[FIR] Warn about inline enum entries

^KT-42096 Fixed
^KTLC-361

Author: lunakoly

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

@@ -34,6 +34,7 @@ import org.jetbrains.kotlin.fir.symbols.impl.FirScriptSymbol
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.lexer.KtTokens.DATA_KEYWORD
+import org.jetbrains.kotlin.lexer.KtTokens.INLINE_KEYWORD
 import org.jetbrains.kotlin.resolve.*
 
 object FirModifierChecker : FirBasicDeclarationChecker(MppCheckerKind.Common) {
@@ -115,12 +116,18 @@ object FirModifierChecker : FirBasicDeclarationChecker(MppCheckerKind.Common) {
             }
             val set = map[modifierToken] ?: emptySet()
             val checkResult = if (factory == FirErrors.WRONG_MODIFIER_TARGET) {
-                actualTargets.none { it in set } ||
-                        (modifierToken == DATA_KEYWORD
-                                && actualTargets.contains(KotlinTarget.STANDALONE_OBJECT)
-                                && !LanguageFeature.DataObjects.isEnabled())
+                actualTargets.none { it in set }
+                        || (modifierToken == DATA_KEYWORD
+                        && actualTargets.contains(KotlinTarget.STANDALONE_OBJECT)
+                        && !LanguageFeature.DataObjects.isEnabled())
+                        || (modifierToken == INLINE_KEYWORD
+                        && actualTargets.contains(KotlinTarget.ENUM_ENTRY)
+                        && LanguageFeature.ForbidInlineEnumEntries.isEnabled())
             } else {
                 actualTargets.any { it in set }
+                        || (modifierToken == INLINE_KEYWORD
+                        && actualTargets.contains(KotlinTarget.ENUM_ENTRY)
+                        && !LanguageFeature.ForbidInlineEnumEntries.isEnabled())
             }
             if (checkResult) {
                 reporter.reportOn(

compiler/testData/diagnostics/tests/inlineEnumEntries.fir.kt

@@ -0,0 +1,16 @@
+// LATEST_LV_DIFFERENCE
+// RUN_PIPELINE_TILL: BACKEND
+// ISSUE: KT-42096
+
+enum class E {
+    <!DEPRECATED_MODIFIER_FOR_TARGET!>inline<!> E1 {
+        override fun invoke() = 123
+    };
+    abstract fun invoke(): Int
+}
+
+fun main() {
+    E.E1.invoke()
+}
+
+/* GENERATED_FIR_TAGS: enumDeclaration, enumEntry, functionDeclaration */

compiler/testData/diagnostics/tests/inlineEnumEntries.kt

@@ -1,4 +1,4 @@
-// FIR_IDENTICAL
+// LATEST_LV_DIFFERENCE
 // RUN_PIPELINE_TILL: BACKEND
 // ISSUE: KT-42096
 

compiler/testData/diagnostics/tests/inlineEnumEntries.latestLV.kt

@@ -0,0 +1,16 @@
+// LATEST_LV_DIFFERENCE
+// RUN_PIPELINE_TILL: BACKEND
+// ISSUE: KT-42096
+
+enum class E {
+    <!WRONG_MODIFIER_TARGET!>inline<!> E1 {
+        override fun invoke() = 123
+    };
+    abstract fun invoke(): Int
+}
+
+fun main() {
+    E.E1.invoke()
+}
+
+/* GENERATED_FIR_TAGS: enumDeclaration, enumEntry, functionDeclaration */

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -450,6 +450,7 @@ enum class LanguageFeature(
     AllowReifiedTypeInCatchClause(KOTLIN_2_4, issue = "KT-54363"),
     ForbidGetSetValueWithTooManyParameters(KOTLIN_2_4, issue = "KT-77131"),
     ForbidReturnInExpressionBodyWithoutExplicitTypeEdgeCases(KOTLIN_2_4, enabledInProgressiveMode = true, "KTLC-288"),
+    ForbidInlineEnumEntries(KOTLIN_2_4, enabledInProgressiveMode = true, "KTLC-361"),
     CheckOptInOnPureEnumEntries(KOTLIN_2_4, enabledInProgressiveMode = true, "KTLC-359"),
     ForbidExposingPackagePrivateInInternal(KOTLIN_2_4, enabledInProgressiveMode = true, "KTLC-271"),