[LL FIR] KT-50732 Add support for LL FIR-specific tests (.ll.kt)

- `.ll.kt` test data can be added in cases where LL FIR resolution
  legally diverges from K2 compiler results.
- Each `.ll.kt` test is prefixed with an `LL_FIR_DIVERGENCE` directive
  which must explain why the test may diverge from K2 compiler results.
  - `LLFirDivergenceCommentChecker` ensures that each `.ll.kt` file
    contains an `LL_FIR_DIVERGENCE` directive.
- `LLFirIdenticalChecker` results in an assertion error if the `.ll.kt`
  test and its base test are completely identical, including in their
  meta info (but ignoring `LL_FIR_DIVERGENCE`).
  - The checker additionally ensures that the base source file and the
    `.ll.kt` source file have identical Kotlin source code (ignoring
    meta info and `LL_FIR_DIVERGENCE`). This ensures that both tests
    test the exact same thing.
- `.ll.kt` files are ignored by select test generators, in addition to
  `.fir.kt` files.

compiler/tests-spec/tests/org/jetbrains/kotlin/spec/utils/TestsJsonMapGenerator.kt

@@ -15,6 +15,7 @@ import org.jetbrains.kotlin.spec.utils.models.LinkedSpecTest
 import org.jetbrains.kotlin.spec.utils.models.SpecPlace
 import org.jetbrains.kotlin.spec.utils.parsers.CommonParser
 import org.jetbrains.kotlin.spec.utils.parsers.LinkedSpecTestPatterns
+import org.jetbrains.kotlin.test.utils.isCustomTestData
 import java.io.File
 
 object TestsJsonMapGenerator {
@@ -68,7 +69,7 @@ object TestsJsonMapGenerator {
         TestArea.values().forEach { testArea ->
             File(testOrigin.getFilePath(testArea)).walkTopDown()
                 .forEach testFiles@{ file ->
-                    if (!file.isFile || file.extension != "kt" || file.name.endsWith(".fir.kt")) return@testFiles
+                    if (!file.isFile || file.extension != "kt" || file.isCustomTestData) return@testFiles
                     if (isImplementationTest && !LinkedSpecTestPatterns.testInfoPattern.matcher(file.readText()).find())
                         return@testFiles
 

compiler/tests-spec/tests/org/jetbrains/kotlin/spec/utils/tasks/GenerateSpecTests.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.spec.utils.tasks
 
+import org.jetbrains.kotlin.generators.generateTestGroupSuiteWithJUnit5
 import org.jetbrains.kotlin.generators.impl.generateTestGroupSuite
 import org.jetbrains.kotlin.spec.checkers.AbstractDiagnosticsTestSpec
 import org.jetbrains.kotlin.spec.codegen.AbstractBlackBoxCodegenTestSpec
@@ -14,8 +15,8 @@ import org.jetbrains.kotlin.spec.utils.GeneralConfiguration.SPEC_TEST_PATH
 import org.jetbrains.kotlin.spec.utils.GeneralConfiguration.TESTS_MAP_FILENAME
 import org.jetbrains.kotlin.spec.utils.SectionsJsonMapGenerator
 import org.jetbrains.kotlin.spec.utils.TestsJsonMapGenerator
-import org.jetbrains.kotlin.generators.generateTestGroupSuiteWithJUnit5
 import org.jetbrains.kotlin.test.runners.AbstractFirDiagnosticTestSpec
+import org.jetbrains.kotlin.test.utils.CUSTOM_TEST_DATA_EXTENSION_PATTERN
 import java.io.File
 import java.nio.file.Files
 
@@ -39,15 +40,13 @@ fun detectDirsWithTestsMapFileOnly(dirName: String, baseDir: String = "."): List
 }
 
 fun generateTests() {
-    val excludedFirTestdataPattern = "^(.+)\\.fir\\.kts?\$"
-
     generateTestGroupSuite {
         testGroup(SPEC_TEST_PATH, SPEC_TESTDATA_PATH) {
             testClass<AbstractDiagnosticsTestSpec> {
                 model(
                     "diagnostics",
                     excludeDirs = listOf("helpers") + detectDirsWithTestsMapFileOnly("diagnostics"),
-                    excludedPattern = excludedFirTestdataPattern
+                    excludedPattern = CUSTOM_TEST_DATA_EXTENSION_PATTERN
                 )
             }
 
@@ -70,7 +69,7 @@ fun generateTests() {
                 model(
                     "diagnostics",
                     excludeDirs = listOf("helpers") + detectDirsWithTestsMapFileOnly("diagnostics"),
-                    excludedPattern = excludedFirTestdataPattern
+                    excludedPattern = CUSTOM_TEST_DATA_EXTENSION_PATTERN
                 )
             }
         }