[ck0i]

What and why

On Windows, UTIL_isSameFile() and UTIL_isSameFileStat() compared the two paths with strcmp. Any other spelling of the input passed to -o (different case, a ./ or .\ prefix, an absolute path, dir\..\file, a hard link) got past the check, and FIO_openDstFile() then truncated the input when opening the output. With a 200 byte input, zstd -f a.bin -o A.bin exited 0 and left a.bin as a 13 byte frame of empty content. Fixes #4852.

The Windows branch now opens both paths with FILE_READ_ATTRIBUTES and compares the volume serial number and file index from GetFileInformationByHandle(), the same idea as the st_dev/st_ino check on POSIX. An exact name match still returns early, and a path that cannot be opened counts as a different file. The source vs dictionary check goes through UTIL_isSameFileStat() and picks up the same behavior. playTests.sh gets a -o ./tmp case on all platforms and a -o TMP case on Windows. Both fail with the current dev build under MSVC and pass with this change, and the full playTests.sh passes on Windows with an MSVC x64 build.

Checklist

• I searched open pull requests and issues: this problem is not already being addressed.
• Bug fix: it comes with a reproducer or a test that fails without the fix.
• Performance change: numbers from repeated runs are included, with CPU, compiler, flags and data.
• I stated below whether AI or other automated tools were used.

Tools used

This PR was filed by an automated agent.

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