From f57cb1b7ac02c6be1e72d5a04f65c7080c4f9419 Mon Sep 17 00:00:00 2001
From: ghm <ghm@google.com>
Date: Mon, 22 Dec 2025 16:38:30 -0800
Subject: [PATCH] Consider deconstruction of a record to be usage of its record
 component overrides.

I considered just not flagging record component overrides at all, because I assumed they'd be used by `hashCode()`, but they're not! So this is the narrower fix.

PiperOrigin-RevId: 847923360
---
 .../errorprone/bugpatterns/UnusedMethod.java  | 23 ++++++++++
 .../bugpatterns/UnusedMethodTest.java         | 43 +++++++++++++++++++
 2 files changed, 66 insertions(+)

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 6d506e3b924..a045375b95d 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedMethod.java
@@ -28,10 +28,12 @@
 import static com.google.errorprone.matchers.Matchers.SERIALIZATION_METHODS;
 import static com.google.errorprone.suppliers.Suppliers.typeFromString;
 import static com.google.errorprone.util.ASTHelpers.canBeRemoved;
+import static com.google.errorprone.util.ASTHelpers.getEnclosedElements;
 import static com.google.errorprone.util.ASTHelpers.getSymbol;
 import static com.google.errorprone.util.ASTHelpers.getType;
 import static com.google.errorprone.util.ASTHelpers.hasAnnotation;
 import static com.google.errorprone.util.ASTHelpers.isGeneratedConstructor;
+import static com.google.errorprone.util.ASTHelpers.isRecord;
 import static com.google.errorprone.util.ASTHelpers.isSubtype;
 import static com.google.errorprone.util.MoreAnnotations.asStrings;
 import static com.google.errorprone.util.MoreAnnotations.getAnnotationValue;
@@ -49,10 +51,12 @@
 import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.AssignmentTree;
 import com.sun.source.tree.ClassTree;
 import com.sun.source.tree.CompilationUnitTree;
+import com.sun.source.tree.DeconstructionPatternTree;
 import com.sun.source.tree.IdentifierTree;
 import com.sun.source.tree.MemberReferenceTree;
 import com.sun.source.tree.MemberSelectTree;
@@ -280,6 +284,25 @@ public Void visitAssignment(AssignmentTree tree, Void unused) {
         return super.visitAssignment(tree, null);
       }
 
+      @Override
+      public Void visitDeconstructionPattern(DeconstructionPatternTree tree, Void unused) {
+        var symbol = getSymbol(tree.getDeconstructor());
+        if (isRecord(symbol)) {
+          ImmutableSet<Name> componentNames =
+              getEnclosedElements(symbol).stream()
+                  .filter(ASTHelpers::isRecord)
+                  .map(Symbol::getSimpleName)
+                  .collect(toImmutableSet());
+          for (Symbol e : getEnclosedElements(symbol)) {
+            if (componentNames.contains(e.getSimpleName())) {
+              handle(e);
+            }
+          }
+        }
+
+        return super.visitDeconstructionPattern(tree, null);
+      }
+
       private void handle(Symbol symbol) {
         if (symbol instanceof MethodSymbol) {
           unusedMethods.remove(symbol);
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..813e0e9e358 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/UnusedMethodTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/UnusedMethodTest.java
@@ -695,4 +695,47 @@ public void run() {}
             """)
         .doTest();
   }
+
+  @Test
+  public void overriddenRecordGetter_isUsedByDestructuring() {
+    helper
+        .addSourceLines(
+            "Test.java",
+            """
+            class Test {
+              private record R(int x, int y) {
+                @Override
+                public int x() {
+                  return x;
+                }
+              }
+
+              int f(R r) {
+                return switch (r) {
+                  case R(int x, int y) -> x;
+                  default -> 0;
+                };
+              }
+            }
+            """)
+        .doTest();
+  }
+
+  @Test
+  public void otherOverriddenMethod_stillFlagged() {
+    helper
+        .addSourceLines(
+            "Test.java",
+            """
+            class Test {
+              private record R(int x, int y) {
+                // BUG: Diagnostic contains:
+                public int frobnicator() {
+                  return x;
+                }
+              }
+            }
+            """)
+        .doTest();
+  }
 }