build: stop formatting sources in the Maven build

.vscode/settings.recommended.json

@@ -4,6 +4,8 @@
   // formatOnType and formatOnPaste is a very bad idea for slow formatters
   // (such as an external Google Java Format invocation exec), so just on Save:
   "editor.formatOnSave": true,
+  // Format the changed region, not the whole file, as CONTRIBUTING.md asks.
+  "editor.formatOnSaveMode": "modifications",
   "editor.formatOnType": false,
   "editor.formatOnPaste": false,
 
@@ -21,9 +23,8 @@
       "source.addMissingImports": "never"
     }
   },
-  // Keep this version in sync with the same version in pom.xml
   // NB: Changes to this are only taken into account on start-up, so need to restart.
-  "java.format.settings.google.version": "1.27.0",
+  "java.format.settings.google.version": "2.0.0",
   // TODO https://github.com/eclipse-jdtls/eclipse.jdt.ls/issues/3050
   "java.compile.nullAnalysis.mode": "automatic",
   "java.completion.importOrder": ["#", "", "javax", "java"], //# is static

CONTRIBUTING.md

@@ -37,14 +37,17 @@ information on using pull requests.
 ### Format
 
 Code must be formatted according to the
-[Google Java Style Guide](https://google.github.io/styleguide/javaguide.html).
+[Google Java Style Guide](https://google.github.io/styleguide/javaguide.html),
+using [`google-java-format`](https://github.com/google/google-java-format).
+Format only the lines you change, with an IDE integration or with
+[`google-java-format-diff.py`](https://github.com/google/google-java-format/blob/master/scripts/google-java-format-diff.py):
 
-The Maven build will automagically run
-[`google-java-format`](https://github.com/google/google-java-format) when you
-locally build this project.
+```shell
+git diff -U0 $(git merge-base origin/main HEAD) | google-java-format-diff.py -p1 -i
+```
 
-Pull requests will fail to build if you forget to commit reformatted code, and
-cannot be merged until you fix this.
+Stage new files with `git add` first. In a fork, use the remote that points at
+`google/adk-java` instead of `origin`.
 
 ### Single Commit
 

GEMINI.md

@@ -51,10 +51,10 @@ The project is built using Maven. Use the `./mvnw` wrapper script for all comman
     ./mvnw test
     ```
 
-*   **Format code**:
+*   **Format changed lines**:
 
     ```shell
-    ./mvnw fmt:format
+    git diff -U0 $(git merge-base origin/main HEAD) | google-java-format-diff.py -p1 -i
     ```
 
 *   **Skip tests during build**:
@@ -91,7 +91,8 @@ Once started, the dev UI is available at `http://localhost:8000` (or the specifi
 
 ## Development Conventions
 
-*   **Coding Style**: The project follows the Google Java Style Guide. The `fmt-maven-plugin` is used to format the code automatically.
+*   **Coding Style**: The project follows the Google Java Style Guide. Format
+    changed lines with `google-java-format`.
     *   **Import Style**: Always use import statements instead of fully qualified class names in code. Prefer `import com.google.adk.agents.InvocationContext;` over using `com.google.adk.agents.InvocationContext` directly in the code.
 *   **Testing**: The project uses JUnit 5 for testing. Tests are located in the `src/test/java` directory of each module.
 *   **Contributing**: Contributions are welcome. Please see the `CONTRIBUTING.md` file for more information.

pom.xml

@@ -450,25 +450,6 @@
       </plugins>
     </pluginManagement>
     <plugins>
-      <plugin>
-        <groupId>com.spotify.fmt</groupId>
-        <artifactId>fmt-maven-plugin</artifactId>
-        <version>2.27</version>
-        <dependencies>
-          <dependency>
-            <groupId>com.google.googlejavaformat</groupId>
-            <artifactId>google-java-format</artifactId>
-            <version>1.27.0</version>
-          </dependency>
-        </dependencies>
-        <executions>
-          <execution>
-            <goals>
-              <goal>format</goal>
-            </goals>
-          </execution>
-        </executions>
-      </plugin>
       <plugin>
         <groupId>org.jacoco</groupId>
         <artifactId>jacoco-maven-plugin</artifactId>