Allow binding to BINDING_VARIABLEs in GuardedByBinder.

PiperOrigin-RevId: 748301805

Author: graememorgan

core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedByBinder.java

@@ -264,18 +264,14 @@ public GuardedByExpression visitIdentifier(IdentifierTree node, BinderContext co
           Symbol symbol = context.resolver.resolveIdentifier(node);
           checkGuardedBy(symbol != null, "Could not resolve %s", node);
           if (symbol instanceof Symbol.VarSymbol varSymbol) {
-            switch (varSymbol.getKind()) {
-              case LOCAL_VARIABLE, PARAMETER -> {
-                return F.localVariable(varSymbol);
-              }
-              case FIELD -> {
-                if (symbol.name.contentEquals("this")) {
-                  return F.thisliteral();
-                }
-                return F.select(computeBase(context, varSymbol), varSymbol);
-              }
+            return switch (varSymbol.getKind()) {
+              case LOCAL_VARIABLE, PARAMETER, BINDING_VARIABLE -> F.localVariable(varSymbol);
+              case FIELD ->
+                  symbol.name.contentEquals("this")
+                      ? F.thisliteral()
+                      : F.select(computeBase(context, varSymbol), varSymbol);
               default -> throw new IllegalGuardedBy(varSymbol.getKind().toString());
-            }
+            };
           } else if (symbol instanceof Symbol.MethodSymbol methodSymbol) {
             return F.select(computeBase(context, symbol), methodSymbol);
           } else if (symbol instanceof Symbol.ClassSymbol) {

core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/GuardedByCheckerTest.java

@@ -2485,4 +2485,30 @@ public synchronized void test(List<?> xs) {
             """)
         .doTest();
   }
+
+  @Test
+  public void bindingVariable() {
+    compilationHelper
+        .addSourceLines(
+            "I.java",
+            """
+            import com.google.errorprone.annotations.concurrent.GuardedBy;
+
+            interface I {
+              class Impl implements I {
+                @GuardedBy("this")
+                private int number = 42;
+              }
+
+              public static void t(I other) {
+                if (other instanceof Impl otherImpl) {
+                  synchronized (otherImpl) {
+                    int a = otherImpl.number;
+                  }
+                }
+              }
+            }
+            """)
+        .doTest();
+  }
 }