Drop support for Gradle 5.6.x

Closes gh-24225

spring-boot-project/spring-boot-docs/src/docs/asciidoc/build-tool-plugins.adoc

@@ -24,7 +24,6 @@ Please refer to the plugin's documentation to learn more:
 == Spring Boot Gradle Plugin
 The Spring Boot Gradle Plugin provides Spring Boot support in Gradle, letting you package executable jar or war archives, run Spring Boot applications, and use the dependency management provided by `spring-boot-dependencies`.
 It requires Gradle 6 (6.3 or later).
-Gradle 5.6.x is also supported but this support is deprecated and will be removed in a future release.
 Please refer to the plugin's documentation to learn more:
 
 * Reference ({spring-boot-gradle-plugin-docs}[HTML] and {spring-boot-gradle-plugin-pdfdocs}[PDF])

spring-boot-project/spring-boot-docs/src/docs/asciidoc/getting-started.adoc

@@ -118,7 +118,6 @@ More details on getting started with Spring Boot and Maven can be found in the {
 [[getting-started-gradle-installation]]
 ==== Gradle Installation
 Spring Boot is compatible with Gradle 6 (6.3 or later).
-Gradle 5.6.x is also supported but this support is deprecated and will be removed in a future release.
 If you do not already have Gradle installed, you can follow the instructions at https://gradle.org.
 
 Spring Boot dependencies can be declared by using the `org.springframework.boot` `group`.

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/asciidoc/index.adoc

@@ -42,7 +42,6 @@ Andy Wilkinson, Scott Frederick
 The Spring Boot Gradle Plugin provides Spring Boot support in https://gradle.org[Gradle].
 It allows you to package executable jar or war archives, run Spring Boot applications, and use the dependency management provided by `spring-boot-dependencies`.
 Spring Boot's Gradle plugin requires Gradle 6 (6.3 or later).
-Gradle 5.6 is also supported but this support is deprecated and will be removed in a future release.
 Gradle's {gradle-userguide}/configuration_cache.html[configuration cache] is supported when using Gradle 6.7 or later.
 
 In addition to this user guide, {api-documentation}[API documentation] is also available.

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/SpringBootPlugin.java

@@ -95,10 +95,8 @@ public class SpringBootPlugin implements Plugin<Project> {
 
 	private void verifyGradleVersion() {
 		GradleVersion currentVersion = GradleVersion.current();
-		if (currentVersion.compareTo(GradleVersion.version("5.6")) < 0
-				|| (currentVersion.getBaseVersion().compareTo(GradleVersion.version("6.0")) >= 0
-						&& currentVersion.compareTo(GradleVersion.version("6.3")) < 0)) {
-			throw new GradleException("Spring Boot plugin requires Gradle 5 (5.6.x only) or Gradle 6 (6.3 or later). "
+		if (currentVersion.compareTo(GradleVersion.version("6.3")) < 0) {
+			throw new GradleException("Spring Boot plugin requires Gradle 6 (6.3 or later). "
 					+ "The current version is " + currentVersion);
 		}
 	}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/junit/GradleCompatibilityExtension.java

@@ -21,7 +21,6 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Stream;
 
-import org.gradle.api.JavaVersion;
 import org.gradle.util.GradleVersion;
 import org.junit.jupiter.api.TestTemplate;
 import org.junit.jupiter.api.extension.Extension;
@@ -43,19 +42,8 @@ import org.springframework.util.StringUtils;
  */
 final class GradleCompatibilityExtension implements TestTemplateInvocationContextProvider {
 
-	private static final List<String> GRADLE_VERSIONS;
-
-	static {
-		JavaVersion javaVersion = JavaVersion.current();
-		if (javaVersion.isCompatibleWith(JavaVersion.VERSION_14)
-				|| javaVersion.isCompatibleWith(JavaVersion.VERSION_13)) {
-			GRADLE_VERSIONS = Arrays.asList("6.3", "6.4.1", "6.5.1", "6.6.1", "6.7.1", "current", "7.0-milestone-3");
-		}
-		else {
-			GRADLE_VERSIONS = Arrays.asList("5.6.4", "6.3", "6.4.1", "6.5.1", "6.6.1", "6.7.1", "current",
-					"7.0-milestone-3");
-		}
-	}
+	private static final List<String> GRADLE_VERSIONS = Arrays.asList("6.3", "6.4.1", "6.5.1", "6.6.1", "6.7.1",
+			"current", "7.0-milestone-3");
 
 	@Override
 	public Stream<TestTemplateInvocationContext> provideTestTemplateInvocationContexts(ExtensionContext context) {

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/SpringBootPluginIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -16,9 +16,6 @@
 
 package org.springframework.boot.gradle.plugin;
 
-import java.io.File;
-import java.io.IOException;
-
 import org.gradle.testkit.runner.BuildResult;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.condition.DisabledForJreRange;
@@ -40,34 +37,12 @@ class SpringBootPluginIntegrationTests {
 
 	final GradleBuild gradleBuild = new GradleBuild();
 
-	@DisabledForJreRange(min = JRE.JAVA_14)
-	@Test
-	void failFastWithVersionOfGradle5LowerThanRequired() {
-		BuildResult result = this.gradleBuild.gradleVersion("5.5.1").buildAndFail();
-		assertThat(result.getOutput())
-				.contains("Spring Boot plugin requires Gradle 5 (5.6.x only) or Gradle 6 (6.3 or later). "
-						+ "The current version is Gradle 5.5.1");
-	}
-
 	@DisabledForJreRange(min = JRE.JAVA_14)
 	@Test
 	void failFastWithVersionOfGradle6LowerThanRequired() {
 		BuildResult result = this.gradleBuild.gradleVersion("6.2.2").buildAndFail();
 		assertThat(result.getOutput())
-				.contains("Spring Boot plugin requires Gradle 5 (5.6.x only) or Gradle 6 (6.3 or later). "
-						+ "The current version is Gradle 6.2.2");
-	}
-
-	@DisabledForJreRange(min = JRE.JAVA_13)
-	@Test
-	void succeedWithVersionOfGradle5HigherThanRequired() {
-		this.gradleBuild.gradleVersion("5.6.1").build();
-	}
-
-	@DisabledForJreRange(min = JRE.JAVA_13)
-	@Test
-	void succeedWithVersionOfGradle5MatchingWhatIsRequired() {
-		this.gradleBuild.gradleVersion("5.6").build();
+				.contains("Spring Boot plugin requires Gradle 6 (6.3 or later). The current version is Gradle 6.2.2");
 	}
 
 	@Test
@@ -75,10 +50,4 @@ class SpringBootPluginIntegrationTests {
 		this.gradleBuild.gradleVersion("6.3").build();
 	}
 
-	private void createMinimalMainSource() throws IOException {
-		File examplePackage = new File(this.gradleBuild.getProjectDir(), "src/main/java/com/example");
-		examplePackage.mkdirs();
-		new File(examplePackage, "Application.java").createNewFile();
-	}
-
 }