Improved parsing of internal compiler arguments with boolean state in

case when the argument is listed twice in the list of command line
arguments. The last value will be used.
#KT-27181 Fixed

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/parseCommandLineArguments.kt

@@ -135,7 +135,15 @@ private fun <A : CommonToolArguments> parsePreprocessedCommandLineArguments(args
             if (parser == null) {
                 errors.unknownExtraFlags += arg
             } else {
-                internalArguments.add(parser.parseInternalArgument(arg, errors) ?: continue)
+                val newInternalArgument = parser.parseInternalArgument(arg, errors) ?: continue
+                val argumentWillBeOverridden = when (newInternalArgument) {
+                    is ManualLanguageFeatureSetting -> internalArguments.firstOrNull { (it is ManualLanguageFeatureSetting) && (it.languageFeature == newInternalArgument.languageFeature) }
+                    else -> null
+                }
+                if (argumentWillBeOverridden != null) {
+                    internalArguments.remove(argumentWillBeOverridden)
+                }
+                internalArguments.add(newInternalArgument)
             }
 
             continue

compiler/testData/cli/jvm/internalArgOverrideLanguageFeature.args

@@ -0,0 +1,5 @@
+$TESTDATA_DIR$/inlineClass.kt
+-d
+$TEMP_DIR$
+-XXLanguage:-InlineClasses
+-XXLanguage:+InlineClasses

compiler/testData/cli/jvm/internalArgOverrideLanguageFeature.out

@@ -0,0 +1,10 @@
+warning: ATTENTION!
+This build uses unsafe internal compiler arguments:
+
+-XXLanguage;+InlineClasses
+
+This mode is not recommended for production use,
+as no stability/compatibility guarantees are given on
+compiler or generated code. Use it at your own risk!
+
+OK

compiler/testData/cli/jvm/internalArgOverrideOffLanguageFeature.args

@@ -0,0 +1,5 @@
+$TESTDATA_DIR$/inlineClass.kt
+-d
+$TEMP_DIR$
+-XXLanguage:+InlineClasses
+-XXLanguage:-InlineClasses

compiler/testData/cli/jvm/internalArgOverrideOffLanguageFeature.out

@@ -0,0 +1,13 @@
+warning: ATTENTION!
+This build uses unsafe internal compiler arguments:
+
+-XXLanguage;-InlineClasses
+
+This mode is not recommended for production use,
+as no stability/compatibility guarantees are given on
+compiler or generated code. Use it at your own risk!
+
+compiler/testData/cli/jvm/inlineClass.kt:1:1: error: the feature "inline classes" is disabled
+inline class Foo(val x: Int)
+^
+COMPILATION_ERROR

compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -296,6 +296,16 @@ public class CliTestGenerated extends AbstractCliTest {
             runTest("compiler/testData/cli/jvm/internalArgNoWarningForEnablingBugfix.args");
         }
 
+        @TestMetadata("internalArgOverrideLanguageFeature.args")
+        public void testInternalArgOverrideLanguageFeature() throws Exception {
+            runTest("compiler/testData/cli/jvm/internalArgOverrideLanguageFeature.args");
+        }
+
+        @TestMetadata("internalArgOverrideOffLanguageFeature.args")
+        public void testInternalArgOverrideOffLanguageFeature() throws Exception {
+            runTest("compiler/testData/cli/jvm/internalArgOverrideOffLanguageFeature.args");
+        }
+
         @TestMetadata("internalArgUnrecognizedFeature.args")
         public void testInternalArgUnrecognizedFeature() throws Exception {
             runTest("compiler/testData/cli/jvm/internalArgUnrecognizedFeature.args");