From 457c855f5dfae3fbc09333317cd0b6307f7024d1 Mon Sep 17 00:00:00 2001
From: Petr Portnov <mrjarviscraft@gmail.com>
Date: Thu, 28 Aug 2025 16:22:42 +0300
Subject: [PATCH] fix: support implicit `@MethodSource` for `UnusedMethod`

---
 .../errorprone/bugpatterns/UnusedMethod.java  | 12 ++++---
 .../bugpatterns/UnusedMethodTest.java         | 36 +++++++++++++++++--
 2 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java
index 522579538e2..ccfe6d9dd72 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java
@@ -303,10 +303,14 @@ private void handleMethodSource(MethodTree tree) {
         sym.getRawAttributes().stream()
             .filter(a -> a.type.tsym.getQualifiedName().equals(name))
             .findAny()
-            // get the annotation value array as a set of Names
-            .flatMap(a -> getAnnotationValue(a, "value"))
-            .map(
-                y -> asStrings(y).map(state::getName).map(Name::toString).collect(toImmutableSet()))
+            // get the annotation value array as a set of Names,
+            // normalizing unset value to the empty value
+            .map(a -> getAnnotationValue(a, "value")
+                .map(y -> asStrings(y).map(state::getName).map(Name::toString).collect(toImmutableSet()))
+                .orElse(ImmutableSet.of())
+            )
+            // if no explicit method sources were specified, use method name instead
+            .map(names -> names.isEmpty() ? Set.of(sym.name.toString()) : names)
             // remove all potentially unused methods referenced by the @MethodSource
             .ifPresent(
                 referencedNames ->
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/UnusedMethodTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/UnusedMethodTest.java
index 0608003ab8d..e919e647cc7 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/UnusedMethodTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/UnusedMethodTest.java
@@ -318,7 +318,7 @@ public void methodSource() {
             package org.junit.jupiter.params.provider;
 
             public @interface MethodSource {
-              String[] value();
+              String[] value() default "";
             }
             """)
         .addSourceLines(
@@ -339,6 +339,36 @@ private static Stream<String> parameters() {
         .doTest();
   }
 
+  @Test
+  public void implicitMethodSource() {
+    helper
+        .addSourceLines(
+            "MethodSource.java",
+            """
+            package org.junit.jupiter.params.provider;
+
+            public @interface MethodSource {
+              String[] value() default "";
+            }
+            """)
+        .addSourceLines(
+            "Test.java",
+            """
+            import java.util.stream.Stream;
+            import org.junit.jupiter.params.provider.MethodSource;
+
+            class Test {
+              @MethodSource
+              void test() {}
+
+              private static Stream<String> test() {
+                return Stream.of();
+              }
+            }
+            """)
+        .doTest();
+  }
+
   @Test
   public void qualifiedMethodSource() {
     helper
@@ -348,7 +378,7 @@ public void qualifiedMethodSource() {
             package org.junit.jupiter.params.provider;
 
             public @interface MethodSource {
-              String[] value();
+              String[] value() default "";
             }
             """)
         .addSourceLines(
@@ -378,7 +408,7 @@ public void nestedQualifiedMethodSource() {
             package org.junit.jupiter.params.provider;
 
             public @interface MethodSource {
-              String[] value();
+              String[] value() default "";
             }
             """)
         .addSourceLines(