Show warning instead of error to eliminate breaking changes in 1.9.20
diff --git a/compiler/ir/serialization.js/src/org/jetbrains/kotlin/ir/backend/js/klib.kt b/compiler/ir/serialization.js/src/org/jetbrains/kotlin/ir/backend/js/klib.kt
index 2fe1e88..0d73f02 100644
--- a/compiler/ir/serialization.js/src/org/jetbrains/kotlin/ir/backend/js/klib.kt
+++ b/compiler/ir/serialization.js/src/org/jetbrains/kotlin/ir/backend/js/klib.kt
@@ -653,8 +653,8 @@
           |Note, that if the difference is only in letter cases, it also could lead to a clash of the compiled artifacts
     """.trimMargin()
 
-    irMessageLogger.report(IrMessageLogger.Severity.ERROR, message, null)
-    throw CompilationErrorException(message)
+    // It will be a warning until K2
+    irMessageLogger.report(IrMessageLogger.Severity.WARNING, message, null)
 }
 
 fun serializeModuleIntoKlib(
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kotlin2JsGradlePluginIT.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kotlin2JsGradlePluginIT.kt
index 2ca6f0d..5b991fb 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kotlin2JsGradlePluginIT.kt
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kotlin2JsGradlePluginIT.kt
@@ -363,8 +363,7 @@
     @GradleTest
     fun testPerFileProjectWithResultFilesClash(gradleVersion: GradleVersion) {
         project("kotlin-js-invalid-per-file-project", gradleVersion) {
-            buildAndFail("compileKotlinJs") {
-                assertTasksFailed(":compileKotlinJs")
+            build("compileKotlinJs") {
                 assertOutputContains("""
                    |There are clashes of file names and their package names in module 'kotlin-js-invalid-per-file-project'.
                    |  * Next files have package "com.example" and name "base":