platform: make lang substitutor dynamic IDEA-226264

GitOrigin-RevId: 53f525ee77d1391b04a32632e36c258f71c98ba4

java/java-tests/testSrc/com/intellij/lang/LanguageSubstitutorLoadUnloadTest.kt

@@ -0,0 +1,43 @@
+// Copyright 2000-2019 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.ide.plugins.loadExtensionWithText
+import com.intellij.lang.java.JavaLanguage
+import com.intellij.openapi.fileTypes.PlainTextLanguage
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.util.Disposer
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.psi.LanguageSubstitutor
+import com.intellij.psi.PsiManager
+import com.intellij.testFramework.UsefulTestCase
+import com.intellij.testFramework.fixtures.LightJavaCodeInsightFixtureTestCase
+
+class LanguageSubstitutorLoadUnloadTest : LightJavaCodeInsightFixtureTestCase() {
+  
+  fun testBefore() {
+    myFixture.configureByText("dummy.txt", "package hello;")
+  }
+  
+  fun testLoadUnload() {
+    val beforeLoading = myFixture.configureByText("dummy.txt", "package hello;")
+    UsefulTestCase.assertInstanceOf(beforeLoading.language, PlainTextLanguage::class.java)
+    
+    val virtualFile = beforeLoading.virtualFile
+    val text = "<lang.substitutor language=\"TEXT\" implementationClass=\"${TextToJavaSubstitutor::class.java.name}\"/>"
+    val disposable = loadExtensionWithText(text, javaClass.classLoader)
+    val psiManager = PsiManager.getInstance(myFixture.project)
+    val afterLoading = psiManager.findFile(virtualFile)
+    UsefulTestCase.assertInstanceOf(afterLoading!!.language, JavaLanguage::class.java)
+    
+    Disposer.dispose(disposable)
+    val afterUnloading = psiManager.findFile(virtualFile)
+    UsefulTestCase.assertInstanceOf(afterUnloading!!.language, PlainTextLanguage::class.java)
+  }
+
+  private class TextToJavaSubstitutor : LanguageSubstitutor() {
+    override fun getLanguage(file: VirtualFile,
+                             project: Project): Language? {
+      return if (file.name.startsWith("dummy")) JavaLanguage.INSTANCE else null
+    }
+  }
+}