Modernize Antora Build (#3309)

This PR is an attempt to apply some modernization related to Antora gradle build.
It is related to spring-projects/spring-framework#32864
Notice that the @springio/antora-extensions is not used because it uses springio/antora-extensions/set-algolia-env-extension which is currently not compatible with projectreactor.

Author: pderop

.gitignore

@@ -18,4 +18,6 @@ exportToHtml
 .rulesets
 .gradletasknamecache
 *.iml
-.idea
+.idea
+node_modules/
+.full-build

build.gradle

@@ -140,13 +140,6 @@ ext {
 
 	// Antora
 	antoraPluginVersion = '1.0.0'
-	antoraVersion = '3.2.0-alpha.4'
-	antoraAtlasExtensionVersion = '1.0.0-alpha.1'
-	antoraPdfExtensionVersion = '1.0.0-alpha.7'
-	antoraCollectorExtensionVersion = '1.0.0-alpha.3'
-	asciiDocTabVersion = '1.0.0-beta.6'
-	springIoAntoraExtensionsVersion = '1.8.2'
-	springIoAsciidoctorExtensionsVersion = '1.0.0-alpha.9'
 
 	javadocLinks = ["https://docs.oracle.com/javase/8/docs/api/",
 					// Use Reactive Streams 1.0.3 version for javadoc generation

docs/package.json

@@ -0,0 +1,11 @@
+{
+	"dependencies": {
+		"antora": "3.2.0-alpha.4",
+		"@antora/atlas-extension": "1.0.0-alpha.2",
+		"@antora/collector-extension": "1.0.0-alpha.3",
+		"@antora/pdf-extension": "1.0.0-alpha.7",
+		"@asciidoctor/tabs": "1.0.0-beta.6",
+		"@springio/antora-extensions": "1.11.1",
+		"@springio/asciidoctor-extensions": "1.0.0-alpha.10"
+	}
+}

gradle/antora-docs.gradle

@@ -26,9 +26,7 @@ def isCommandAvailable(String command) {
 }
 
 antora {
-	version = "$antoraVersion"
-	playbook = findProperty('antora.playbook') ?: "antora-playbook.yml"
-	options = ['--clean', '--stacktrace']
+	options = [clean: true, fetch: !project.gradle.startParameter.offline, stacktrace: true]
 
 	def version = project.version
 	def forcePdf = project.hasProperty('forcePdf')
@@ -47,15 +45,6 @@ antora {
 			'ALGOLIA_APP_ID'    : '82SNR5M8HE',
 			'ALGOLIA_INDEX_NAME': 'projectreactor'
 	]
-
-	dependencies = [
-			'@antora/atlas-extension'         : "$antoraAtlasExtensionVersion",
-			'@antora/pdf-extension'           : "$antoraPdfExtensionVersion",
-			'@antora/collector-extension'     : "$antoraCollectorExtensionVersion",
-			'@asciidoctor/tabs'               : "$asciiDocTabVersion",
-			'@springio/antora-extensions'     : "$springIoAntoraExtensionsVersion",
-			'@springio/asciidoctor-extensions': "$springIoAsciidoctorExtensionsVersion"
-	]
 }
 
 jar {