Add release type attribute for Antora documentation generation

Fixes gh-41993

Author: scottfrederick

buildSrc/src/main/java/org/springframework/boot/build/antora/AntoraAsciidocAttributes.java

@@ -77,7 +77,7 @@ public Map<String, String> get() {
 		Map<String, String> attributes = new LinkedHashMap<>();
 		addGitHubAttributes(attributes);
 		addVersionAttributes(attributes);
-		addUrlArtifactRepository(attributes);
+		addArtifactAttributes(attributes);
 		addUrlJava(attributes);
 		addUrlLibraryLinkAttributes(attributes);
 		addPropertyAttributes(attributes);
@@ -139,8 +139,9 @@ private void addDependencyVersion(Map<String, String> attributes, String name, S
 		attributes.put("version-" + name, version);
 	}
 
-	private void addUrlArtifactRepository(Map<String, String> attributes) {
+	private void addArtifactAttributes(Map<String, String> attributes) {
 		attributes.put("url-artifact-repository", this.artifactRelease.getDownloadRepo());
+		attributes.put("artifact-release-type", this.artifactRelease.getType());
 	}
 
 	private void addUrlJava(Map<String, String> attributes) {

buildSrc/src/test/java/org/springframework/boot/build/antora/AntoraAsciidocAttributesTests.java

@@ -112,6 +112,27 @@ void urlArtifactRepositoryWhenSnapshot() {
 		assertThat(attributes.get()).containsEntry("url-artifact-repository", "https://repo.spring.io/snapshot");
 	}
 
+	@Test
+	void artifactReleaseTypeWhenRelease() {
+		AntoraAsciidocAttributes attributes = new AntoraAsciidocAttributes("1.2.3", true, null,
+				mockDependencyVersions(), null);
+		assertThat(attributes.get()).containsEntry("artifact-release-type", "release");
+	}
+
+	@Test
+	void artifactReleaseTypeWhenMilestone() {
+		AntoraAsciidocAttributes attributes = new AntoraAsciidocAttributes("1.2.3-M1", true, null,
+				mockDependencyVersions(), null);
+		assertThat(attributes.get()).containsEntry("artifact-release-type", "milestone");
+	}
+
+	@Test
+	void artifactReleaseTypeWhenSnapshot() {
+		AntoraAsciidocAttributes attributes = new AntoraAsciidocAttributes("1.2.3-SNAPSHOT", true, null,
+				mockDependencyVersions(), null);
+		assertThat(attributes.get()).containsEntry("artifact-release-type", "snapshot");
+	}
+
 	@Test
 	void urlLinksFromLibrary() {
 		Map<String, Function<LibraryVersion, String>> links = new LinkedHashMap<>();