FIR: use more meaningful error messages

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/LookupTagUtils.kt

@@ -33,6 +33,12 @@ fun ConeClassLikeLookupTag.toSymbol(useSiteSession: FirSession): FirClassLikeSym
     }
 }
 
+@OptIn(LookupTagInternals::class)
+fun ConeClassLikeLookupTag.toSymbolOrError(useSiteSession: FirSession): FirClassLikeSymbol<*> =
+    toSymbol(useSiteSession)
+        ?: error("Class symbol with classId $classId was not found")
+
+
 fun ConeClassLikeLookupTag.toFirRegularClass(session: FirSession): FirRegularClass? =
     session.firSymbolProvider.getSymbolByLookupTag(this)?.fir as? FirRegularClass
 

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/tower/FirInvokeResolveTowerExtension.kt

@@ -262,8 +262,8 @@ private fun BodyResolveComponents.createExplicitReceiverForInvoke(
         is FirRegularClassSymbol -> buildResolvedQualifierForClass(symbol, sourceElement = null)
         is FirTypeAliasSymbol -> {
             val type = symbol.fir.expandedTypeRef.coneTypeUnsafe<ConeClassLikeType>().fullyExpandedType(session)
-            val expansionRegularClass = type.lookupTag.toSymbol(session)?.fir as? FirRegularClass
+            val expansionRegularClassSymbol = type.lookupTag.toSymbolOrError(session)
-            buildResolvedQualifierForClass(expansionRegularClass!!.symbol, sourceElement = symbol.fir.source)
+            buildResolvedQualifierForClass(expansionRegularClassSymbol, sourceElement = symbol.fir.source)
         }
         else -> throw AssertionError()
     }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirStatusResolveTransformer.kt

@@ -393,7 +393,9 @@ abstract class AbstractFirStatusResolveTransformer(
             }
             return
         }
-        require(file != null)
+        require(file != null) {
+            "Containing file was not found for\n${regularClass.render()}"
+        }
         val symbol = regularClass.symbol
         var declarationToStart: FirDeclaration? = null
         val designation = designationMapForLocalClasses[regularClass]?.let(::listOf)?.also {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/ConeTypeContext.kt

@@ -221,7 +221,7 @@ interface ConeTypeContext : TypeSystemContext, TypeSystemOptimizationContext, Ty
             is FirAnonymousObjectSymbol -> symbol.fir.typeParameters[index].symbol.toLookupTag()
             is FirRegularClassSymbol -> symbol.fir.typeParameters[index].symbol.toLookupTag()
             is FirTypeAliasSymbol -> symbol.fir.typeParameters[index].symbol.toLookupTag()
-            else -> error("?!:12")
+            else -> error("Unexpected FirClassLikeSymbol $symbol for ${this::class}, with classId ${(this as? ConeClassLikeLookupTag)?.classId}")
         }
     }
 

core/compiler.common/src/org/jetbrains/kotlin/types/AbstractTypeChecker.kt

@@ -69,7 +69,9 @@ abstract class AbstractTypeCheckerContext : TypeSystemContext {
 
 
     fun initialize() {
-        assert(!supertypesLocked)
+        assert(!supertypesLocked) {
+            "Supertypes were locked for ${this::class}"
+        }
         supertypesLocked = true
 
         if (supertypesDeque == null) {