[IR] Allow inline modifier for functions returning MFVC without warning

Signed-off-by: Evgeniy.Zhelenskiy <Evgeniy.Zhelenskiy@jetbrains.com>

#KT-1179

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -17590,6 +17590,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/inline/superProperty.kt");
             }
 
+            @Test
+            @TestMetadata("valueClasses.kt")
+            public void testValueClasses() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inline/valueClasses.kt");
+            }
+
             @Test
             @TestMetadata("vararg.kt")
             public void testVararg() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java

@@ -17596,6 +17596,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/inline/superProperty.kt");
             }
 
+            @Test
+            @TestMetadata("valueClasses.kt")
+            public void testValueClasses() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inline/valueClasses.kt");
+            }
+
             @Test
             @TestMetadata("vararg.kt")
             public void testVararg() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java

@@ -17590,6 +17590,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/inline/superProperty.kt");
             }
 
+            @Test
+            @TestMetadata("valueClasses.kt")
+            public void testValueClasses() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inline/valueClasses.kt");
+            }
+
             @Test
             @TestMetadata("vararg.kt")
             public void testVararg() throws Exception {

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

@@ -10,16 +10,16 @@ import org.jetbrains.kotlin.builtins.StandardNames.BACKING_FIELD
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.EffectiveVisibility
 import org.jetbrains.kotlin.descriptors.Visibilities
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.FirElement
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.getModifier
 import org.jetbrains.kotlin.fir.analysis.checkers.isInlineOnly
 import org.jetbrains.kotlin.fir.analysis.checkers.unsubstitutedScope
 import org.jetbrains.kotlin.fir.analysis.collectors.AbstractDiagnosticCollectorVisitor
-import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
-import org.jetbrains.kotlin.diagnostics.reportOn
-import org.jetbrains.kotlin.fir.analysis.checkers.getModifier
 import org.jetbrains.kotlin.fir.containingClassLookupTag
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.*
@@ -27,18 +27,12 @@ import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.languageVersionSettings
 import org.jetbrains.kotlin.fir.references.FirSuperReference
 import org.jetbrains.kotlin.fir.references.toResolvedCallableSymbol
-import org.jetbrains.kotlin.fir.types.isBuiltinFunctionalType
-import org.jetbrains.kotlin.fir.types.isFunctionalType
-import org.jetbrains.kotlin.fir.types.isSuspendFunctionType
 import org.jetbrains.kotlin.fir.resolve.toSymbol
 import org.jetbrains.kotlin.fir.resolve.transformers.publishedApiEffectiveVisibility
 import org.jetbrains.kotlin.fir.scopes.getDirectOverriddenMembers
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.*
-import org.jetbrains.kotlin.fir.types.coneType
+import org.jetbrains.kotlin.fir.types.*
-import org.jetbrains.kotlin.fir.types.isMarkedNullable
-import org.jetbrains.kotlin.fir.types.isNullable
-import org.jetbrains.kotlin.fir.types.toSymbol
 import org.jetbrains.kotlin.fir.visitors.FirDefaultVisitor
 import org.jetbrains.kotlin.fir.visitors.FirVisitor
 import org.jetbrains.kotlin.lexer.KtTokens
@@ -446,6 +440,7 @@ abstract class FirInlineDeclarationChecker : FirFunctionChecker() {
             }
         if (hasInlinableParameters) return
         if (function.isInlineOnly()) return
+        if (function.returnTypeRef.needsMultiFieldValueClassFlattening(context.session)) return
 
         reporter.reportOn(function.source, FirErrors.NOTHING_TO_INLINE, context)
     }

compiler/frontend/src/org/jetbrains/kotlin/resolve/inline/InlineAnalyzerExtension.kt

@@ -23,12 +23,9 @@ import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
-import org.jetbrains.kotlin.resolve.AnalyzerExtensions
+import org.jetbrains.kotlin.resolve.*
-import org.jetbrains.kotlin.resolve.BindingContext
-import org.jetbrains.kotlin.resolve.BindingTrace
 import org.jetbrains.kotlin.resolve.calls.components.hasDefaultValue
 import org.jetbrains.kotlin.resolve.descriptorUtil.declaresOrInheritsDefaultValue
-import org.jetbrains.kotlin.resolve.isEffectivelyFinal
 
 class InlineAnalyzerExtension(
     private val reasonableInlineRules: Iterable<ReasonableInlineRule>,
@@ -183,6 +180,7 @@ class InlineAnalyzerExtension(
         ) return
 
         if (reasonableInlineRules.any { it.isInlineReasonable(functionDescriptor, function, trace.bindingContext) }) return
+        if (functionDescriptor.returnType?.needsMfvcFlattening() == true) return
 
         val reportOn = function.modifierList?.getModifier(KtTokens.INLINE_KEYWORD) ?: function
         trace.report(Errors.NOTHING_TO_INLINE.on(reportOn))

compiler/testData/diagnostics/tests/inline/valueClasses.kt

@@ -0,0 +1,12 @@
+// LANGUAGE: +ValueClasses
+// TARGET_BACKEND: JVM_IR
+// WITH_STDLIB
+// SKIP_TXT
+// FIR_IDENTICAL
+
+@JvmInline
+value class DPoint(val x: Double, val y: Double)
+
+inline fun f1() = DPoint(1.0, 2.0)
+<!NOTHING_TO_INLINE!>inline<!> fun f2() = 2U
+inline val p1 get() = DPoint(1.0, 2.0)

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -17596,6 +17596,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/inline/superProperty.kt");
             }
 
+            @Test
+            @TestMetadata("valueClasses.kt")
+            public void testValueClasses() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inline/valueClasses.kt");
+            }
+
             @Test
             @TestMetadata("vararg.kt")
             public void testVararg() throws Exception {