FIR: handle double-imported qualifiers properly

compiler/fir/tree/src/org/jetbrains/kotlin/fir/scopes/FirScope.kt

@@ -38,7 +38,7 @@ abstract class FirScope {
     open val scopeOwnerLookupNames: List<String> get() = emptyList()
 }
 
-fun FirScope.getSingleClassifier(name: Name): FirClassifierSymbol<*>? = mutableListOf<FirClassifierSymbol<*>>().apply {
+fun FirScope.getSingleClassifier(name: Name): FirClassifierSymbol<*>? = mutableSetOf<FirClassifierSymbol<*>>().apply {
     processClassifiersByName(name, this::add)
 }.singleOrNull()
 

compiler/testData/diagnostics/tests/imports/DoubleImports.kt

@@ -3,7 +3,9 @@
 
 package star
 
-class SomeClass
+class SomeClass {
+    class Nested
+}
 
 fun foo() {}
 
@@ -32,6 +34,8 @@ import explicit.gau
 
 fun useSomeClass(): SomeClass = SomeClass()
 
+fun useNested(): SomeClass.Nested = SomeClass.Nested()
+
 fun useAnotherClass(): AnotherClass = AnotherClass()
 
 fun test() {

compiler/testData/diagnostics/tests/imports/DoubleImports.txt

@@ -2,6 +2,7 @@ package
 
 public fun test(): kotlin.Unit
 public fun useAnotherClass(): explicit.AnotherClass
+public fun useNested(): star.SomeClass.Nested
 public fun useSomeClass(): star.SomeClass
 
 package explicit {
@@ -25,5 +26,12 @@ package star {
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
         public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+        public final class Nested {
+            public constructor Nested()
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
     }
 }