FIR: Weaken requirements for all symbols to have correct FIR

Currently, some cases like library type parameters are not supported properly

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

@@ -10,7 +10,6 @@ import org.jetbrains.kotlin.fir.declarations.expandedConeType
 import org.jetbrains.kotlin.fir.render
 import org.jetbrains.kotlin.fir.symbols.*
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeAliasSymbol
-import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.types.impl.ConeAbbreviatedTypeImpl
 import org.jetbrains.kotlin.fir.types.impl.ConeClassTypeImpl
@@ -42,11 +41,10 @@ fun ConeAbbreviatedType.directExpansionType(useSiteSession: FirSession): ConeCla
 fun ConeClassifierLookupTag.toSymbol(useSiteSession: FirSession): ConeClassifierSymbol? =
     when (this) {
         is ConeClassLikeLookupTag -> toSymbol(useSiteSession)
-        is FirTypeParameterSymbol -> this.symbol
+        is ConeTypeParameterSymbol -> this
         else -> error("sealed")
     }
 
-
 fun ConeClassifierSymbol.constructType(typeArguments: Array<ConeKotlinTypeProjection>, isNullable: Boolean): ConeLookupTagBasedType {
     return when (this) {
         is ConeTypeParameterSymbol -> {
@@ -127,4 +125,4 @@ fun <T : ConeKotlinType> T.withArguments(arguments: Array<ConeKotlinTypeProjecti
         //is ConeFunctionTypeImpl -> ConeFunctionTypeImpl(receiverType, parameterTypes, returnType, lookupTag, nullability.isNullable) as T
         else -> error("Not supported: $this: ${this.render()}")
     }
-}
+}

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

@@ -8,9 +8,11 @@ package org.jetbrains.kotlin.fir.resolve
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.FirRegularClass
 import org.jetbrains.kotlin.fir.declarations.FirTypeParameter
+import org.jetbrains.kotlin.fir.resolve.transformers.firSafeNullable
 import org.jetbrains.kotlin.fir.resolve.transformers.firUnsafe
 import org.jetbrains.kotlin.fir.scopes.FirScope
 import org.jetbrains.kotlin.fir.scopes.impl.FirCompositeScope
+import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.types.impl.ConeClassTypeImpl
 import org.jetbrains.kotlin.fir.types.impl.ConeTypeParameterTypeImpl
@@ -21,11 +23,15 @@ fun ConeKotlinType.scope(useSiteSession: FirSession): FirScope? {
         is ConeClassErrorType -> null
         is ConeAbbreviatedType -> directExpansionType(useSiteSession)?.scope(useSiteSession)
         is ConeClassLikeType -> {
-            val fir = this.lookupTag.toSymbol(useSiteSession)?.firUnsafe<FirRegularClass>() ?: return null
+            // For ConeClassLikeType they might be a type alias instead of a regular class
+            // TODO: support that case and switch back to `firUnsafe` instead of `firSafeNullable`
+            val fir = this.lookupTag.toSymbol(useSiteSession)?.firSafeNullable<FirRegularClass>() ?: return null
             fir.buildUseSiteScope(useSiteSession)
         }
         is ConeTypeParameterType -> {
-            val fir = this.lookupTag.toSymbol(useSiteSession)?.firUnsafe<FirTypeParameter>() ?: return null
+            // TODO: support LibraryTypeParameterSymbol or get rid of it
+            val toSymbol = this.lookupTag.toSymbol(useSiteSession)?.takeIf { it is FirBasedSymbol<*> } ?: return null
+            val fir = toSymbol.firUnsafe<FirTypeParameter>()
             FirCompositeScope(fir.bounds.mapNotNullTo(mutableListOf()) { it.coneTypeUnsafe().scope(useSiteSession) })
         }
         is ConeFlexibleType -> lowerBound.scope(useSiteSession)
@@ -47,4 +53,4 @@ fun FirRegularClass.defaultType(): ConeClassTypeImpl {
         }.toTypedArray(),
         isNullable = false
     )
-}
+}

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

@@ -544,6 +544,11 @@ inline fun <reified T : FirElement> ConeSymbol.firUnsafe(): T {
     return fir
 }
 
+inline fun <reified T : FirElement> ConeSymbol.firSafeNullable(): T? {
+    if (this !is FirBasedSymbol<*>) return null
+    return fir as? T
+}
+
 
 interface ReturnTypeCalculator {
     fun tryCalculateReturnType(declaration: FirTypedDeclaration): FirResolvedTypeRef