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.