✨ Add errorprone and fix warnings/errors

The compiler will also treat all warnings as errors from now on.

build.gradle

@@ -15,6 +15,7 @@ plugins {
     id 'java-library'
     id 'com.github.johnrengelman.shadow' version '6.1.0'
     id 'de.marcphilipp.nexus-publish' version '0.4.0'
+    id 'net.ltgt.errorprone' version '1.3.0'
 }
 
 apply from: 'scripts/dependencies.gradle'
@@ -59,6 +60,7 @@ subprojects {
     apply plugin: 'java-library'
     apply plugin: 'signing'
     apply plugin: 'de.marcphilipp.nexus-publish'
+    apply plugin: 'net.ltgt.errorprone'
 
     test {
         useJUnitPlatform()
@@ -69,6 +71,21 @@ subprojects {
         withJavadocJar()
     }
 
+    tasks.withType(JavaCompile).configureEach {
+        options.compilerArgs << "-Xlint:all" << "-Xlint:-processing" << "-Werror"
+        options.errorprone {
+            /* These are just annoying */
+            disable(
+                    "JdkObsolete",
+                    "FutureReturnValueIgnored",
+                    "ImmutableEnumChecker",
+                    "StringSplitter",
+                    "EqualsGetClass",
+                    "CatchAndPrintStackTrace"
+            )
+        }
+    }
+
     repositories {
         mavenLocal()
         mavenCentral()
@@ -115,6 +132,8 @@ subprojects {
         compileOnly "org.checkerframework:checker-qual:${vers['checker-qual']}"
         api "io.leangen.geantyref:geantyref:${vers['geantyref']}"
         testImplementation "org.junit.jupiter:junit-jupiter-engine:${vers['jupiter-engine']}"
+        errorprone "com.google.errorprone:error_prone_core:${vers['errorprone']}"
+        errorproneJavac "com.google.errorprone:javac:9+181-r4173-1"
     }
 
     nexusPublishing {
@@ -180,4 +199,3 @@ subprojects {
     }
 
 }
-