Remove spring-boot.version property from spring-boot-dependencies

The version of Spring Boot should not be modifiable by a property,
only being using a different version of spring-boot-dependencies or
spring-boot-starter-parent.

Fixes gh-23174

buildSrc/src/main/java/org/springframework/boot/build/bom/BomExtension.java

@@ -169,15 +169,18 @@ public class BomExtension {
 
 	private void addLibrary(Library library) {
 		this.libraries.add(library);
-		this.properties.put(library.getVersionProperty(), library.getVersion());
+		String versionProperty = library.getVersionProperty();
+		if (versionProperty != null) {
+			this.properties.put(versionProperty, library.getVersion());
+		}
 		for (Group group : library.getGroups()) {
 			for (Module module : group.getModules()) {
-				putArtifactVersionProperty(group.getId(), module.getName(), library.getVersionProperty());
+				putArtifactVersionProperty(group.getId(), module.getName(), versionProperty);
 				this.dependencyHandler.getConstraints().add(JavaPlatformPlugin.API_CONFIGURATION_NAME,
 						createDependencyNotation(group.getId(), module.getName(), library.getVersion()));
 			}
 			for (String bomImport : group.getBoms()) {
-				putArtifactVersionProperty(group.getId(), bomImport, library.getVersionProperty());
+				putArtifactVersionProperty(group.getId(), bomImport, versionProperty);
 				String bomDependency = createDependencyNotation(group.getId(), bomImport, library.getVersion());
 				this.dependencyHandler.add(JavaPlatformPlugin.API_CONFIGURATION_NAME,
 						this.dependencyHandler.platform(bomDependency));

buildSrc/src/main/java/org/springframework/boot/build/bom/BomPlugin.java

@@ -168,7 +168,10 @@ public class BomPlugin implements Plugin<Project> {
 						Node plugin = new Node(plugins, "plugin");
 						plugin.appendNode("groupId", group.getId());
 						plugin.appendNode("artifactId", pluginName);
-						plugin.appendNode("version", "${" + library.getVersionProperty() + "}");
+						String versionProperty = library.getVersionProperty();
+						String value = (versionProperty != null) ? "${" + versionProperty + "}"
+								: library.getVersion().toString();
+						plugin.appendNode("version", value);
 					}
 				}
 			}

buildSrc/src/main/java/org/springframework/boot/build/bom/Library.java

@@ -55,7 +55,8 @@ public class Library {
 		this.name = name;
 		this.version = version;
 		this.groups = groups;
-		this.versionProperty = name.toLowerCase(Locale.ENGLISH).replace(' ', '-') + ".version";
+		this.versionProperty = "Spring Boot".equals(name) ? null
+				: name.toLowerCase(Locale.ENGLISH).replace(' ', '-') + ".version";
 		this.prohibitedVersions = prohibitedVersions;
 	}
 

buildSrc/src/main/java/org/springframework/boot/build/constraints/ExtractVersionConstraints.java

@@ -103,7 +103,10 @@ public class ExtractVersionConstraints extends DefaultTask {
 		Object bom = getProject().project(projectPath).getExtensions().getByName("bom");
 		BomExtension bomExtension = (BomExtension) bom;
 		for (Library lib : bomExtension.getLibraries()) {
-			this.versionProperties.add(new VersionProperty(lib.getName(), lib.getVersionProperty()));
+			String versionProperty = lib.getVersionProperty();
+			if (versionProperty != null) {
+				this.versionProperties.add(new VersionProperty(lib.getName(), versionProperty));
+			}
 		}
 	}
 

buildSrc/src/test/java/org/springframework/boot/build/bom/BomPluginIntegrationTests.java

@@ -16,11 +16,9 @@
 package org.springframework.boot.build.bom;
 
 import java.io.File;
-import java.io.FileReader;
 import java.io.FileWriter;
 import java.io.IOException;
 import java.io.PrintWriter;
-import java.io.Reader;
 import java.util.function.Consumer;
 
 import org.gradle.testkit.runner.BuildResult;
@@ -31,7 +29,6 @@ import org.junit.jupiter.api.io.TempDir;
 
 import org.springframework.boot.build.DeployedPlugin;
 import org.springframework.boot.build.assertj.NodeAssert;
-import org.springframework.util.FileCopyUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -172,6 +169,33 @@ public class BomPluginIntegrationTests {
 		});
 	}
 
+	@Test
+	void libraryNamedSpringBootHasNoVersionProperty() throws IOException {
+		try (PrintWriter out = new PrintWriter(new FileWriter(this.buildFile))) {
+			out.println("plugins {");
+			out.println("    id 'org.springframework.boot.bom'");
+			out.println("}");
+			out.println("bom {");
+			out.println("    library('Spring Boot', '1.2.3') {");
+			out.println("        group('org.springframework.boot') {");
+			out.println("            modules = [");
+			out.println("                'spring-boot'");
+			out.println("            ]");
+			out.println("        }");
+			out.println("    }");
+			out.println("}");
+		}
+		generatePom((pom) -> {
+			assertThat(pom).textAtPath("//properties/spring-boot.version").isEmpty();
+			NodeAssert dependency = pom.nodeAtPath("//dependencyManagement/dependencies/dependency[1]");
+			assertThat(dependency).textAtPath("groupId").isEqualTo("org.springframework.boot");
+			assertThat(dependency).textAtPath("artifactId").isEqualTo("spring-boot");
+			assertThat(dependency).textAtPath("version").isEqualTo("1.2.3");
+			assertThat(dependency).textAtPath("scope").isNullOrEmpty();
+			assertThat(dependency).textAtPath("type").isNullOrEmpty();
+		});
+	}
+
 	private BuildResult runGradle(String... args) {
 		return GradleRunner.create().withDebug(true).withProjectDir(this.projectDir).withArguments(args)
 				.withPluginClasspath().build();
@@ -180,12 +204,6 @@ public class BomPluginIntegrationTests {
 	private void generatePom(Consumer<NodeAssert> consumer) {
 		runGradle(DeployedPlugin.GENERATE_POM_TASK_NAME, "-s");
 		File generatedPomXml = new File(this.projectDir, "build/publications/maven/pom-default.xml");
-		try (Reader reader = new FileReader(generatedPomXml)) {
-			System.out.println(FileCopyUtils.copyToString(reader));
-		}
-		catch (IOException ex) {
-
-		}
 		assertThat(generatedPomXml).isFile();
 		consumer.accept(new NodeAssert(generatedPomXml));
 	}