[Analysis API] Support multi-module projects in compiler facility tests

analysis/analysis-api-impl-base/tests/org/jetbrains/kotlin/analysis/api/impl/base/test/cases/components/compilerFacility/AbstractCompilerFacilityTest.kt

@@ -69,9 +69,7 @@ abstract class AbstractCompilerFacilityTest : AbstractAnalysisApiBasedTest() {
     }
 
     override fun doTestByModuleStructure(moduleStructure: TestModuleStructure, testServices: TestServices) {
-        val mainModule = moduleStructure.modules.first { it.name == "main" }
-        val ktFiles = testServices.ktModuleProvider.getModuleFiles(mainModule).filterIsInstance<KtFile>()
-        val ktFile = ktFiles.singleOrNull() ?: ktFiles.first { it.name == "main.kt" }
+        val (mainModule, ktFile) = findTargetFile(moduleStructure, testServices)
 
         val irCollector = CollectingIrGenerationExtension()
 
@@ -119,6 +117,28 @@ abstract class AbstractCompilerFacilityTest : AbstractAnalysisApiBasedTest() {
         }
     }
 
+    private fun findTargetFile(moduleStructure: TestModuleStructure, testServices: TestServices): Pair<TestModule, KtFile> {
+        if (moduleStructure.modules.size == 1) {
+            val testModule = moduleStructure.modules.single()
+            val psiFiles = testServices.ktModuleProvider.getModuleFiles(testModule)
+            val ktFiles = psiFiles.filterIsInstance<KtFile>()
+            if (ktFiles.size == 1) {
+                // In simpler whole-file compilation tests, do not require the '<caret>'
+                return testModule to ktFiles.single()
+            }
+        }
+
+        for (testModule in moduleStructure.modules) {
+            for (psiFile in testServices.ktModuleProvider.getModuleFiles(testModule)) {
+                if (psiFile is KtFile && testServices.expressionMarkerProvider.getCaretPositionOrNull(psiFile) != null) {
+                    return testModule to psiFile
+                }
+            }
+        }
+
+        error("Cannot find the main test file")
+    }
+
     override fun configureTest(builder: TestConfigurationBuilder) {
         super.configureTest(builder)
         with(builder) {