[AA FIR] fix exception from vararg parameter with invalid type

It is true that for vararg parameter `arrayElementType` always have to
be not null, but it required resolution to TYPES phase. But in case of
the error type, the type reference is treated as resolved, so we are not
obligatory to resolve such reference to TYPES, because we already have
the resolved type.
So we can make the rule of KtFirValueParameterSymbol#returnType less
strict, and varargElementType will effectively do the same as
lazy resolve + arrayElementType

^KT-61422 Fixed

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/symbols/KtFirValueParameterSymbol.kt

@@ -24,10 +24,8 @@ import org.jetbrains.kotlin.fir.correspondingProperty
 import org.jetbrains.kotlin.fir.declarations.FirFunction
 import org.jetbrains.kotlin.fir.renderWithType
 import org.jetbrains.kotlin.fir.symbols.impl.FirValueParameterSymbol
-import org.jetbrains.kotlin.fir.types.arrayElementType
-import org.jetbrains.kotlin.fir.utils.exceptions.withFirEntry
+import org.jetbrains.kotlin.fir.types.varargElementType
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.utils.exceptions.errorWithAttachment
 
 internal class KtFirValueParameterSymbol(
     override val firSymbol: FirValueParameterSymbol,
@@ -50,13 +48,8 @@ internal class KtFirValueParameterSymbol(
 
     override val returnType by cached {
         val returnType = firSymbol.resolvedReturnType
-        return@cached if (firSymbol.isVararg) {
-            // There SHOULD always be an array element type (even if it is an error type, e.g., unresolved).
-            val arrayElementType = returnType.arrayElementType()
-                ?: errorWithAttachment("No array element type for vararg value parameter") {
-                    withFirEntry("fir", firSymbol.fir)
-                }
-            builder.typeBuilder.buildKtType(arrayElementType)
+        if (firSymbol.isVararg) {
+            builder.typeBuilder.buildKtType(returnType.varargElementType())
         } else {
             builder.typeBuilder.buildKtType(returnType)
         }

analysis/analysis-api-fir/tests-gen/org/jetbrains/kotlin/analysis/api/fir/test/cases/generated/cases/symbols/FirIdeNormalAnalysisSourceModuleSymbolByPsiTestGenerated.java

@@ -364,5 +364,17 @@ public class FirIdeNormalAnalysisSourceModuleSymbolByPsiTestGenerated extends Ab
         public void testParameterNotFunctionalType() throws Exception {
             runTest("analysis/analysis-api/testData/symbols/symbolByPsi/valueParameters/parameterNotFunctionalType.kt");
         }
+
+        @Test
+        @TestMetadata("vararg.kt")
+        public void testVararg() throws Exception {
+            runTest("analysis/analysis-api/testData/symbols/symbolByPsi/valueParameters/vararg.kt");
+        }
+
+        @Test
+        @TestMetadata("varargWithoutType.kt")
+        public void testVarargWithoutType() throws Exception {
+            runTest("analysis/analysis-api/testData/symbols/symbolByPsi/valueParameters/varargWithoutType.kt");
+        }
     }
 }