RFR: 8355342: File.getCanonicalPath on Java 24 resolves paths on network drives to UNC format [v5]

[Brian Burkhalter]

On Wed, 15 Oct 2025 23:38:40 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> `File.getCanonicalPath` invokes `GetFinalPathNameByHandle` on the result of `canonicalize0` which causes the drive letter of a mapped drive to be converted to a UNC prefix. If such a substitution is detected, this request proposes to revert the conversion of drive letter to UNC prefix before returning the canonical path.
>
> Brian Burkhalter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - 8355342: Fall back to canonicalize0() result if drive letter converted to a long / UNC prefix
>  - Merge
>  - Merge
>  - 8355342: Corrected a comment
>  - 8355342: Add missing space in constant declaration
>  - 8355342: Fix possible sneaky NullPointerException
>  - 8355342: File.getCanonicalPath on Java 24 resolves paths on network drives to UNC format

Commit ebe88f7 changes `WinNTFileSystem::canonicalize` to fall back to the result of `canonicalize0` if `getFinalPath` converts a drive letter + `:` to a path beginning with `\`.  I have investigated and tested various Windows API functions and there does not appear to be a way to determine to exactly which path prefix a drive letter will be mapped by `GetFinalPathNameByHandleW`. No changes to the test are needed.

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PR Comment: https://git.openjdk.org/jdk/pull/27324#issuecomment-3408658546