FileStore.getBlockSize() should return the configuration block size

[ogregoire]

The following test case fails for some reason.

  @Test
  void test() throws IOException {
    var blockSize = 1 << 12;
    var configuration = Configuration.unix().toBuilder().setBlockSize(blockSize).build();
    var fs = Jimfs.newFileSystem(configuration);
    var path = fs.getPath("/home/test/test.txt");
    var store = Files.getFileStore(path);
    assertThat(store.getBlockSize()).isEqualTo(blockSize);
  }

I'm explicitly setting the block size, but I get an IOException when the test case is run:

java.lang.UnsupportedOperationException
        at java.base/java.nio.file.FileStore.getBlockSize(FileStore.java:158)
        ...

I would expect the store to return the block size instead.

[ogregoire]

I noticed that the method is new since Java 10. So I guess that a multi-release JAR must be created.

I worked a bit on it and found that it's possible to create such multi-release jar with the following changes:

• Copy JimfsFileStore.java to jimfs/src/main/java10/com/google/common/jimfs/.
• Add the following method at the end of the class:

  @Override
  public long getBlockSize() throws IOException {
    return disk.blockSize();
  }

• Add the following configuration to jimfs/pom.xml:

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <executions>
          <execution>
            <id>compile-java-7</id>
            <goals>
              <goal>compile</goal>
            </goals>
            <configuration>
              <source>1.7</source>
              <target>1.7</target>
            </configuration>
          </execution>
          <execution>
            <id>compile-java-10</id>
            <phase>compile</phase>
            <goals>
              <goal>compile</goal>
            </goals>
            <configuration>
              <release>10</release>
              <compileSourceRoots>
                <compileSourceRoot>${project.basedir}/src/main/java10</compileSourceRoot>
              </compileSourceRoots>
              <multiReleaseOutput>true</multiReleaseOutput>
            </configuration>
          </execution>
        </executions>
      </plugin>
  
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>3.2.0</version>
        <configuration>
          <archive>
            <manifestEntries>
              <Multi-Release>true</Multi-Release>
            </manifestEntries>
          </archive>
        </configuration>
      </plugin>

My only issue was with the tests, hence why I didn't provide a full-blown PR: I don't know how to make tests for a Multi-release project.