Avoid using task extensions at task execution time

Apparently the Gradle configuration cache does not permit accessing
task extensions at task execution time.  Instead, use task input
properties to store little bits of information that (1) influence a
task's own behavior and also (2) are needed in order to configure
*other* tasks' behaviors.

cast/java/test/data/build.gradle.kts

@@ -45,11 +45,15 @@ val downloadJLex by
     tasks.registering(VerifiedDownload::class) {
       src = URL("https://www.cs.princeton.edu/~appel/modern/java/JLex/current/Main.java")
       checksum = "fe0cff5db3e2f0f5d67a153cf6c783af"
-      val downloadedSourceDir by extra(layout.buildDirectory.dir(name))
-      dest = downloadedSourceDir.map { it.file("JLex/Main.java") }
+      val downloadedSourceDir = layout.buildDirectory.dir(name).map(Directory::toString)
+      inputs.property("downloadedSourceDir", downloadedSourceDir)
+      dest = layout.buildDirectory.dir(name).map { it.file("JLex/Main.java") }
     }
 
-sourceSets.test.get().java.srcDir(downloadJLex.map { it.extra["downloadedSourceDir"]!! })
+sourceSets.test
+    .get()
+    .java
+    .srcDir(downloadJLex.map { it.inputs.properties["downloadedSourceDir"]!! })
 
 ////////////////////////////////////////////////////////////////////////
 //

core/build.gradle.kts

@@ -172,7 +172,8 @@ val buildKawaTestJar by
 
 val downloadBcel by
     tasks.registering(VerifiedDownload::class) {
-      val basename by extra("bcel-5.2")
+      val basename = "bcel-5.2"
+      inputs.property("basename", basename)
       val archive = "${basename}.tar.gz"
       src = URL("https://archive.apache.org/dist/jakarta/bcel/binaries/$archive")
       dest = project.layout.buildDirectory.file(archive)
@@ -182,7 +183,7 @@ val downloadBcel by
 
 val extractBcel by
     tasks.registering {
-      val basename = downloadBcel.map { it.extra["basename"] as String }
+      val basename = downloadBcel.map { it.inputs.properties["basename"] as String }
       val jarFile = basename.flatMap { layout.buildDirectory.file("$name/${it}.jar") }
       inputs.files(downloadBcel.map { it.outputs.files })
       outputs.file(jarFile)