Introduce JUnitSingleArguments bug checker

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArguments.java

@@ -0,0 +1,50 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags uses of {@link
+ * org.junit.jupiter.params.provider.Arguments#arguments(Object...)} with a single (or no) argument;
+ * in such cases the use of {@link org.junit.jupiter.params.provider.Arguments} is not required as a
+ * {@link java.util.stream.Stream} of objects can be directly provided to a {@link
+ * org.junit.jupiter.params.provider.MethodSource}.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "JUnit arguments wrapping a single object are redundant",
+    link = BUG_PATTERNS_BASE_URL + "JUnitSingleArguments",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class JUnitSingleArguments extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> ARGUMENTS_ARGUMENTS =
+      staticMethod().onClass("org.junit.jupiter.params.provider.Arguments").named("arguments");
+
+  /** Instantiates a new {@link JUnitSingleArguments} instance. */
+  public JUnitSingleArguments() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (ARGUMENTS_ARGUMENTS.matches(tree, state) && tree.getArguments().size() <= 1) {
+      return describeMatch(tree, SourceCode.unwrapMethodInvocation(tree, state));
+    }
+
+    return Description.NO_MATCH;
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/JUnitRules.java

@@ -23,6 +23,7 @@ Arguments before(@Repeated T objects) {
     }
 
     @AfterTemplate
+    @SuppressWarnings("JUnitSingleArguments" /* The bugpattern does not understand Repeated. */)
     @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     Arguments after(@Repeated T objects) {
       return arguments(objects);

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArgumentsTest.java

@@ -0,0 +1,30 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class JUnitSingleArgumentsTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(JUnitSingleArguments.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import static java.util.Objects.requireNonNull;",
+            "import static java.util.function.Function.identity;",
+            "import static org.junit.jupiter.params.provider.Arguments.arguments;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    // BUG: Diagnostic contains:",
+            "    arguments();",
+            "    // BUG: Diagnostic contains:",
+            "    arguments(1);",
+            "    arguments(1,2);",
+            "",
+            "    identity();",
+            "    requireNonNull(null);",
+            "  }",
+            "}")
+        .doTest();
+  }
+}

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/util/MethodMatcherFactoryTest.java

@@ -2,7 +2,6 @@
 
 import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
-import static org.junit.jupiter.params.provider.Arguments.arguments;
 
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.BugPattern;
@@ -17,7 +16,6 @@
 import java.util.stream.Stream;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
-import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 
 final class MethodMatcherFactoryTest {
@@ -29,13 +27,13 @@ final class MethodMatcherFactoryTest {
                   "com.example.A#m2(java.lang.String)",
                   "com.example.sub.B#m3(int,int)"));
 
-  private static Stream<Arguments> createWithMalformedSignaturesTestCases() {
+  private static Stream<ImmutableList<String>> createWithMalformedSignaturesTestCases() {
     /* { signatures } */
     return Stream.of(
-        arguments(ImmutableList.of("foo.bar")),
-        arguments(ImmutableList.of("foo.bar#baz")),
-        arguments(ImmutableList.of("a", "foo.bar#baz()")),
-        arguments(ImmutableList.of("foo.bar#baz()", "a")));
+        ImmutableList.of("foo.bar"),
+        ImmutableList.of("foo.bar#baz"),
+        ImmutableList.of("a", "foo.bar#baz()"),
+        ImmutableList.of("foo.bar#baz()", "a"));
   }
 
   @MethodSource("createWithMalformedSignaturesTestCases")