Introduce IsRefasterAsVarargs matcher for use by Refaster templates

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

@@ -219,7 +219,6 @@ int after(T value1, T value2) {
    */
   static final class MinOfVarargs<T> {
     @BeforeTemplate
-    @SuppressWarnings("StreamOfArray" /* In practice individual values are provided. */)
     T before(@Repeated T value, Comparator<T> cmp) {
       return Stream.of(Refaster.asVarargs(value)).min(cmp).orElseThrow();
     }
@@ -287,7 +286,6 @@ T after(T value1, T value2, Comparator<T> cmp) {
    */
   static final class MaxOfVarargs<T> {
     @BeforeTemplate
-    @SuppressWarnings("StreamOfArray" /* In practice individual values are provided. */)
     T before(@Repeated T value, Comparator<T> cmp) {
       return Stream.of(Refaster.asVarargs(value)).max(cmp).orElseThrow();
     }

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

@@ -25,6 +25,7 @@
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.Matches;
 import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.NotMatches;
 import com.google.errorprone.refaster.annotation.Placeholder;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Arrays;
@@ -46,6 +47,7 @@
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 import tech.picnic.errorprone.refaster.matchers.IsLambdaExpressionOrMethodReference;
+import tech.picnic.errorprone.refaster.matchers.IsRefasterAsVarargs;
 
 /** Refaster rules related to expressions dealing with {@link Stream}s. */
 @OnlineDocumentation
@@ -100,12 +102,9 @@ Stream<T> after(T object) {
    * Prefer {@link Arrays#stream(Object[])} over {@link Stream#of(Object[])}, as the former is
    * clearer.
    */
-  // XXX: Introduce a `Matcher` that identifies `Refaster.asVarargs(...)` invocations and annotate
-  // the `array` parameter as `@NotMatches(IsRefasterAsVarargs.class)`. Then elsewhere
-  // `@SuppressWarnings("StreamOfArray")` annotations can be dropped.
   static final class StreamOfArray<T> {
     @BeforeTemplate
-    Stream<T> before(T[] array) {
+    Stream<T> before(@NotMatches(IsRefasterAsVarargs.class) T[] array) {
       return Stream.of(array);
     }
 

refaster-support/src/main/java/tech/picnic/errorprone/refaster/matchers/IsRefasterAsVarargs.java

@@ -0,0 +1,23 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.refaster.Refaster;
+import com.sun.source.tree.ExpressionTree;
+
+/** A matcher of {@link Refaster#asVarargs} method invocations. */
+public final class IsRefasterAsVarargs implements Matcher<ExpressionTree> {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> DELEGATE =
+      staticMethod().onClass(Refaster.class.getName()).named("asVarargs");
+
+  /** Instantiates a new {@link IsRefasterAsVarargs} instance. */
+  public IsRefasterAsVarargs() {}
+
+  @Override
+  public boolean matches(ExpressionTree expressionTree, VisitorState state) {
+    return DELEGATE.matches(expressionTree, state);
+  }
+}

refaster-support/src/test/java/tech/picnic/errorprone/refaster/matchers/IsRefasterAsVarargsTest.java

@@ -0,0 +1,55 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.bugpatterns.BugChecker;
+import org.junit.jupiter.api.Test;
+
+final class IsRefasterAsVarargsTest {
+  @Test
+  void matches() {
+    CompilationTestHelper.newInstance(MatcherTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import com.google.errorprone.refaster.Refaster;",
+            "",
+            "class A {",
+            "  int[] negative1() {",
+            "    return new int[4];",
+            "  }",
+            "",
+            "  String[] negative2() {",
+            "    return \"foo\".split(\"o\");",
+            "  }",
+            "",
+            "  String[] negative3() {",
+            "    return asVarArgs(\"bar\");",
+            "  }",
+            "",
+            "  String[] positive1() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Refaster.asVarargs(\"o\");",
+            "  }",
+            "",
+            "  private static String[] asVarArgs(String s) {",
+            "    return s.split(\"a\");",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  /** A {@link BugChecker} that simply delegates to {@link IsRefasterAsVarargs}. */
+  @BugPattern(summary = "Flags expressions matched by `IsRefasterAsVarargs`", severity = ERROR)
+  public static final class MatcherTestChecker extends AbstractMatcherTestChecker {
+    private static final long serialVersionUID = 1L;
+
+    // XXX: This is a false positive reported by Checkstyle. See
+    // https://github.com/checkstyle/checkstyle/issues/10161#issuecomment-1242732120.
+    @SuppressWarnings("RedundantModifier")
+    public MatcherTestChecker() {
+      super(new IsRefasterAsVarargs());
+    }
+  }
+}