Fix XJC configuration to re-enable Eclipse IDE support

Our recent switch from the `org.unbroken-dome.xjc` plugin to the
`com.github.bjornvester.xjc` plugin resulted in errors when trying to
import Spring Framework projects into the Eclipse IDE.

This commit fixes those issues as follows.

- @wilkinsona revised the XJC configuration in `spring-oxm.gradle` to
  avoid the ConcurrentModificationException encountered when running
  `./gradlew eclipse`.

- I added a workaround in `ide.gradle` to manually remove lingering
  "main" classpath entries for sources generated by XJC.

Co-authored-by: Andy Wilkinson <andy.wilkinson@broadcom.com>

Closes gh-33264

gradle/ide.gradle

@@ -77,6 +77,19 @@ eclipse.classpath.file.whenMerged {
 	}
 }
 
+// Due to an apparent bug in Gradle, even though we exclude the "main" classpath
+// entries for sources generated by XJC in spring-oxm.gradle, the Gradle eclipse
+// plugin still includes them in the generated .classpath file. So, we have to
+// manually remove those lingering "main" entries.
+if (project.name == "spring-oxm") {
+	eclipse.classpath.file.whenMerged { classpath ->
+		classpath.entries.removeAll {
+			it.path =~ /build\/generated\/sources\/xjc\/.+/ &&
+			it.entryAttributes.get("gradle_scope") == "main"
+		}
+	}
+}
+
 // Include project specific settings
 task eclipseSettings(type: Copy) {
 	from rootProject.files(

spring-oxm/spring-oxm.gradle

@@ -20,7 +20,6 @@ dependencies {
 	testImplementation("org.codehaus.jettison:jettison") {
 		exclude group: "stax", module: "stax-api"
 	}
-	//testImplementation(files(genJaxb.classesDir).builtBy(genJaxb))
 	testImplementation("org.xmlunit:xmlunit-assertj")
 	testImplementation("org.xmlunit:xmlunit-matchers")
 	testRuntimeOnly("com.sun.xml.bind:jaxb-core")
@@ -28,14 +27,13 @@ dependencies {
 }
 
 tasks.named("xjc").configure { xjc ->
-	// XJC plugin only works against main sources
+	// XJC plugin only works against main sources, so we have to "move" them to test sources.
-	def javaSrcDirs = sourceSets.main.java.srcDirs
+	sourceSets.main.java.exclude {
-	javaSrcDirs.remove(file(xjc.outputJavaDir))
+		it.file.absolutePath.startsWith(outputJavaDir.get().asFile.absolutePath)
-	sourceSets.main.java.srcDirs = javaSrcDirs
+	}
-	def resourcesSrcDirs = sourceSets.main.resources.srcDirs
+	sourceSets.main.resources.exclude {
-	resourcesSrcDirs.remove(file(xjc.outputResourcesDir))
+		it.file.absolutePath.startsWith(outputResourcesDir.get().asFile.absolutePath)
-	sourceSets.main.resources.srcDirs = resourcesSrcDirs
+	}
-
 	sourceSets.test.java.srcDir(xjc.outputJavaDir)
 	sourceSets.test.resources.srcDir(xjc.outputResourcesDir)
 }