RFR: 8268611: jar --validate should check targeted classes in MR-JAR files

[Christian Stein]

On Thu, 14 Nov 2024 11:57:52 GMT, Christian Stein <cstein at openjdk.org> wrote:

> Please review this change ensuring all targeted classes in a MR-JAR file should target the same or a lower classfile version. The [JAR File Specification](https://docs.oracle.com/javase/9/docs/specs/jar/jar.html#Multi-release) of JavaSE 9 reads:
> 
>> A class file under a versioned directory, of version N say, in a multi-release JAR must have a class file version less than or equal to the class file version associated with Nth major version of a Java platform release.
> 
> For example, having compiled source files with `javac` 25 without using the `--release` option (or with `--release 25`) and trying to archive them via a `jar --create --file a.jar --release 9 ... --release 10 ...` command now fails with:
> 
> classfile release value of META-INF/versions/9/version/Version.class too high: 25
> classfile release value of META-INF/versions/10/version/Version.class too high: 25
> invalid multi-release jar file a.jar deleted
> 
> 
> This pull request contains fixes to existing tests which produced invalid MR-JAR files. Most of those fixes are achieved by adding an appropriate `--release N` option to the associated `javac` call. One of those fixes rewrites the classfile version bytes between the `javac` and `jar` calls.

I'll update the message to read:
`META-INF/versions/9/com/foo/Bar.class has class file version 69 (Java 25), but class file version 53 or less is required to target release 9 of the Java Platform`

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PR Comment: https://git.openjdk.org/jdk/pull/22103#issuecomment-2541702479