wip: use jdk17 to build javadoc

.github/workflows/build.yml

@@ -12,7 +12,10 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: gradle/wrapper-validation-action@v1
-      - run: ./gradlew build javadocJar checkMappings --stacktrace
+      - run: |
+        wget https://maven.fabricmc.net/net/java/jdk/openjdk-17-ea%2B24_linux-x64_bin.tar.gz -O java.tar.gz
+        tar -xf java.tar.gz -C ./java17
+      - run: ./gradlew build javadocJar checkMappings --stacktrace -Porg.gradle.java.installations.paths=./java17
       - name: Build artifacts
         if: ${{ matrix.java == '15-jdk' }}
         continue-on-error: true

build.gradle

@@ -833,6 +833,12 @@ javadoc {
 	group = "javadoc generation"
 	outputs.upToDateWhen { false }
 
+	if (ENV.CI) {
+		javaLauncher = javaToolchains.launcherFor {
+			languageVersion = JavaLanguageVersion.of(17)
+		}
+	}
+
 	def mappingPoetJar = project.provider { zipTree configurations.mappingPoetJar.singleFile }
 
 	failOnError = false