Test the configuration cache after the extracted formatter is gone

With the formatter inside the plugin, the Spotless step signs the
extracted jars, and Spotless stores that signature in the
configuration cache entry: the jars are extracted, and checked for,
while the entry is stored. Gradle takes those checks for inputs, so a
build after the directory is deleted, or after the first extraction,
cannot reuse the entry and stores another; on a new machine or a new
plugin version that is one more configuration of every project.

spotlessApply_reuses_the_entry_after_the_extracted_formatter_is_deleted
fails on that, and is left out on Windows, which does not delete the
jars a daemon holds open.

Author: abashev

gradle-open-java-format/src/test/java/com/palantir/javaformat/gradle/ConfigurationCacheTest.java

@@ -27,6 +27,8 @@
 import org.gradle.testkit.runner.BuildTask;
 import org.gradle.testkit.runner.TaskOutcome;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledOnOs;
+import org.junit.jupiter.api.condition.OS;
 import org.junit.jupiter.api.io.TempDir;
 
 /**
@@ -96,6 +98,37 @@ void spotlessCheck_reports_the_violation_from_a_reused_entry() throws IOExceptio
         }
     }
 
+    @Test
+    @DisabledOnOs(
+            value = OS.WINDOWS,
+            disabledReason = "The daemon keeps the extracted jars open, and Windows does not delete an open file")
+    void spotlessApply_reuses_the_entry_after_the_extracted_formatter_is_deleted() throws IOException {
+        // The formatter inside the plugin, not the jars this build made: nothing in palantirJavaFormat.
+        var project = new GradleTestProject(projectDir)
+                .configurationCache(true)
+                .plugins("java", "dev.openjavaformat.java-format", "com.diffplug.spotless")
+                .withJavacInternalExports()
+                .buildGradle("println \"gradleUserHome=${gradle.gradleUserHomeDir}\"")
+                .writeFile(MAIN_JAVA, UNFORMATTED);
+        var stored = project.succeeds("spotlessApply");
+        assertThat(stored.getOutput()).contains(STORED);
+
+        // Storing the entry must not depend on the extracted jars, which a later build may find gone.
+        var gradleUserHome = stored.getOutput()
+                .lines()
+                .filter(line -> line.startsWith("gradleUserHome="))
+                .map(line -> Path.of(line.substring("gradleUserHome=".length())))
+                .findFirst()
+                .orElseThrow();
+        new GradleTestProject(gradleUserHome).delete("open-java-format-caches/" + BundledFormatter.hash());
+        project.writeFile(MAIN_JAVA, UNFORMATTED);
+
+        var reused = project.succeeds("spotlessApply");
+
+        assertThat(reused.getOutput()).contains(REUSED);
+        assertThat(project.readFile(MAIN_JAVA)).isEqualToNormalizingNewlines(FORMATTED);
+    }
+
     @Test
     void spotlessJava_is_up_to_date_until_the_formatter_jars_change() throws IOException, URISyntaxException {
         var jars = Files.readString(CLASSPATH_FILE).trim();