Add Error Prone

build.gradle

@@ -19,6 +19,7 @@ buildscript {
         classpath "org.beryx:badass-jar:2.0.0"
         classpath 'biz.aQute.bnd:biz.aQute.bnd.gradle:7.0.0'
         classpath "io.codearte.gradle.nexus:gradle-nexus-staging-plugin:0.30.0"
+        classpath "net.ltgt.gradle:gradle-errorprone-plugin:3.1.0"
     }
 }
 
@@ -60,7 +61,20 @@ pluginManager.withPlugin('biz.aQute.bnd.builder') { // if plugin applied, execut
 allprojects {
     apply plugin: 'java'
     apply plugin: 'java-library' // to avoid https://github.com/gradle/gradle/issues/1118
-    apply plugin: "org.beryx.jar" // for compiling module-info on Java 8
+    apply plugin: 'org.beryx.jar' // for compiling module-info on Java 8
+
+    // https://errorprone.info/docs/installation requires Java 11+
+    if (JavaVersion.current().isJava11Compatible()) {
+        apply plugin: "net.ltgt.errorprone"
+
+        dependencies {
+            errorprone("com.google.errorprone:error_prone_core:2.23.0")
+        }
+
+        tasks.withType(JavaCompile).configureEach {
+           options.errorprone.disableAllWarnings = true
+        }
+    }
 
     if (!JavaVersion.current().isJava9Compatible()) {
         sourceCompatibility = 1.5

picocli-examples/src/main/java/picocli/examples/arggroup/RepeatingCompositeOptions.java

@@ -49,6 +49,10 @@ public boolean equals(Object obj) {
                     && Objects.equals(other.file, this.file)
                     && Objects.equals(other.rotate, this.rotate);
         }
+
+        public int hashCode() {
+            return Objects.hash(count, file, rotate);
+        }
     }
 
     public static void main(String[] args) {

src/test/java/picocli/ArgGroupTest.java

@@ -47,6 +47,7 @@
 import static org.junit.Assert.*;
 import static picocli.ArgGroupTest.CommandMethodsWithGroupsAndMixins.InvokedSub.withMixin;
 
+@SuppressWarnings("EqualsHashCode") // https://errorprone.info/bugpattern/EqualsHashCode
 public class ArgGroupTest {
     @Rule
     public final ProvideSystemProperty ansiOFF = new ProvideSystemProperty("picocli.ansi", "false");

src/test/java/picocli/CompletionCandidatesTest.java

@@ -248,7 +248,7 @@ class App {
         assertNull(candidates);
     }
 
-    @SuppressWarnings("unchecked")
+    @SuppressWarnings({"unchecked", "ReturnValueIgnored"}) // iterable.iterator() https://errorprone.info/bugpattern/ReturnValueIgnored
     @Test(expected = UnsupportedOperationException.class)
     public void testNoCompletionCandidatesThrowsUnsupportedOperation() throws Exception {
         Class<Iterable<String>> c = (Class<Iterable<String>>) Class.forName("picocli.CommandLine$NoCompletionCandidates");

src/test/java/picocli/ExecuteLegacyTest.java

@@ -408,8 +408,8 @@ public void run() {
         new CommandLine(new App()).parseWithHandlers(new RunFirst().andExit(23),
                                                     defaultExceptionHandler().andExit(25));
         assertEquals(format("" +
-                "blah%n",
-                "<main command>"), systemErrRule.getLog());
+                "blah%n"
+                ), systemErrRule.getLog());
     }
 
     @SuppressWarnings("deprecation")

src/test/java/picocli/HelpTest.java

@@ -2172,7 +2172,7 @@ public void testTextTable() {
                 "  -v, --verbose               show what you're doing while you are doing it%n" +
                 "  -p                          the quick brown fox jumped over the lazy dog. The%n" +
                 "                                quick brown fox jumped over the lazy dog.%n"
-                ,""), table.toString(new StringBuilder()).toString());
+                ), table.toString(new StringBuilder()).toString());
     }
 
     @SuppressWarnings("deprecation")
@@ -2198,7 +2198,7 @@ public void testTextTableAddsNewRowWhenAnyColumnTooLong() {
                         "* -c, --create, --create2, --create3, --create4, --create5, --create6,%n" +
                         "        --create7, --create8%n" +
                         "                              description%n"
-                ,""), table.toString(new StringBuilder()).toString());
+                ), table.toString(new StringBuilder()).toString());
 
         table = TextTable.forDefaultColumns(Help.Ansi.OFF, UsageMessageSpec.DEFAULT_USAGE_WIDTH);
         table.addRowValues("", "-c", ",",
@@ -2208,7 +2208,7 @@ public void testTextTableAddsNewRowWhenAnyColumnTooLong() {
                         "  -c, --create, --create2, --create3, --create4, --create5, --create6,%n" +
                         "        --createAA7, --create8%n" +
                         "                              description%n"
-                ,""), table.toString(new StringBuilder()).toString());
+                ), table.toString(new StringBuilder()).toString());
     }
 
     @Test
@@ -2249,7 +2249,7 @@ class Cat {
                         "  -v, --show-nonprinting   use ^ and M- notation, except for LDF and TAB%n" +
                         "      --help               display this help and exit%n" +
                         "      --version            output version information and exit%n" +
-                        "Copyright(c) 2017%n", "");
+                        "Copyright(c) 2017%n");
         assertEquals(expected, baos.toString());
     }
 
@@ -2323,7 +2323,7 @@ public void testNetstatUsageFormat() {
                         "                between each display.  Press CTRL+C to stop redisplaying%n" +
                         "                statistics.  If omitted, netstat will print the current%n" +
                         "                configuration information once.%n"
-                , "");
+                );
         assertEquals(expected, CustomLayoutDemo.createNetstatUsageFormat(Help.Ansi.OFF));
     }
 

src/test/java/picocli/TypeConversionTest.java

@@ -192,7 +192,7 @@ public void testTypeConversionSucceedsForValidInput() throws Exception {
                 "-Pattern", "a*b", //
                 "-UUID", "c7d51423-bf9d-45dd-a30d-5b16fafe42e2", //
                 "-Currency", "EUR",
-                "-tz", "Japan/Tokyo",
+                "-tz", "Asia/Tokyo",
                 "-byteOrder", "LITTLE_ENDIAN",
                 "-Class", "java.lang.String",
                 "-NetworkInterface", "127.0.0.0",
@@ -233,7 +233,7 @@ public void testTypeConversionSucceedsForValidInput() throws Exception {
         assertEquals("Pattern", Pattern.compile("a*b").pattern(), bean.aPatternField.pattern());
         assertEquals("UUID", UUID.fromString("c7d51423-bf9d-45dd-a30d-5b16fafe42e2"), bean.anUUIDField);
         assertEquals("Currency", Currency.getInstance("EUR"), bean.aCurrencyField);
-        assertEquals("TimeZone", TimeZone.getTimeZone("Japan/Tokyo"), bean.aTimeZone);
+        assertEquals("TimeZone", TimeZone.getTimeZone("Asia/Tokyo"), bean.aTimeZone);
         assertEquals("ByteOrder", ByteOrder.LITTLE_ENDIAN, bean.aByteOrder);
         assertEquals("Class", String.class, bean.aClass);
         assertEquals("NetworkInterface", NetworkInterface.getByInetAddress(InetAddress.getByName("127.0.0.0")), bean.aNetInterface);