Reintroduce compile dependency on apiguardian-api in Maven POMs

Resolves junit-team#1105.

build.gradle

@@ -6,12 +6,10 @@ buildscript {
 		// mavenLocal()
 		maven { url 'https://plugins.gradle.org/m2/' }
 		maven { url 'https://oss.sonatype.org/content/repositories/snapshots' }
-		maven { url 'http://repo.spring.io/plugins-release' }
 	}
 	dependencies {
 		classpath('com.diffplug.spotless:spotless-plugin-gradle:3.6.0')
 		classpath('com.github.ben-manes:gradle-versions-plugin:0.17.0')
-		classpath('io.spring.gradle:propdeps-plugin:0.0.10.RELEASE')
 		classpath('org.ajoberstar:gradle-git-publish:0.3.2')
 		classpath('org.ajoberstar:gradle-git:1.7.2')
 		classpath('org.junit.platform:junit-platform-gradle-plugin:1.0.1')
@@ -117,9 +115,7 @@ allprojects { subproj ->
 	}
 
 	dependencies {
-		// The following dependency is necessary to avoid compiler warnings about
-		// not being able to find the @API annotation when compiling test sources.
-		testCompileOnly("org.apiguardian:apiguardian-api:${apiGuardianVersion}")
+		api("org.apiguardian:apiguardian-api:${apiGuardianVersion}")
 	}
 
 	tasks.withType(Test) { task ->
@@ -254,10 +250,6 @@ allprojects { subproj ->
 subprojects { subproj ->
 	if (subproj.name in mavenizedProjects) {
 		apply plugin: 'maven'
-		apply plugin: 'propdeps'
-		apply plugin: 'propdeps-maven'
-		apply plugin: 'propdeps-idea'
-		apply plugin: 'propdeps-eclipse'
 		apply plugin: 'signing'
 
 		if (subproj.name in platformProjects) {
@@ -269,13 +261,6 @@ subprojects { subproj ->
 			subproj.version = vintageVersion
 		}
 
-		dependencies {
-			// The 'optional' configuration is provided by the propdeps-plugin and allows
-			// us to declare dependencies that get flagged as optional in the generated
-			// Maven POMs.
-			optional("org.apiguardian:apiguardian-api:${apiGuardianVersion}")
-		}
-
 		javadoc {
 			options.memberLevel = JavadocMemberLevel.PROTECTED
 			options.author = true

documentation/documentation.gradle

@@ -95,6 +95,7 @@ asciidoctor {
 				'vintage-version': project.property('vintageVersion'),
 				'junit4-version': project.property('junit4Version'),
 				'apiguardian-version': project.property('apiGuardianVersion'),
+				'ota4j-version': project.property('ota4jVersion'),
 				'release-branch': project.property('releaseBranch'),
 				'revnumber' : project.version,
 				'mainDir': project.sourceSets.main.java.srcDirs[0],

documentation/src/docs/asciidoc/release-notes/release-notes-5.1.0-M2.adoc

@@ -9,6 +9,22 @@ For a complete list of all _closed_ issues and pull requests for this release, c
 link:{junit5-repo}+/milestone/18?closed=1+[5.1 M2] milestone page in the JUnit repository
 on GitHub.
 
+[[release-notes-5.1.0-M2-overall-improvements]]
+=== Overall Improvements
+
+* In 5.0.1, all artifacts were changed to have an _optional_ instead of a mandatory
+  dependency on the _@API Guardian_ JAR in their published Maven POMs. However, although
+  the Java compiler should ignore missing annotation types, a lot of users have reported
+  that compiling tests without having the _@API Guardian_ JAR on the classpath results in
+  warnings emitted by `javac` that look like this:
++
+----
+warning: unknown enum constant Status.STABLE
+reason: class file for org.apiguardian.api.API$Status not found
+----
++
+To avoid confusion, the JUnit team has decided to make the dependency to the
+_@API Guardian_ JAR _mandatory_ again.
 
 [[release-notes-5.1.0-M2-junit-platform]]
 === JUnit Platform

documentation/src/docs/asciidoc/user-guide/overview.adoc

@@ -122,16 +122,23 @@ Snapshot artifacts are deployed to Sonatype's {snapshot-repo}[snapshots reposito
     JUnit Vintage test engine implementation that allows to run vintage JUnit tests, i.e. tests
     written in the JUnit 3 or JUnit 4 style, on the new JUnit Platform.
 
-[[dependency-metadata-optional-dependencies]]
-==== Optional Dependencies
+[[dependency-metadata-dependencies]]
+==== Dependencies
 
-All of the above artifacts have an `optional` dependency in their published Maven POMs on
+All of the above artifacts have a dependency in their published Maven POMs on
 the following _@API Guardian_ JAR.
 
 * *Group ID*: `org.apiguardian`
 * *Artifact ID*: `apiguardian-api`
 * *Version*: `{apiguardian-version}`
 
+In addition, most of the above artifacts have a direct or transitive dependency to the
+following _OpenTest4J_ JAR.
+
+* *Group ID*: `org.opentest4j`
+* *Artifact ID*: `opentest4j`
+* *Version*: `{ota4j-version}`
+
 [[dependency-diagram]]
 === Dependency Diagram
 
@@ -168,6 +175,19 @@ package org.opentest4j {
     [opentest4j]
 }
 
+package org.apiguardian {
+    [apiguardian-api] as apiguardian
+    note bottom of apiguardian #white
+        All artifacts except
+        opentest4j and junit:junit
+        have a dependency on this
+        artifact. The edges have
+        been omitted from this
+        diagram for the sake of
+        readability.
+    endnote
+}
+
 jupiter_api ..> opentest4j
 jupiter_api ..> commons