From 83936d3e2ed5017714862bef42651a6ce38efffd Mon Sep 17 00:00:00 2001
From: Stephan Schroevers <stephan.schroevers@teampicnic.com>
Date: Tue, 20 Jun 2023 09:21:19 -0700
Subject: [PATCH] Avoid `MemberName` IOOBE on lambda parameters inside
 overriding methods

Fixes #3976

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/google/error-prone/pull/3976 from PicnicSupermarket:sschroevers/MemberName-IOOBE 28a9d48e81fc65a601003582182e39e1b3a17c36
PiperOrigin-RevId: 541947784
---
 .../errorprone/bugpatterns/MemberName.java      |  5 ++++-
 .../errorprone/bugpatterns/MemberNameTest.java  | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/MemberName.java b/core/src/main/java/com/google/errorprone/bugpatterns/MemberName.java
index 15b7bee933f8..5c2f63e7ae0f 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/MemberName.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/MemberName.java
@@ -49,6 +49,7 @@
 import com.google.errorprone.suppliers.Supplier;
 import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.Tree.Kind;
 import com.sun.source.tree.VariableTree;
 import com.sun.tools.javac.code.Symbol;
 import com.sun.tools.javac.code.Symbol.MethodSymbol;
@@ -143,7 +144,9 @@ private static boolean hasTestAnnotation(MethodSymbol symbol) {
   public Description matchVariable(VariableTree tree, VisitorState state) {
     VarSymbol symbol = getSymbol(tree);
     String name = tree.getName().toString();
-    if (symbol.owner instanceof MethodSymbol && symbol.getKind().equals(ElementKind.PARAMETER)) {
+    if (symbol.owner instanceof MethodSymbol
+        && symbol.getKind() == ElementKind.PARAMETER
+        && state.getPath().getParentPath().getLeaf().getKind() != Kind.LAMBDA_EXPRESSION) {
       var methodSymbol = (MethodSymbol) symbol.owner;
       int index = methodSymbol.getParameters().indexOf(symbol);
       var maybeSuper = ASTHelpers.streamSuperMethods(methodSymbol, state.getTypes()).findFirst();
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/MemberNameTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/MemberNameTest.java
index d12764996c07..4a4438ee6031 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/MemberNameTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/MemberNameTest.java
@@ -413,4 +413,21 @@ public void initialismsInVariableNames_magicNamesExempt() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void lambdaExpressionParameterInsideOverridingMethod() {
+    helper
+        .addSourceLines(
+            "Test.java",
+            "import java.util.function.Function;",
+            "class Test {",
+            "  @Override",
+            "  public String toString() {",
+            "    // BUG: Diagnostic contains: fooBar",
+            "    Function<String, String> f = foo_bar -> foo_bar;",
+            "    return f.apply(\"foo\");",
+            "  }",
+            "}")
+        .doTest();
+  }
 }