Revert "Revert "Build: enable -Werror in stdlib/core/compiler/plugins modules""

This reverts commit 1300ec3e

build.gradle.kts

@@ -320,6 +320,25 @@ extra["compilerModulesForJps"] = listOf(
     ":compiler:compiler.version"
 )
 
+// TODO: fix remaining warnings and remove this property.
+extra["tasksWithWarnings"] = listOf(
+    ":kotlin-stdlib:compileTestKotlin",
+    ":kotlin-stdlib-jdk7:compileTestKotlin",
+    ":kotlin-stdlib-jdk8:compileTestKotlin",
+    ":compiler:cli:compileKotlin",
+    ":compiler:frontend:compileKotlin",
+    ":compiler:fir:tree:compileKotlin",
+    ":compiler:fir:resolve:compileKotlin",
+    ":compiler:fir:checkers:compileKotlin",
+    ":compiler:fir:java:compileKotlin",
+    ":kotlin-scripting-compiler:compileKotlin",
+    ":plugins:uast-kotlin:compileKotlin",
+    ":plugins:uast-kotlin:compileTestKotlin",
+    ":plugins:uast-kotlin-idea:compileKotlin"
+)
+
+val tasksWithWarnings: List<String> by extra
+
 val coreLibProjects = listOfNotNull(
     ":kotlin-stdlib",
     ":kotlin-stdlib-common",
@@ -452,6 +471,21 @@ allprojects {
         }
     }
 
+    if (!kotlinBuildProperties.isInJpsBuildIdeaSync && !kotlinBuildProperties.useFir) {
+        // For compiler and stdlib, allWarningsAsErrors is configured in the corresponding "root" projects
+        // (compiler/build.gradle.kts and libraries/commonConfiguration.gradle).
+        val projectsWithWarningsAsErrors = listOf("core", "plugins").map { File(it).absoluteFile }
+        if (projectsWithWarningsAsErrors.any(projectDir::startsWith)) {
+            tasks.withType<org.jetbrains.kotlin.gradle.dsl.KotlinJvmCompile> {
+                if (path !in tasksWithWarnings) {
+                    kotlinOptions {
+                        allWarningsAsErrors = true
+                    }
+                }
+            }
+        }
+    }
+
     tasks.withType(VerificationTask::class.java as Class<Task>) {
         (this as VerificationTask).ignoreFailures = ignoreTestFailures
     }