[KAPT4] Create basic infrastructure for KAPT4

plugins/kapt3/kapt3-cli/src/KaptCli.kt

@@ -114,7 +114,12 @@ private fun transformKaptToolArgs(args: List<String>, messageCollector: MessageC
     }
 
     if (!aptModePassed) {
-        transformed.addAll(0, kaptArg(KaptCliOption.APT_MODE_OPTION, "compile"))
+        val isK2 = "-Xuse-kapt4" in transformed && ("-Xuse-k2" in transformed ||
+                transformed.any { it.startsWith("-language-version=2") } ||
+                transformed.lastIndexOf("-language-version").takeIf { it >= 0 }
+                    ?.let { transformed.getOrNull(it + 1)?.startsWith('2') } == true)
+
+        transformed.addAll(0, kaptArg(KaptCliOption.APT_MODE_OPTION, if (isK2) "stubsAndApt" else "compile"))
     }
 
     if (!isTest && !isAtLeastJava9() && !areJavacComponentsAvailable() && !toolsJarPassed) {

plugins/kapt3/kapt3-cli/testData/integration/fallback/build.txt

@@ -47,8 +47,7 @@ output/sources/generated/Test.java
 Test.kt
 
 # output
-warning: kapt currently doesn't support language version 2.0+.
-Falling back to 1.9.
+warning: kapt currently doesn't support language version 2.0+. Falling back to 1.9.
 
 # java
 -cp output/classes:output/javaClasses:output/ap.jar:%KOTLIN_STDLIB%