[FIR] Report UNSUPPORTED_FEATURE for expect/actual members if MPP is disabled

Always enable MultiPlatformProjects for K2MetadataCompilerArguments

 ^KT-57243 Fixed

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

@@ -868,8 +868,12 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
             if (internalArguments.isNotEmpty()) {
                 configureLanguageFeaturesFromInternalArgs(collector)
             }
+
+            configureExtraLanguageFeatures(this)
         }
 
+    protected open fun configureExtraLanguageFeatures(map: HashMap<LanguageFeature, LanguageFeature.State>) {}
+
     private fun HashMap<LanguageFeature, LanguageFeature.State>.configureLanguageFeaturesFromInternalArgs(collector: MessageCollector) {
         val featuresThatForcePreReleaseBinaries = mutableListOf<LanguageFeature>()
         val disabledFeaturesFromUnsupportedVersions = mutableListOf<LanguageFeature>()

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2MetadataCompilerArguments.kt

@@ -16,6 +16,8 @@
 
 package org.jetbrains.kotlin.cli.common.arguments
 
+import org.jetbrains.kotlin.config.LanguageFeature
+
 class K2MetadataCompilerArguments : CommonCompilerArguments() {
     companion object {
         @JvmStatic private val serialVersionUID = 0L
@@ -80,4 +82,8 @@ class K2MetadataCompilerArguments : CommonCompilerArguments() {
         }
 
     override fun copyOf(): Freezable = copyK2MetadataCompilerArguments(this, K2MetadataCompilerArguments())
+
+    override fun configureExtraLanguageFeatures(map: HashMap<LanguageFeature, LanguageFeature.State>) {
+        map[LanguageFeature.MultiPlatformProjects] = LanguageFeature.State.ENABLED
+    }
 }

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/RedundantModalityModifierChecker.kt

@@ -1,3 +1,5 @@
+// LANGUAGE: +MultiPlatformProjects
+
 object O {
     fun foo() {}
 }

compiler/fir/analysis-tests/testData/resolve/multifile/simpleStarImport.kt

@@ -1,3 +1,5 @@
+// LANGUAGE: +MultiPlatformProjects
+
 // FILE: B.kt
 
 package b.d

compiler/fir/analysis-tests/testData/resolve/problems/expectConstructor.kt

@@ -1,3 +1,5 @@
+// LANGUAGE: +MultiPlatformProjects
+
 open class Base(v: String)
 
 expect class Derived(v: String) : Base

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirExpectActualDeclarationChecker.kt

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.SourceElementPositioningStrategies
 import org.jetbrains.kotlin.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
@@ -35,8 +36,19 @@ import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstanceOrNull
 @Suppress("DuplicatedCode")
 object FirExpectActualDeclarationChecker : FirBasicDeclarationChecker() {
     override fun check(declaration: FirDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
-        if (!context.session.languageVersionSettings.supportsFeature(LanguageFeature.MultiPlatformProjects)) return
         if (declaration !is FirMemberDeclaration) return
+        if (!context.session.languageVersionSettings.supportsFeature(LanguageFeature.MultiPlatformProjects)) {
+            if ((declaration.isExpect || declaration.isActual) && context.containingDeclarations.lastOrNull() is FirFile) {
+                reporter.reportOn(
+                    declaration.source,
+                    FirErrors.UNSUPPORTED_FEATURE,
+                    LanguageFeature.MultiPlatformProjects to context.session.languageVersionSettings,
+                    context,
+                    positioningStrategy = SourceElementPositioningStrategies.EXPECT_ACTUAL_MODIFIER
+                )
+            }
+            return
+        }
         if (declaration.isExpect) {
             checkExpectDeclarationModifiers(declaration, context, reporter)
         }

compiler/testData/cli/metadata/hmppModules.args

@@ -5,7 +5,6 @@ $TESTDATA_DIR$/../jvm/hmpp/src/c.kt
 $TEMP_DIR$
 -language-version
 2.0
--XXLanguage\:+MultiPlatformProjects
 -Xfragments=a,b,c
 -Xfragment-sources=a\:$TESTDATA_DIR$/../jvm/hmpp/src/a.kt
 -Xfragment-sources=b\:$TESTDATA_DIR$/../jvm/hmpp/src/b.kt

compiler/testData/cli/metadata/hmppModules.out

@@ -1,12 +1,3 @@
-warning: ATTENTION!
-This build uses unsafe internal compiler arguments:
-
--XXLanguage:+MultiPlatformProjects
-
-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!
-
 warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
 error: HMPP module structure should not be passed during metadata compilation. Please remove `-Xfragments` and related flags
 COMPILATION_ERROR

compiler/testData/cli/metadata/inheritorOfExpectSealedClassWithFir.args

@@ -3,6 +3,11 @@ $TESTDATA_DIR$/inheritorOfExpectSealedClass/common-2.kt
 $TESTDATA_DIR$/inheritorOfExpectSealedClass/common-3.kt
 -d
 $TEMP_DIR$
--Xcommon-sources=$TESTDATA_DIR$/inheritorOfExpectSealedClass/common-1.kt,$TESTDATA_DIR$/inheritorOfExpectSealedClass/common-2.kt
 -language-version
 2.0
+-Xfragments=a,b,c
+-Xfragment-sources=a\:$TESTDATA_DIR$/inheritorOfExpectSealedClass/common-1.kt
+-Xfragment-sources=b\:$TESTDATA_DIR$/inheritorOfExpectSealedClass/common-2.kt
+-Xfragment-sources=c\:$TESTDATA_DIR$/inheritorOfExpectSealedClass/common-3.kt
+-Xfragment-refines=b\:a
+-Xfragment-refines=c\:b

compiler/testData/cli/metadata/inheritorOfExpectSealedClassWithFir.out

@@ -1,2 +1,3 @@
 warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
-OK
+error: HMPP module structure should not be passed during metadata compilation. Please remove `-Xfragments` and related flags
+COMPILATION_ERROR

compiler/testData/diagnostics/tests/sourceCompatibility/noMultiplatformProjects.fir.kt

@@ -1,7 +0,0 @@
-expect fun foo1()
-expect val bar1 = <!EXPECTED_PROPERTY_INITIALIZER!>42<!>
-expect class Baz1
-
-actual fun foo2() = 42
-<!MUST_BE_INITIALIZED!>actual val bar2: Int<!>
-actual interface Baz2

compiler/testData/diagnostics/tests/sourceCompatibility/noMultiplatformProjects.kt

@@ -1,6 +1,11 @@
+// FIR_IDENTICAL
 <!UNSUPPORTED_FEATURE!>expect<!> fun foo1()
 <!UNSUPPORTED_FEATURE!>expect<!> val bar1 = <!EXPECTED_PROPERTY_INITIALIZER!>42<!>
-<!UNSUPPORTED_FEATURE!>expect<!> class Baz1
+<!UNSUPPORTED_FEATURE!>expect<!> class Baz1 {
+    fun foo()
+
+    class Baz12
+}
 
 <!UNSUPPORTED_FEATURE!>actual<!> fun foo2() = 42
 <!MUST_BE_INITIALIZED!><!UNSUPPORTED_FEATURE!>actual<!> val bar2: Int<!>