From c1f99ad5d3fbed011f5be70118611153f8a429d0 Mon Sep 17 00:00:00 2001
From: cpovirk <cpovirk@google.com>
Date: Thu, 3 Sep 2026 14:07:20 -0700
Subject: [PATCH] Rip out `MustBeClosed:CheckArena` flag, and improve check
 docs.

PiperOrigin-RevId: 975915464
---
 .../bugpatterns/MustBeClosedChecker.java      | 30 ++----------
 .../bugpatterns/MustBeClosedCheckerTest.java  | 46 -------------------
 docs/bugpattern/MustBeClosedChecker.md        | 10 ++--
 3 files changed, 11 insertions(+), 75 deletions(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/MustBeClosedChecker.java b/core/src/main/java/com/google/errorprone/bugpatterns/MustBeClosedChecker.java
index 2774e57bf78..aa3ac381157 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/MustBeClosedChecker.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/MustBeClosedChecker.java
@@ -33,7 +33,6 @@
 import static com.google.errorprone.util.AnnotationNames.MUST_BE_CLOSED_ANNOTATION;
 
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.ErrorProneFlags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
 import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
@@ -52,13 +51,8 @@
 import com.sun.source.tree.Tree;
 import com.sun.tools.javac.code.Symbol.MethodSymbol;
 import com.sun.tools.javac.code.Type;
-import javax.inject.Inject;
 
-/**
- * Checks if a constructor or method annotated with {@link
- * com.google.errorprone.annotations.MustBeClosed} is called within the resource variable
- * initializer of a try-with-resources statement.
- */
+/** A {@link BugChecker}; see the associated {@link BugPattern} annotation for details. */
 @BugPattern(
     altNames = "MustBeClosed",
     summary =
@@ -80,24 +74,8 @@ public class MustBeClosedChecker extends AbstractMustBeClosedChecker
   private static final Matcher<ExpressionTree> HARDCODED_MUST_BE_CLOSED_METHODS =
       staticMethod().onClass("java.lang.foreign.Arena").namedAnyOf("ofConfined", "ofShared");
 
-  private final Matcher<ExpressionTree> mustBeClosedMatcher;
-
-  @Inject
-  MustBeClosedChecker(ErrorProneFlags flags) {
-    var checkArena =
-        flags
-            .getBoolean("MustBeClosed:CheckArena")
-            .or(() -> flags.getBoolean("MustBeClosedChecker:CheckArena"))
-            .orElse(true);
-    this.mustBeClosedMatcher =
-        checkArena
-            ? anyOf(HAS_MUST_BE_CLOSED_ANNOTATION, HARDCODED_MUST_BE_CLOSED_METHODS)
-            : HAS_MUST_BE_CLOSED_ANNOTATION::matches;
-  }
-
-  public MustBeClosedChecker() {
-    this(ErrorProneFlags.empty());
-  }
+  private static final Matcher<ExpressionTree> MUST_BE_CLOSED_ANNOTATION_OR_METHOD =
+      anyOf(HAS_MUST_BE_CLOSED_ANNOTATION, HARDCODED_MUST_BE_CLOSED_METHODS);
 
   /**
    * Check that the {@code MustBeClosed} annotation is only used for constructors of AutoCloseables
@@ -109,7 +87,7 @@ public Description matchMethod(MethodTree tree, VisitorState state) {
     state.reportMatch(
         scanEntireMethodFor(
             (t, s) -> {
-              if (!mustBeClosedMatcher.matches(t, s)) {
+              if (!MUST_BE_CLOSED_ANNOTATION_OR_METHOD.matches(t, s)) {
                 return false;
               }
               if (t instanceof MethodInvocationTree && getSymbol(t).isConstructor()) {
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/MustBeClosedCheckerTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/MustBeClosedCheckerTest.java
index a11780c514a..ffe34ee90f4 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/MustBeClosedCheckerTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/MustBeClosedCheckerTest.java
@@ -1227,50 +1227,4 @@ Arena unannotatedReturn() {
             """)
         .doTest();
   }
-
-  @Test
-  public void arenaFlagDisabled() {
-    assume().that(Runtime.version().feature()).isAtLeast(22);
-    compilationHelper
-        .setArgs("-XepOpt:MustBeClosed:CheckArena=false")
-        .addSourceLines(
-            "Test.java",
-            """
-            import java.lang.foreign.Arena;
-
-            class Test {
-              void unclosedOfConfined() {
-                Arena arena = Arena.ofConfined();
-              }
-
-              void unclosedOfShared() {
-                Arena arena = Arena.ofShared();
-              }
-            }
-            """)
-        .doTest();
-  }
-
-  @Test
-  public void arenaFlagDisabled_altCheckerName() {
-    assume().that(Runtime.version().feature()).isAtLeast(22);
-    compilationHelper
-        .setArgs("-XepOpt:MustBeClosedChecker:CheckArena=false")
-        .addSourceLines(
-            "Test.java",
-            """
-            import java.lang.foreign.Arena;
-
-            class Test {
-              void unclosedOfConfined() {
-                Arena arena = Arena.ofConfined();
-              }
-
-              void unclosedOfShared() {
-                Arena arena = Arena.ofShared();
-              }
-            }
-            """)
-        .doTest();
-  }
 }
diff --git a/docs/bugpattern/MustBeClosedChecker.md b/docs/bugpattern/MustBeClosedChecker.md
index 66152cb552b..9d7d5f020f3 100644
--- a/docs/bugpattern/MustBeClosedChecker.md
+++ b/docs/bugpattern/MustBeClosedChecker.md
@@ -1,6 +1,10 @@
-Methods or constructors annotated with `@MustBeClosed` require that the returned
-resource is closed. This is enforced by checking that invocations occur within
-the resource variable initializer of a try-with-resources statement:
+Some methods and constructors require that the returned resource is closed. This
+includes user methods/constructors annotated with `@MustBeClosed` and some
+additional well-known APIs. (Some further well-known APIs are covered by a
+different check, StreamResourceLeak.)
+
+This is enforced by checking that invocations occur within the resource variable
+initializer of a try-with-resources statement:
 
 ```java
 try (AutoCloseable resource = createTheResource()) {