Move Java-7-VM warning from MoreObjects to Preconditions.

RELNOTES=Increased the aggressiveness of [Guava 30.1](https://github.com/google/guava/releases/tag/v30.1)'s warning log message for running `guava-android` under a Java 7 VM. (Android VMs are unaffected.) If the warning _itself_ causes you trouble, you can eliminate it by silencing the logger for `com.google.common.base.Preconditions` (which is used _only_ for this warning). This warning prepares for [removing support for Java 7 in 2021](#5269). Please report any problems. We have tried to make the warning as safe as possible, but anytime a common library logs, especially as aggressively as we do in this new release, there is the potential for [`NullPointerException`](https://stackoverflow.com/a/41017717/28465) or even [deadlock](https://stackoverflow.com/a/48009613/28465). (To be clear, Guava will not log under Java 8 or Android, but it will under Java 7.)
PiperOrigin-RevId: 361700569

Author: cpovirk

android/guava/src/com/google/common/base/MoreObjects.java

@@ -15,13 +15,10 @@
 package com.google.common.base;
 
 import static com.google.common.base.Preconditions.checkNotNull;
-import static java.util.logging.Level.WARNING;
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
-import com.google.errorprone.annotations.concurrent.GuardedBy;
 import java.util.Arrays;
-import java.util.logging.Logger;
 import org.checkerframework.checker.nullness.compatqual.NullableDecl;
 
 /**
@@ -144,46 +141,13 @@ public static ToStringHelper toStringHelper(String className) {
    * @since 18.0 (since 2.0 as {@code Objects.ToStringHelper}).
    */
   public static final class ToStringHelper {
-    @GuardedBy("ToStringHelper.class")
-    private static boolean performedJava8CompatibilityCheck;
-
-    private static void java8CompatibilityCheck() {
-      @SuppressWarnings("GuardedBy")
-      boolean racyReadForDoubleCheckedLock = performedJava8CompatibilityCheck;
-      if (racyReadForDoubleCheckedLock) {
-        return;
-      }
-      synchronized (ToStringHelper.class) {
-        if (performedJava8CompatibilityCheck) {
-          return;
-        }
-        performedJava8CompatibilityCheck = true;
-      }
-
-      try {
-        Java8Usage.performCheck();
-      } catch (Throwable underlying) {
-        Exception toLog =
-            new Exception(
-                "Guava will drop support for Java 7 in 2021. Please let us know if this will cause"
-                    + " you problems: https://github.com/google/guava/issues/5269",
-                underlying);
-        Logger.getLogger(ToStringHelper.class.getName())
-            .log(
-                WARNING,
-                "Java 7 compatibility warning: See https://github.com/google/guava/issues/5269",
-                toLog);
-      }
-    }
-
     private final String className;
     private final ValueHolder holderHead = new ValueHolder();
     private ValueHolder holderTail = holderHead;
     private boolean omitNullValues = false;
 
     /** Use {@link MoreObjects#toStringHelper(Object)} to create an instance. */
     private ToStringHelper(String className) {
-      java8CompatibilityCheck();
       this.className = checkNotNull(className);
     }
 

android/guava/src/com/google/common/base/Preconditions.java

@@ -15,9 +15,11 @@
 package com.google.common.base;
 
 import static com.google.common.base.Strings.lenientFormat;
+import static java.util.logging.Level.WARNING;
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import java.util.logging.Logger;
 import org.checkerframework.checker.nullness.compatqual.NonNullDecl;
 import org.checkerframework.checker.nullness.compatqual.NullableDecl;
 
@@ -1488,4 +1490,21 @@ private static String badPositionIndexes(int start, int end, int size) {
     // end < start
     return lenientFormat("end index (%s) must not be less than start index (%s)", end, start);
   }
+
+  static {
+    try {
+      Java8Usage.performCheck();
+    } catch (Throwable underlying) {
+      Exception toLog =
+          new Exception(
+              "Guava will drop support for Java 7 in 2021. Please let us know if this will cause"
+                  + " you problems: https://github.com/google/guava/issues/5269",
+              underlying);
+      Logger.getLogger(Preconditions.class.getName())
+          .log(
+              WARNING,
+              "Java 7 compatibility warning: See https://github.com/google/guava/issues/5269",
+              toLog);
+    }
+  }
 }

guava/src/com/google/common/base/MoreObjects.java

@@ -15,13 +15,10 @@
 package com.google.common.base;
 
 import static com.google.common.base.Preconditions.checkNotNull;
-import static java.util.logging.Level.WARNING;
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
-import com.google.errorprone.annotations.concurrent.GuardedBy;
 import java.util.Arrays;
-import java.util.logging.Logger;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
@@ -144,46 +141,13 @@ public static ToStringHelper toStringHelper(String className) {
    * @since 18.0 (since 2.0 as {@code Objects.ToStringHelper}).
    */
   public static final class ToStringHelper {
-    @GuardedBy("ToStringHelper.class")
-    private static boolean performedJava8CompatibilityCheck;
-
-    private static void java8CompatibilityCheck() {
-      @SuppressWarnings("GuardedBy")
-      boolean racyReadForDoubleCheckedLock = performedJava8CompatibilityCheck;
-      if (racyReadForDoubleCheckedLock) {
-        return;
-      }
-      synchronized (ToStringHelper.class) {
-        if (performedJava8CompatibilityCheck) {
-          return;
-        }
-        performedJava8CompatibilityCheck = true;
-      }
-
-      try {
-        Java8Usage.performCheck();
-      } catch (Throwable underlying) {
-        Exception toLog =
-            new Exception(
-                "Guava will drop support for Java 7 in 2021. Please let us know if this will cause"
-                    + " you problems: https://github.com/google/guava/issues/5269",
-                underlying);
-        Logger.getLogger(ToStringHelper.class.getName())
-            .log(
-                WARNING,
-                "Java 7 compatibility warning: See https://github.com/google/guava/issues/5269",
-                toLog);
-      }
-    }
-
     private final String className;
     private final ValueHolder holderHead = new ValueHolder();
     private ValueHolder holderTail = holderHead;
     private boolean omitNullValues = false;
 
     /** Use {@link MoreObjects#toStringHelper(Object)} to create an instance. */
     private ToStringHelper(String className) {
-      java8CompatibilityCheck();
       this.className = checkNotNull(className);
     }
 

guava/src/com/google/common/base/Preconditions.java

@@ -15,9 +15,11 @@
 package com.google.common.base;
 
 import static com.google.common.base.Strings.lenientFormat;
+import static java.util.logging.Level.WARNING;
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import java.util.logging.Logger;
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -1431,4 +1433,21 @@ private static String badPositionIndexes(int start, int end, int size) {
     // end < start
     return lenientFormat("end index (%s) must not be less than start index (%s)", end, start);
   }
+
+  static {
+    try {
+      Java8Usage.performCheck();
+    } catch (Throwable underlying) {
+      Exception toLog =
+          new Exception(
+              "Guava will drop support for Java 7 in 2021. Please let us know if this will cause"
+                  + " you problems: https://github.com/google/guava/issues/5269",
+              underlying);
+      Logger.getLogger(Preconditions.class.getName())
+          .log(
+              WARNING,
+              "Java 7 compatibility warning: See https://github.com/google/guava/issues/5269",
+              toLog);
+    }
+  }
 }