From 0dbf04a0bfbb3398ca06f20856ef0dcb4ef595ff Mon Sep 17 00:00:00 2001
From: Petr Portnov | PROgrm_JARvis <mrJARVIScraft@gmail.com>
Date: Wed, 18 Mar 2026 10:16:51 -0700
Subject: [PATCH] fix: support implicit `@MethodSource` to `UnusedMethod`

Currently, `UnusedMethod` check does not recognize implicitly referenced JUnit `@MethodSource`, e.g. the ones which are derived from test method name when none are specified explicitly. This PR fixes this issue.

Fixes #5289

Fixes #5210

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/error-prone/pull/5210 from JarvisCraft:junit-implicit-method-source 457c855f5dfae3fbc09333317cd0b6307f7024d1
PiperOrigin-RevId: 885662324
---
 .../errorprone/bugpatterns/UnusedMethod.java  | 16 +++++++--
 .../bugpatterns/UnusedMethodTest.java         | 36 +++++++++++++++++--
 2 files changed, 46 insertions(+), 6 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 f1a4f4636cc..4fa5633984a 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java
@@ -329,10 +329,20 @@ 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"))
+            // get the annotation value array as a set of Names,
+            // normalizing unset value to the empty value
             .map(
-                y -> asStrings(y).map(state::getName).map(Name::toString).collect(toImmutableSet()))
+                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() ? ImmutableSet.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 f90464a32b8..c3c10744629 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(String s) {}
+
+              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(