From 29bdf78481a86583cd0e1990e8c7eef3ece19aa7 Mon Sep 17 00:00:00 2001
From: Vincent Koeman <vincent.koeman@teampicnic.com>
Date: Fri, 6 Oct 2023 17:07:51 +0200
Subject: [PATCH] Introduce `JUnitSingleArguments` bug checker

---
 .../bugpatterns/JUnitSingleArguments.java     | 50 +++++++++++++++++++
 .../bugpatterns/JUnitSingleArgumentsTest.java | 26 ++++++++++
 2 files changed, 76 insertions(+)
 create mode 100644 error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArguments.java
 create mode 100644 error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArgumentsTest.java

diff --git a/error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArguments.java b/error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArguments.java
new file mode 100644
index 0000000000..9100456858
--- /dev/null
+++ b/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;
+  }
+}
diff --git a/error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArgumentsTest.java b/error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArgumentsTest.java
new file mode 100644
index 0000000000..544b16a918
--- /dev/null
+++ b/error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/JUnitSingleArgumentsTest.java
@@ -0,0 +1,26 @@
+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 org.junit.jupiter.params.provider.Arguments.arguments;",
+            "import java.util.stream.Stream;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    // BUG: Diagnostic contains:",
+            "    arguments();",
+            "    // BUG: Diagnostic contains:",
+            "    arguments(1);",
+            "    arguments(1,2);",
+            "  }",
+            "}")
+        .doTest();
+  }
+}