FIR IDE: do not remove duplicated diagnostics

This hides the real problem why diagnostics are duplicated

idea/idea-fir/tests/org/jetbrains/kotlin/checkers/AbstractFirKotlinHighlightingPassTest.kt

@@ -6,10 +6,12 @@
 package org.jetbrains.kotlin.checkers
 
 import com.intellij.rt.execution.junit.FileComparisonFailure
+import org.jetbrains.kotlin.idea.highlighter.AbstractHighlightingTest
 import org.jetbrains.kotlin.idea.invalidateCaches
 import org.jetbrains.kotlin.idea.test.withCustomCompilerOptions
 import org.jetbrains.kotlin.idea.withPossiblyDisabledDuplicatedFirSourceElementsException
 import org.jetbrains.kotlin.psi.KtFile
+import org.jetbrains.kotlin.test.InTextDirectivesUtils
 import org.jetbrains.kotlin.test.uitls.IgnoreTests
 import org.jetbrains.kotlin.test.uitls.IgnoreTests.DIRECTIVES
 import org.jetbrains.kotlin.test.uitls.IgnoreTests.cleanUpIdenticalFirTestFile
@@ -45,14 +47,20 @@ abstract class AbstractFirKotlinHighlightingPassTest : AbstractKotlinHighlightin
         checkWeakWarnings: Boolean
     ): Long {
         val fileText = file.text
-        return withCustomCompilerOptions(fileText, project, module) {
-            try {
-                withPossiblyDisabledDuplicatedFirSourceElementsException(fileText) {
-                    myFixture.checkHighlighting(checkWarnings, checkInfos, checkWeakWarnings)
+        val isDuplicatedHighlightingExpected =
+            InTextDirectivesUtils.isDirectiveDefined(fileText, AbstractHighlightingTest.EXPECTED_DUPLICATED_HIGHLIGHTING_PREFIX)
+        var result: Long? = null
+        AbstractHighlightingTest.withExpectedDuplicatedHighlighting(isDuplicatedHighlightingExpected, /*isFirPlugin*/true) {
+            withCustomCompilerOptions(fileText, project, module) {
+                try {
+                    withPossiblyDisabledDuplicatedFirSourceElementsException(fileText) {
+                        result = myFixture.checkHighlighting(checkWarnings, checkInfos, checkWeakWarnings)
+                    }
+                } catch (e: FileComparisonFailure) {
+                    throw FileComparisonFailure(e.message, e.expected, e.actual, File(e.filePath).absolutePath)
                 }
-            } catch (e: FileComparisonFailure) {
-                throw FileComparisonFailure(e.message, e.expected, e.actual, File(e.filePath).absolutePath)
             }
         }
+        return result!!
     }
 }

idea/idea-frontend-fir/idea-fir-low-level-api/src/org/jetbrains/kotlin/idea/fir/low/level/api/file/structure/FileStructure.kt

@@ -64,12 +64,12 @@ internal class FileStructure(
     fun getAllDiagnosticsForFile(diagnosticCheckerFilter: DiagnosticCheckerFilter): Collection<FirPsiDiagnostic<*>> {
         val structureElements = getAllStructureElements()
 
-        return buildSet {
+        return buildList {
             collectDiagnosticsFromStructureElements(structureElements, diagnosticCheckerFilter)
         }
     }
 
-    private fun MutableSet<FirPsiDiagnostic<*>>.collectDiagnosticsFromStructureElements(
+    private fun MutableCollection<FirPsiDiagnostic<*>>.collectDiagnosticsFromStructureElements(
         structureElements: Collection<FileStructureElement>,
         diagnosticCheckerFilter: DiagnosticCheckerFilter
     ) {

idea/testData/checker/Constructors.fir.kt

@@ -1,4 +1,4 @@
-
+// EXPECTED_DUPLICATED_HIGHLIGHTING
 open class NoC
 class NoC1 : NoC()
 
@@ -18,7 +18,7 @@ class WithPC1(a : Int) {
 }
 
 
-class Foo() : WithPC0(), <error descr="Type expected"><error descr="[SYNTAX] Syntax error">this</error></error>() {
+class Foo() : WithPC0(), <error descr="Type expected"><error descr="[SYNTAX] Syntax error"><error descr="[SYNTAX] Syntax error">this</error></error></error>() {
 
 }
 

idea/testData/checker/Constructors.kt

@@ -1,4 +1,4 @@
-
+// EXPECTED_DUPLICATED_HIGHLIGHTING
 open class NoC
 class NoC1 : NoC()
 

idea/tests/org/jetbrains/kotlin/idea/highlighter/AbstractHighlightingTest.java

@@ -39,7 +39,7 @@ public abstract class AbstractHighlightingTest extends KotlinLightCodeInsightFix
 
         myFixture.configureByFile(fileName());
 
-        withExpectedDuplicatedHighlighting(expectedDuplicatedHighlighting, () -> {
+        withExpectedDuplicatedHighlighting(expectedDuplicatedHighlighting, isFirPlugin(), () -> {
             try {
                 checkHighlighting(fileText);
             }
@@ -54,7 +54,7 @@ public abstract class AbstractHighlightingTest extends KotlinLightCodeInsightFix
         });
     }
 
-    private void withExpectedDuplicatedHighlighting(boolean expectedDuplicatedHighlighting, Runnable runnable) {
+    public static void withExpectedDuplicatedHighlighting(boolean expectedDuplicatedHighlighting, boolean isFirPlugin, Runnable runnable) {
         if (!expectedDuplicatedHighlighting) {
             runnable.run();
             return;
@@ -63,7 +63,7 @@ public abstract class AbstractHighlightingTest extends KotlinLightCodeInsightFix
         try {
             ExpectedHighlightingData.expectedDuplicatedHighlighting(runnable);
         } catch (IllegalStateException e) {
-            if (isFirPlugin()) {
+            if (isFirPlugin) {
                 runnable.run();
             } else {
                 throw e;