
         !__DEV__ &&
         node.type === NodeTypes.COMMENT &&
         !context.options.comments
       ) {
-          // remove comment nodes in prod by default
         removedWhitespace = true
         nodes[i] = null as any
       }
     }
-    } else if (parent && context.options.isPreTag(parent.tag)) {
+    if (context.inPre && parent && context.options.isPreTag(parent.tag)) {
       // remove leading newline per html spec
       // https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
       const first = nodes[0]