[FIR] Allow, but also warn, KMutableProperty with captured types

^KT-63589 Fixed

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -2662,6 +2662,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.MUTABLE_PROPERTY_WITH_CAPTURED_TYPE) { firDiagnostic ->
+        MutablePropertyWithCapturedTypeImpl(
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.NOTHING_TO_OVERRIDE) { firDiagnostic ->
         NothingToOverrideImpl(
             firSymbolBuilder.callableBuilder.buildCallableSymbol(firDiagnostic.a),

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -1885,6 +1885,10 @@ sealed interface KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = UnsupportedClassLiteralsWithEmptyLhs::class
     }
 
+    interface MutablePropertyWithCapturedType : KtFirDiagnostic<PsiElement> {
+        override val diagnosticClass get() = MutablePropertyWithCapturedType::class
+    }
+
     interface NothingToOverride : KtFirDiagnostic<KtModifierListOwner> {
         override val diagnosticClass get() = NothingToOverride::class
         val declaration: KtCallableSymbol

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -2266,6 +2266,11 @@ internal class UnsupportedClassLiteralsWithEmptyLhsImpl(
     token: KtLifetimeToken,
 ) : KtAbstractFirDiagnostic<KtElement>(firDiagnostic, token), KtFirDiagnostic.UnsupportedClassLiteralsWithEmptyLhs
 
+internal class MutablePropertyWithCapturedTypeImpl(
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<PsiElement>(firDiagnostic, token), KtFirDiagnostic.MutablePropertyWithCapturedType
+
 internal class NothingToOverrideImpl(
     override val declaration: KtCallableSymbol,
     firDiagnostic: KtPsiDiagnostic,