From 07ae4deaf9255f88ca0d1a100c1dbaa566a8b188 Mon Sep 17 00:00:00 2001
From: Daniil Ovchinnikov <daniil.ovchinnikov@jetbrains.com>
Date: Tue, 17 Apr 2018 19:03:27 +0300
Subject: [PATCH] [lang] disallow MetaLanguage-s as base languages

No language can have MetaLanguage as its base language.
This implies that MetaLanguage-s cannot have dialects.
---
 .../src/com/intellij/lang/Language.java       | 24 +++++++------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/platform/core-api/src/com/intellij/lang/Language.java b/platform/core-api/src/com/intellij/lang/Language.java
index 0b06b6edf4aa..d849daa857d5 100644
--- a/platform/core-api/src/com/intellij/lang/Language.java
+++ b/platform/core-api/src/com/intellij/lang/Language.java
@@ -1,18 +1,4 @@
-/*
- * Copyright 2000-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.lang;
 
 import com.intellij.diagnostic.ImplementationConflictException;
@@ -71,6 +57,14 @@ public abstract class Language extends UserDataHolderBase {
   }
 
   protected Language(@Nullable Language baseLanguage, @NotNull String ID, @NotNull String... mimeTypes) {
+    if (baseLanguage instanceof MetaLanguage) {
+      throw new ImplementationConflictException(
+        "MetaLanguage cannot be a base language.\n" +
+        "This language: '" + ID + "'\n" +
+        "Base language: '" + baseLanguage.getID() + "'",
+        null, this, baseLanguage
+      );
+    }
     myBaseLanguage = baseLanguage;
     myID = ID;
     myMimeTypes = mimeTypes.length == 0 ? ArrayUtil.EMPTY_STRING_ARRAY : mimeTypes;