#13373: Handle long file paths on Windows -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 8.1 Resolution: | Keywords: Operating System: Windows | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Rufflewind): Turns out, despite what [https://msdn.microsoft.com/en- us/library/windows/desktop/aa365530.aspx MSDN] says, `SetCurrentDirectoryW` does not seem to support long paths through the `\\?\` prefix. I saw an [https://news.ycombinator.com/item?id=13093529 anecdote] that it ''does'' work if one opts-in through the Win10-only feature (through manifest and/or (?) registry tweak), as long as you append a backslash. Since it still did not work with the `\\?\` prefix even after appending a backslash, so I can only assume that `\\?\` is broken for `SetCurrentDirectoryW`, but the registry/manifest tweak likely does work. My guess is that because in the past `SetCurrentDirectoryW` never supported `\\?\` to begin with, when they added the Win10 feature, whoever updated the documentation probably copy-pasted that section throughout and forgot that `\\?\` was ''specifically not enabled'' for `SetCurrentDirectoryW` unlike many other functions, likely because it would make the counterpart `GetCurrentDirectoryW` risky for improperly written programs. TL;DR: It does not seem possible to set the current directory to a long path except through the Win-10 only mechanism. Also, a lot of Windows functions will choke on relative paths if the resulting path becomes too long, so users will have to use exclusively `\\?\`-style absolute paths. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13373#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler