Fix Eclipse WTP facet version

Add `WarConventions` to fix the facet version used by Eclipse WTP

buildSrc/src/main/java/org/springframework/boot/build/ConventionsPlugin.java

@@ -47,6 +47,7 @@ public class ConventionsPlugin implements Plugin<Project> {
 		new MavenPublishingConventions().apply(project);
 		new AsciidoctorConventions().apply(project);
 		new KotlinConventions().apply(project);
+		new WarConventions().apply(project);
 	}
 
 }

buildSrc/src/main/java/org/springframework/boot/build/WarConventions.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.build;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.gradle.api.JavaVersion;
+import org.gradle.api.Project;
+import org.gradle.api.internal.IConventionAware;
+import org.gradle.api.plugins.JavaPluginExtension;
+import org.gradle.plugins.ide.eclipse.EclipseWtpPlugin;
+import org.gradle.plugins.ide.eclipse.model.EclipseModel;
+import org.gradle.plugins.ide.eclipse.model.Facet;
+
+/**
+ * Conventions that are applied in the presence of the {WarPlugin}. When the plugin is
+ * applied:
+ * <ul>
+ * <li>Update Eclipse WTP Plugin facets to use Servlet 5.0</li>
+ * </ul>
+ *
+ * @author Phillip Webb
+ */
+public class WarConventions {
+
+	void apply(Project project) {
+		project.getPlugins().withType(EclipseWtpPlugin.class, (wtp) -> {
+			project.getTasks().getByName(EclipseWtpPlugin.ECLIPSE_WTP_FACET_TASK_NAME).doFirst((task) -> {
+				EclipseModel eclipseModel = project.getExtensions().getByType(EclipseModel.class);
+				((IConventionAware) eclipseModel.getWtp().getFacet()).getConventionMapping()
+					.map("facets", () -> getFacets(project));
+			});
+		});
+	}
+
+	private List<Facet> getFacets(Project project) {
+		JavaVersion javaVersion = project.getExtensions().getByType(JavaPluginExtension.class).getSourceCompatibility();
+		List<Facet> facets = new ArrayList<>();
+		facets.add(new Facet(Facet.FacetType.fixed, "jst.web", null));
+		facets.add(new Facet(Facet.FacetType.installed, "jst.web", "5.0"));
+		facets.add(new Facet(Facet.FacetType.installed, "jst.java", javaVersion.toString()));
+		return facets;
+	}
+
+}