[build] Use Spotless plugin to enforce/update copyright headers (reac…

…tor#2729)

This commit introduces the Spotless plugin, which is capable of only
applying checks to files that have changed compared to a given branch
(by default in this PR, 3.3.x).

For now, only java files are considered, excluding JDK stubs.

This allows to enforce license header with up-to-date end year only when
a file get touched (no need for a big bang update of the end year in
all files comes new year).

The year variable in the template is compatible with IntelliJ's own
template format (velocity), although IntelliJ doesn't typically include
the comment characters like in the added template file.
The template includes 2 blank lines at the end so that one blank line
remains after the license header once spotless is applied.

The ratchet (apply spotless only to files that changed between current
commit and the specified branch) is adapted depending on local build,
CI build without any specific parameter and CI build explicitly intended
for spotless (thanks to -PspotlessFrom=branch). The later is necessary
because spotless needs a full checkout, which is typically not done by
default by CI platforms like GitHub Actions.

In Github Actions, `spotlessCheck` is made a separate step in the
"other tests" job.

See reactor/reactor#701

.github/workflows/ci.yml

@@ -42,14 +42,22 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
     - uses: actions/setup-java@v1
       with:
         java-version: 8
     - uses: eskatos/gradle-command-action@v1
-      name: gradle
+      name: license header
       with:
-        arguments: check -x :reactor-core:test --no-daemon
+        arguments: spotlessCheck -PspotlessFrom=origin/${{ github.base_ref }}
         wrapper-cache-enabled: true
         dependencies-cache-enabled: true
         configuration-cache-enabled: true
-#the above should exclude jcstress in master, adding a 3rd job below for jcstress
+    - uses: eskatos/gradle-command-action@v1
+      name: other tests
+      with:
+        arguments: check -x :reactor-core:test --no-daemon
+        wrapper-cache-enabled: true
+        dependencies-cache-enabled: true
+        configuration-cache-enabled: true

build.gradle

@@ -39,6 +39,7 @@ plugins {
 	id 'biz.aQute.bnd.builder' version '5.0.1' apply false
 	id 'io.spring.nohttp' version '0.0.5.RELEASE'
 	id "io.github.reyerizo.gradle.jcstress" version "0.8.11" apply false
+	id "com.diffplug.spotless" version "5.14.0"
 }
 
 apply plugin: "io.reactor.gradle.detect-ci"
@@ -106,6 +107,27 @@ nohttp {
 	allowlistFile = project.file('codequality/nohttp/allowlist.lines')
 }
 
+spotless {
+	if (project.hasProperty("spotlessFrom")) {
+		println "[Spotless] Ratchet from $project.spotlessFrom"
+		ratchetFrom project.spotlessFrom
+	}
+	else if (isCiServer) {
+		println "[Spotless] CI detected without explicit branch, not enforcing check"
+		enforceCheck false
+	}
+	else {
+		String spotlessBranch = "origin/3.3.x"
+		println "[Spotless] Local run detected, ratchet from $spotlessBranch"
+		ratchetFrom spotlessBranch
+	}
+	java {
+		target '**/*.java'
+		targetExclude '**/java8stubs/**/*', '**/java9stubs/**/*'
+		licenseHeaderFile('codequality/spotless/licenseSlashstarStyle.txt')
+	}
+}
+
 configure(subprojects) { p ->
 	apply plugin: 'java'
 	apply plugin: 'jacoco'

codequality/spotless/licenseSlashstarStyle.txt

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2011-$today.year VMware Inc. or its affiliates, All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+