Revert "Check JDK env vars once during configuration when not syncing"

This reverts commit 48b86bba

build.gradle.kts

@@ -122,19 +122,30 @@ extra["JDK_9"] = jdkPath("9")
 extra["JDK_10"] = jdkPath("10")
 extra["JDK_11"] = jdkPath("11")
 
-// allow opening the project without setting up all env variables (see KT-26413)
-if (!kotlinBuildProperties.isInIdeaSync) {
+gradle.taskGraph.beforeTask() {
     checkJDK()
 }
 
+var jdkChecked: Boolean = false
 fun checkJDK() {
-    val missingEnvVars = JdkMajorVersion.values()
-        .filter { it.isMandatory() && extra[it.name] == jdkNotFoundConst }
-        .mapTo(ArrayList()) { it.name }
-
-    if (missingEnvVars.isNotEmpty()) {
-        throw GradleException("Required environment variables are missing: ${missingEnvVars.joinToString()}")
+    if (jdkChecked) {
+        return
     }
+
+    val unpresentJdks = JdkMajorVersion.values()
+        .filter { it.isMandatory() }
+        .map { it.name }
+        .filter { extra[it] == jdkNotFoundConst }
+        .toList()
+
+    if (unpresentJdks.isNotEmpty()) {
+        throw GradleException("Please set environment variable" +
+                                      (if (unpresentJdks.size > 1) "s" else "") +
+                                      ": " + unpresentJdks.joinToString() +
+                                      " to point to corresponding JDK installation.")
+    }
+
+    jdkChecked = true
 }
 
 rootProject.apply {