Reinstate checkstyle for reference docs code snippets

This commit also ensures that checks are performed before the
application is rendered to get early feedback on errors.

framework-docs/framework-docs.gradle

@@ -18,10 +18,6 @@ dependencies {
 	implementation("org.assertj:assertj-core")
 }
 
-checkstyle {
-	sourceSets = []
-}
-
 jar {
 	enabled = false
 }
@@ -128,6 +124,8 @@ asciidoctor {
 	}
 }
 
+asciidoctor.mustRunAfter "check"
+
 /**
  * Generate the Spring Framework Reference documentation from "src/docs/asciidoc"
  * in "build/docs/ref-docs/pdf".

framework-docs/src/main/java/org/springframework/docs/core/aot/hints/testing/SampleReflectionRuntimeHintsTests.java

@@ -39,9 +39,8 @@ class SampleReflectionRuntimeHintsTests {
 	void shouldRegisterReflectionHints() {
 		RuntimeHints runtimeHints = new RuntimeHints();
 		// Call a RuntimeHintsRegistrar that contributes hints like:
-		runtimeHints.reflection().registerType(SpringVersion.class, typeHint -> {
-			typeHint.withMethod("getVersion", List.of(), ExecutableMode.INVOKE);
-		});
+		runtimeHints.reflection().registerType(SpringVersion.class, typeHint ->
+				typeHint.withMethod("getVersion", List.of(), ExecutableMode.INVOKE));
 
 		// Invoke the relevant piece of code we want to test within a recording lambda
 		RuntimeHintsInvocations invocations = RuntimeHintsRecorder.record(() -> {

src/checkstyle/checkstyle-suppressions.xml

@@ -12,6 +12,9 @@
 	<!-- JMH benchmarks -->
 	<suppress files="[\\/]src[\\/]jmh[\\/]java[\\/]org[\\/]springframework[\\/]" checks="JavadocVariable|JavadocStyle|InnerTypeLast"/>
 
+	<!-- Framework docs -->
+	<suppress files="org[\\/]springframework[\\/]docs[\\/].+" checks="IllegalImport" id="bannedJUnitJupiterImports" />
+
 	<!-- spring-aop -->
 	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]aopalliance[\\/]" checks="IllegalImport" id="bannedImports" message="javax"/>