For anyone who wants to verify that these changes are legit, do the following:

1. Check out commit cb6643f (the commit before the formatting change)

2. Add the following to the root pom.xml:

   Spotless plugin

   <!-- Spotless plugin: keeps the code formatted following the google-java-styleguide -->
   <plugin>
     <groupId>com.diffplug.spotless</groupId>
     <artifactId>spotless-maven-plugin</artifactId>
     <version>2.40.0</version>
     <executions>
       <execution>
         <goals>
           <goal>check</goal>
         </goals>
       </execution>
     </executions>
     <configuration>
       <formats>
         <format>
           <includes>
             <include>*.md</include>
             <include>.gitignore</include>
           </includes>
           <trimTrailingWhitespace/>
           <endWithNewline/>
           <indent>
             <spaces>true</spaces>
             <spacesPerTab>4</spacesPerTab>
           </indent>
         </format>
       </formats>
       <java>
         <googleJavaFormat>
           <style>GOOGLE</style>
           <reflowLongStrings>true</reflowLongStrings>
           <formatJavadoc>true</formatJavadoc>
         </googleJavaFormat>
         <importOrder />
         <removeUnusedImports />
         <formatAnnotations />     <!-- Puts type annotations immediately before types. -->.
       </java>
     </configuration>
   </plugin>

3. Run mvn spotless:apply

You should obtain a state nearly identical to what this PR includes. The only changes are in 26 files were comments were modified (I assume because the Spotless plugin / Google Formatter did not properly wrap them).

@MaicolAntali, just for clarification, you edited those comments, right?

FWIW the check I used was to import this change into Google's build system, which does not include timestamps in jar files. Then compile before and after with -g:none (since some line numbers changed) and verify that the resultant Gson jar file is identical.

The only changes are in 26 files were comments were modified (I assume because the Spotless plugin / Google Formatter did not properly wrap them).

Exactly,

What I have done:

• Put comments on new line
• Fix some long single line (//) comments

Original:

// Lorem Ipsum is simply dummy text of the printing and typesetting industry. 
// Lorem Ipsum has been the industry's standard dummy text ever since the 1500s,
// when an unknown printer took a galley of type and scrambled it to make a type specimen book. 

Edited by spotless:

// Lorem Ipsum is simply dummy text of the printing and 
// typesetting industry. 
// Lorem Ipsum has been the industry's standard dummy text ever since the 
// 1500s,
// when an unknown printer took a galley of type and scrambled it to make a type specimen book. 

Committed:

// Lorem Ipsum is simply dummy text of the printing and 
// typesetting industry. Lorem Ipsum has been the industry's 
// standard dummy text ever since the 1500s, when an 
// unknown printer took a ...

Thanks for the confirmation from you both and thanks @MaicolAntali for your dedication with this by manually improving the comment formatting!

FWIW the check I used was to import this change into Google's build system, which does not include timestamps in jar files. Then compile before and after with -g:none (since some line numbers changed) and verify that the resultant Gson jar file is identical.

Thanks for the hint. It looks like locally you can achieve this using the following Maven command:

mvn clean verify jar:test-jar javadoc:jar "-Dproguard.skip" -DskipTests "-Dmaven.compiler.debug=true" "-Dmaven.compiler.debuglevel=none" "-Dproject.build.outputTimestamp=2023-01-01T00:00:00Z"

I only tried this on the changes I obtained locally by running mvn spotless:apply (which as mentioned above slightly differ from the changes of this PR); but unless I messed up my test setup, to me it also looks like the main and test JARs were identical before and after the formatting.