More Java 13 pre-reqs (#767)

The `TypeParameterUnusedInFormals` errorprone check is disabled when compiling on Java 13, to workaround an error-prone bug.

changelog/@unreleased/pr-767.v2.yml

@@ -0,0 +1,6 @@
+type: fix
+fix:
+  description: The `TypeParameterUnusedInFormals` errorprone check is disabled when
+    compiling on Java 13, to workaround an error-prone bug.
+  links:
+  - https://github.com/palantir/gradle-baseline/pull/767

gradle-baseline-java/build.gradle

@@ -15,6 +15,7 @@ dependencies {
     compile 'net.ltgt.gradle:gradle-errorprone-plugin'
     compile 'org.apache.maven.shared:maven-dependency-analyzer'
     compile 'org.github.ngbinh.scalastyle:gradle-scalastyle-plugin_2.11'
+    implementation 'org.eclipse.jgit:org.eclipse.jgit'
 
     testCompile gradleTestKit()
     testCompile 'com.github.stefanbirkner:system-rules'

gradle-baseline-java/src/main/groovy/com/palantir/baseline/plugins/BaselineErrorProne.java

@@ -106,6 +106,12 @@ public void apply(Project project) {
                                 errorProneOptions.check("Finally", CheckSeverity.OFF);
                             }
 
+                            if (jdkVersion.compareTo(JavaVersion.toVersion("13.0.0")) >= 0) {
+                                // Errorprone isn't officially compatible with Java13 either
+                                // https://github.com/google/error-prone/issues/1106
+                                errorProneOptions.check("TypeParameterUnusedInFormals", CheckSeverity.OFF);
+                            }
+
                             if (javaCompile.equals(compileRefaster)) {
                                 // Don't apply refaster to itself...
                                 return;

versions.props

@@ -1,4 +1,4 @@
-com.diffplug.spotless:spotless-plugin-gradle = 3.14.0
+com.diffplug.spotless:spotless-plugin-gradle = 3.24.2
 com.google.auto.service:auto-service = 1.0-rc4
 com.google.errorprone:error_prone_annotations = 2.3.3
 com.google.errorprone:error_prone_core = 2.3.3
@@ -12,6 +12,7 @@ org.apache.maven.shared:maven-dependency-analyzer = 1.11.1
 org.github.ngbinh.scalastyle:gradle-scalastyle-plugin_2.11 = 1.0.1
 org.inferred:freebuilder = 1.14.6
 org.slf4j:slf4j-api = 1.7.25
+org.eclipse.jgit:org.eclipse.jgit = 5.3.2.201906051522-r
 
 # test deps
 com.netflix.nebula:nebula-test = 7.2.5