RFR: 8356645: Javac should utilize new ZIP file system read-only access mode

[ExE Boss]

On Wed, 4 Jun 2025 12:08:38 GMT, David Beaumont <duke at openjdk.org> wrote:

> This PR seeks to integrate the new ZipFileSystem "accessMode" parameter to open internal ZIP/JAR files as read only, to act as defense in-depth against accidental modification.
> 
> Note that this currently also propagates the (currently undocumented) "zipinfo-time" parameter to several other places where ZIP/JAR files are opened, which is likely to improve performance. This was discussed and is expected to be safe (but it's something to be careful about).
> This will, of course, be thoroughly tested before integration.
> 
> It also unifies several places to use a common helper method to obtain the environment map, adds more comments, and changes a small number of affected tests.
> 
> I'm also happy to update the original bug description to include the timestamp related changes as necessary.

src/jdk.compiler/share/classes/com/sun/tools/javac/file/JavacFileManager.java line 565:

> 563:             this.archivePath = archivePath;
> 564:             // Common parameters for opening ZIP/JAR file systems in Javac.
> 565:             Map<String, ?> env = FSInfo.readOnlyJarFSEnv(multiReleaseValue);

Note that this will now cause `.zip` files to be treated the same as `.jar` files when `multiReleaseValue ≠ null` (previously, this was ignored for `.zip` files)

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PR Review Comment: https://git.openjdk.org/jdk/pull/25639#discussion_r2133046832