From b337c3273feb6a72d9a64b441e044be183b43d21 Mon Sep 17 00:00:00 2001
From: waterWang <waterWang@users.noreply.github.com>
Date: Tue, 11 Aug 2026 10:16:44 +0800
Subject: [PATCH] fix(UnusedVariable): skip synthetic fields with no explicit
 source position

When Lombok generates a field (e.g., the 'log' field from @Slf4j),
the AST node has a synthetic source position (Position.NOPOS).
The UnusedVariable checker would flag these fields as unused and
attempt to build a fix, but replaceIncludingComments throws a
SourcePositionException because the position doesn't map to any
actual source code.

Fix: add a hasExplicitSource check in handleVariable to skip
variables that don't have a valid source position. This is the
same pattern already used in buildUnusedParameterFixes (line 610)
to handle enum constructors with bogus positions.

Fixes google/error-prone#5964
---
 .../com/google/errorprone/bugpatterns/UnusedVariable.java    | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java
index dca3245af04..43f0421e2aa 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java
@@ -704,6 +704,11 @@ && exemptedFieldBySuperType(getType(variableTree), state)) {
       if (wellKnownKeep.shouldKeep(variableTree)) {
         return;
       }
+      // Skip variables that don't have an explicit source position
+      // (e.g., Lombok-generated fields like @Slf4j's log field).
+      if (!hasExplicitSource(variableTree, state)) {
+        return;
+      }
       switch (symbol.getKind()) {
         case FIELD -> {
           // We are only interested in private fields and those which are not special.