improvements after review

- make Gradle version compatibility clearer
- fix non-documentation tests
- revert explanations on applying the milestone and snapshot plugin on older gradle versions

Author: jnizet

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/asciidoc/getting-started.adoc

@@ -19,7 +19,16 @@ include::../gradle/getting-started/apply-plugin-release.gradle.kts[]
 ----
 endif::[]
 ifeval::["{version-type}" == "MILESTONE"]
-The plugin is published to the Spring milestones repository and can be applied using the `plugins` block:
+The plugin is published to the Spring milestones repository.
+
+For Gradle versions less than 4.10, you must apply the plugin imperatively:
+
+[source,groovy,indent=0,subs="verbatim,attributes"]
+----
+include::../gradle/getting-started/apply-plugin-milestone.gradle[]
+----
+
+For Gradle 4.10 and above, it can be applied using the `plugins` block:
 [source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
 .Groovy
 ----
@@ -32,7 +41,7 @@ include::../gradle/getting-started/apply-plugin-release.gradle[]
 include::../gradle/getting-started/apply-plugin-release.gradle.kts[]
 ----
 
-with the following lines in the `settings.gradle` file (or `settings.gradle.kts` in Kotlin):
+provided you add the following lines in the `settings.gradle` file (or `settings.gradle.kts` in Kotlin):
 
 [source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
 .Groovy
@@ -47,7 +56,16 @@ include::../gradle/getting-started/milestone-settings.gradle.kts[]
 ----
 endif::[]
 ifeval::["{version-type}" == "SNAPSHOT"]
-The plugin is published to the Spring snapshots repository and can be applied using the `plugins` block:
+The plugin is published to the Spring snapshots repository.
+
+For Gradle versions less than 4.10, you must apply the plugin imperatively:
+
+[source,groovy,indent=0,subs="verbatim,attributes"]
+----
+include::../gradle/getting-started/apply-plugin-snapshot.gradle[]
+----
+
+For Gradle 4.10 and above, it can be applied using the `plugins` block:
 [source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
 .Groovy
 ----
@@ -60,7 +78,7 @@ include::../gradle/getting-started/apply-plugin-release.gradle[]
 include::../gradle/getting-started/apply-plugin-release.gradle.kts[]
 ----
 
-with the following lines in the `settings.gradle` file (or `settings.gradle.kts` in Kotlin):
+provided you add the following lines in the `settings.gradle` file (or `settings.gradle.kts` in Kotlin):
 
 [source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
 .Groovy

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

@@ -37,7 +37,8 @@ Andy Wilkinson
 The Spring Boot Gradle Plugin provides Spring Boot support in https://gradle.org[Gradle],
 allowing 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 4.4 or later.
+Gradle plugin requires Gradle 4.4 or later. If you choose to use the newer Kotlin DSL,
+it requires Gradle 4.10 or later.
 
 In addition to this user guide, {api-documentation}[API documentation] is also available.
 
@@ -47,4 +48,4 @@ include::packaging.adoc[]
 include::publishing.adoc[]
 include::running.adoc[]
 include::integrating-with-actuator.adoc[]
-include::reacting.adoc[]
+include::reacting.adoc[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/getting-started/apply-plugin-milestone.gradle

@@ -0,0 +1,11 @@
+buildscript {
+    repositories {
+        maven { url 'https://repo.spring.io/libs-milestone' }
+    }
+
+    dependencies {
+        classpath 'org.springframework.boot:spring-boot-gradle-plugin:{version}'
+    }
+}
+
+apply plugin: 'org.springframework.boot'

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/getting-started/apply-plugin-snapshot.gradle

@@ -0,0 +1,11 @@
+buildscript {
+    repositories {
+        maven { url 'https://repo.spring.io/libs-snapshot' }
+    }
+
+    dependencies {
+        classpath 'org.springframework.boot:spring-boot-gradle-plugin:{version}'
+    }
+}
+
+apply plugin: 'org.springframework.boot'

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

@@ -25,6 +25,7 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.regex.Pattern;
+import java.util.stream.Collectors;
 
 import javax.xml.parsers.DocumentBuilderFactory;
 import javax.xml.xpath.XPath;
@@ -127,6 +128,11 @@ private List<File> pluginClasspath() {
 				new File(pathOfJarContaining(ArchiveEntry.class)));
 	}
 
+	private String pluginClasspathAsString() {
+		return pluginClasspath().stream().map(File::getAbsolutePath)
+				.collect(Collectors.joining(","));
+	}
+
 	private String pathOfJarContaining(Class<?> type) {
 		return type.getProtectionDomain().getCodeSource().getLocation().getPath();
 	}
@@ -174,6 +180,8 @@ public GradleRunner prepareRunner(String... arguments) throws IOException {
 		}
 		List<String> allArguments = new ArrayList<>();
 		allArguments.add("--stacktrace");
+		allArguments.add("-PpluginClasspath=" + pluginClasspathAsString());
+		allArguments.add("-PbootVersion=" + getBootVersion());
 		allArguments.addAll(Arrays.asList(arguments));
 		return gradleRunner.withArguments(allArguments);
 	}