Add @Nullable to the bound of Supplier.

RELNOTES=`base`: Marked the bound of the type parameter in `Supplier` as `@Nullable` -- including in `guava-android`. TODO(cpovirk): In the release, consider either reverting this or making sure that we've adopted such annotations thoroughly.
PiperOrigin-RevId: 364918297

android/guava/pom.xml

@@ -30,6 +30,10 @@
       <groupId>com.google.code.findbugs</groupId>
       <artifactId>jsr305</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.checkerframework</groupId>
+      <artifactId>checker-qual</artifactId>
+    </dependency>
     <dependency>
       <groupId>org.checkerframework</groupId>
       <artifactId>checker-compat-qual</artifactId>

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

@@ -16,6 +16,7 @@
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A class that can supply objects of a single type; a pre-Java-8 version of {@link
@@ -45,7 +46,7 @@
  * @since 2.0
  */
 @GwtCompatible
-public interface Supplier<T> {
+public interface Supplier<T extends @Nullable Object> {
   /**
    * Retrieves an instance of the appropriate type. The returned object may or may not be a new
    * instance, depending on the implementation.

android/pom.xml

@@ -15,6 +15,7 @@
     <!-- Override this with -Dtest.include="**/SomeTest.java" on the CLI -->
     <test.include>%regex[.*.class]</test.include>
     <truth.version>1.1</truth.version>
+    <checker-framework.version>3.8.0</checker-framework.version>
     <!--
       Upgrading to 1.19 breaks things: Animal Sniffer reports a problem with the
       use of ClassValue in FuturesGetChecked, even though we've added a
@@ -275,6 +276,18 @@
         <artifactId>jsr305</artifactId>
         <version>3.0.2</version>
       </dependency>
+      <dependency>
+        <groupId>org.checkerframework</groupId>
+        <artifactId>checker-qual</artifactId>
+        <version>${checker-framework.version}</version>
+      </dependency>
+      <dependency>
+        <groupId>org.checkerframework</groupId>
+        <artifactId>checker-qual</artifactId>
+        <version>${checker-framework.version}</version>
+        <classifier>sources</classifier>
+      </dependency>
+      <!-- TODO(cpovirk): Remove checker-compat-qual after we finish migrating to type annotations. -->
       <dependency>
         <groupId>org.checkerframework</groupId>
         <artifactId>checker-compat-qual</artifactId>

guava-gwt/pom.xml

@@ -107,6 +107,11 @@
       <groupId>org.checkerframework</groupId>
       <artifactId>checker-qual</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.checkerframework</groupId>
+      <artifactId>checker-qual</artifactId>
+      <classifier>sources</classifier>
+    </dependency>
   </dependencies>
   <build>
     <plugins>
@@ -129,6 +134,8 @@
             <!-- 2. Don't include the source in the jar (since that would let users depend on it from GWT client code, which is compiled from source). -->
             <exclude>**/ForceGuavaCompilation*</exclude>
             <exclude>**/DummyJavadocClass*</exclude>
+            <!-- (unrelated interruption: Also don't include our fabricated CF GWT module descriptor. -->
+            <exclude>**/Qual.gwt.xml</exclude>
           </excludes>
         </configuration>
       </plugin>
@@ -139,6 +146,8 @@
             <!-- 3. Don't include it in the source jar (since it's really more of a "test" than it is production code). -->
             <exclude>**/ForceGuavaCompilation*</exclude>
             <exclude>**/DummyJavadocClass*</exclude>
+            <!-- (unrelated interruption: Also don't include our fabricated CF GWT module descriptor. I don't think anyone should be using our *sources* jar, anyway, at least not as an input to GWT compilation, but it seems safest to exclude here, just as we do for maven-jar-plugin, to be safe. -->
+            <exclude>**/Qual.gwt.xml</exclude>
           </excludes>
         </configuration>
       </plugin>
@@ -299,6 +308,12 @@
                     <include name="**/InternalFutureFailureAccess.java" />
                   </fileset>
                 </copy>
+                <!-- We fabricate a GWT module to cover the CF annotations. Then we inherit it in ForceGuavaCompilation.gwt.xml. -->
+                <echo file="${project.build.directory}/guava-gwt-sources/org/checkerframework/checker/nullness/qual/Qual.gwt.xml">
+                  &lt;module&gt;&lt;source path="" /&gt;&lt;/module&gt;
+                </echo>
+                <!-- TODO(cpovirk): DO NOT RELEASE in this state: I suspect that downstream users of guava-gwt will see their compilation fail from the "missing" CF annotations (whether because those sources are missing entirely or because they're present but without a module descriptor). -->
+                <!-- In contrast to what we do with our *own* sources (i.e., those from guava, guava-testlib, and guava-tests), we *don't* copy the CF annotations to guava-gwt-sources (and so we don't need to unpack them ourselves at all). If we did, they would end up in our generated jar. And we don't need to, anyway: The GWT plugin picks them up automatically because of the <classifier>source</classifier> dependency above. -->
                 <copy toDir="${project.build.directory}/guava-test-gwt-sources">
                   <fileset dir="${project.build.directory}/guava-test-sources">
                     <contains text="@GwtCompatible"/>

guava-gwt/src/com/google/common/ForceGuavaCompilation.gwt.xml

@@ -13,6 +13,7 @@
   <inherits name="com.google.common.xml.Xml" />
   <inherits name="com.google.thirdparty.publicsuffix.PublicSuffixPatterns" />
   <inherits name="com.google.thirdparty.publicsuffix.PublicSuffixType" />
+  <inherits name="org.checkerframework.checker.nullness.qual.Qual" />
 
   <!-- com.google.common.testing.Testing is located in
        GuavaTests under guava-gwt/test -->

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

@@ -16,6 +16,7 @@
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * Legacy version of {@link java.util.function.Supplier java.util.function.Supplier}. Semantically,
@@ -37,7 +38,7 @@
  */
 @GwtCompatible
 @FunctionalInterface
-public interface Supplier<T> extends java.util.function.Supplier<T> {
+public interface Supplier<T extends @Nullable Object> extends java.util.function.Supplier<T> {
   /**
    * Retrieves an instance of the appropriate type. The returned object may or may not be a new
    * instance, depending on the implementation.

pom.xml

@@ -15,6 +15,7 @@
     <!-- Override this with -Dtest.include="**/SomeTest.java" on the CLI -->
     <test.include>%regex[.*.class]</test.include>
     <truth.version>1.1</truth.version>
+    <checker-framework.version>3.8.0</checker-framework.version>
     <!--
       Upgrading to 1.19 breaks things: Animal Sniffer reports a problem with the
       use of ClassValue in FuturesGetChecked, even though we've added a
@@ -274,7 +275,13 @@
       <dependency>
         <groupId>org.checkerframework</groupId>
         <artifactId>checker-qual</artifactId>
-        <version>3.8.0</version>
+        <version>${checker-framework.version}</version>
+      </dependency>
+      <dependency>
+        <groupId>org.checkerframework</groupId>
+        <artifactId>checker-qual</artifactId>
+        <version>${checker-framework.version}</version>
+        <classifier>sources</classifier>
       </dependency>
       <dependency>
         <groupId>com.google.errorprone</groupId>