FIR IDE: do not fail on building anonymous function symbol

idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/inspections/declarations/HLRedundantUnitReturnTypeInspection.kt

@@ -35,7 +35,7 @@ internal class HLRedundantUnitReturnTypeInspection :
 
     override val inputProvider = inputProvider<KtNamedFunction, CallableReturnTypeUpdaterApplicator.Type> { function ->
         when {
-            function.getFunctionSymbol().annotatedType.type.isUnit -> CallableReturnTypeUpdaterApplicator.Type.UNIT
+            function.getFunctionLikeSymbol().annotatedType.type.isUnit -> CallableReturnTypeUpdaterApplicator.Type.UNIT
             else -> null
         }
     }

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/symbols/KtSymbolProvider.kt

@@ -15,7 +15,7 @@ import org.jetbrains.kotlin.psi.*
 abstract class KtSymbolProvider : KtAnalysisSessionComponent() {
     open fun getSymbol(psi: KtDeclaration): KtSymbol = when (psi) {
         is KtParameter -> getParameterSymbol(psi)
-        is KtNamedFunction -> getFunctionSymbol(psi)
+        is KtNamedFunction -> getFunctionLikeSymbol(psi)
         is KtConstructor<*> -> getConstructorSymbol(psi)
         is KtTypeParameter -> getTypeParameterSymbol(psi)
         is KtTypeAlias -> getTypeAliasSymbol(psi)
@@ -32,7 +32,7 @@ abstract class KtSymbolProvider : KtAnalysisSessionComponent() {
 
     abstract fun getParameterSymbol(psi: KtParameter): KtValueParameterSymbol
     abstract fun getFileSymbol(psi: KtFile): KtFileSymbol
-    abstract fun getFunctionSymbol(psi: KtNamedFunction): KtFunctionSymbol
+    abstract fun getFunctionLikeSymbol(psi: KtNamedFunction): KtFunctionLikeSymbol
     abstract fun getConstructorSymbol(psi: KtConstructor<*>): KtConstructorSymbol
     abstract fun getTypeParameterSymbol(psi: KtTypeParameter): KtTypeParameterSymbol
     abstract fun getTypeAliasSymbol(psi: KtTypeAlias): KtTypeAliasSymbol
@@ -57,8 +57,14 @@ interface KtSymbolProviderMixIn : KtAnalysisSessionMixIn {
     fun KtParameter.getParameterSymbol(): KtValueParameterSymbol =
         analysisSession.symbolProvider.getParameterSymbol(this)
 
-    fun KtNamedFunction.getFunctionSymbol(): KtFunctionSymbol =
-        analysisSession.symbolProvider.getFunctionSymbol(this)
+    /**
+     * Creates [KtFunctionLikeSymbol] by [KtNamedFunction]
+     *
+     * If [KtNamedFunction.getName] is `null` then returns [KtAnonymousFunctionSymbol]
+     * Otherwise, returns [KtFunctionSymbol]
+     */
+    fun KtNamedFunction.getFunctionLikeSymbol(): KtFunctionLikeSymbol =
+        analysisSession.symbolProvider.getFunctionLikeSymbol(this)
 
     fun KtConstructor<*>.getConstructorSymbol(): KtConstructorSymbol =
         analysisSession.symbolProvider.getConstructorSymbol(this)

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/symbols/KtFirSymbolProvider.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.idea.frontend.api.fir.symbols
 
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.renderWithType
 import org.jetbrains.kotlin.fir.resolve.providers.FirSymbolProvider
 import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
 import org.jetbrains.kotlin.idea.fir.low.level.api.api.FirModuleResolveState
@@ -43,9 +44,13 @@ internal class KtFirSymbolProvider(
         firSymbolBuilder.buildFileSymbol(psi.getFirFile(resolveState))
     }
 
-    override fun getFunctionSymbol(psi: KtNamedFunction): KtFunctionSymbol = withValidityAssertion {
-        psi.withFirDeclarationOfType<FirSimpleFunction, KtFunctionSymbol>(resolveState) {
-            firSymbolBuilder.functionLikeBuilder.buildFunctionSymbol(it)
+    override fun getFunctionLikeSymbol(psi: KtNamedFunction): KtFunctionLikeSymbol = withValidityAssertion {
+        psi.withFirDeclarationOfType<FirFunction<*>, KtFunctionLikeSymbol>(resolveState) { fir ->
+            when (fir) {
+                is FirSimpleFunction -> firSymbolBuilder.functionLikeBuilder.buildFunctionSymbol(fir)
+                is FirAnonymousFunction -> firSymbolBuilder.functionLikeBuilder.buildAnonymousFunctionSymbol(fir)
+                else -> error("Unexpected ${fir.renderWithType()}")
+            }
         }
     }