Thanks for the PR!

Is there a particular issue that this is solving - or is this just picking up a random FIXME in the code? I'm not opposed to the changes but if there is an underlying bug this is addressing adding tests for those would be good.

We might also want to expose this method in the SQL layer incore_functions, e.g.path_join('...', '...', '...') similar toos.path.join in Python. This might be useful when constructing paths. That would also make testing this method easier.

This isn’t random cleanup. JoinPath is used for temp files, logs, and test paths. Today it just glues strings, so an absolute RHS givesdir//abs/path and duplicate separators/.//../ leak through (the new test shows it). The change normalizes and lets an absolute RHS win. If you want SQL access too, I can add apath_join(...) builtin in a follow-up.

Thanks for the clarification - adding the SQL function in a follow-up makes sense to me.
Could you just add some more tests then, there are a number of edge cases mentioned in the code that appear to be untested, e.g. some tests I could think of:

• JoinPath("dir/subdir/..", "sibling")
• JoinPath("./dir/./subdir/./..", "./sibling/.")
• JoinPath("dir/..", "../..")
• JoinPath("/usr/local", "../..") (this should return "/" I think?)
• JoinPath("/", "usr/local") (follow-up from the previous one)
• JoinPath("/usr/local", "../../..") (not sure what this should return)
• JoinPath("file:/usr/local", "../bin")
• JoinPath("file:/usr/local", "../bin")
• JoinPath("C:\", "..")
• JoinPath("C:\", "..\..")
• JoinPath("C:", "system32")
• JoinPath("C:\", "system32")
• JoinPath("C:drive_relative_path", "path")
• JoinPath("C:drive_relative_path", "..\path") (I think this needs to beC:path,notC:\path, otherwise the relative property is lost)

Maybe we could also add some special tests for Windows specifically, i.e. when the separator is\.

Sure! I will add more edge test cases

• Design: Added a variadic scalar functionpath_join(path, ...) that uses the currentFileSystem::JoinPath to stitch components, inheriting separator normalization, ./.. folding, absolute RHS override, and URI preservation; returns NULL if any argument is NULL. Registered in the built-in list with VARARGS VARCHAR.
• Tests: Added sqllogictesttest/sql/function/string/path_join.test covering duplicate separator cleanup, parent folding, absolute override, root joins, cross-platform separator replacement, and URI preservation.