https://issues.dlang.org/show_bug.cgi?id=17888

          Issue ID: 17888
           Summary: dmd fails on Windows if path is too long
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: laeeth@laeeth.com

DMD fails on Windows if the path is too long.  (Sorry for not giving specific test case yet - I'm on Linux right now, but Atila Neves will elaborate shortly).

This is particularly a problem when using dub, which likes to turn all paths into relative ones and this has the consequence of making even a shortish path long.

There are two reasons for this.  One is that the static array in tk/filespec.c in the function that builds a path is only 131 chars + null.  Another is that for the getcwd Windows API function we call, the MAXPATH limit of 260 characters applies.  The way to avoid this is to use the unicode function and Win32 File namespaces instead of a regular path.  So if the path does not begin \\ then we should make it look something like: \?\C\D\foo  (note, not \?C\D\foo - which does something entirely different).  I believe that should:

1. be one step towards permitting unicode characters in the path.  (probably there are  other functions that would need to be changed - I haven't had time to look).  See  https://issues.dlang.org/show_bug.cgi?id=13493

2. be one step towards removing the path length limit on Windows which interacts badly with dub's style in relativisation of paths.  there might be other functions that need to be changed - in a hurry.

https://github.com/dlang/dmd/blob/2bf9a9d731e88ebd8a175bd0a990a3b651e8df82/src/ddmd/tk/filespec.c line 119 - cwd is 131 chars + null

prototype:
extern (C) char* getcwd(char* buffer, size_t maxlen);

it's deprecated and replaced by the ISO function: https://docs.microsoft.com/en-gb/cpp/c-runtime-library/reference/getcwd-wgetcwd

on Windows and indeed other operating systems we already have the correct code to get current working directory. so we just need to update dmd to use this. https://github.com/dlang/phobos/blob/v2.076.0/std/file.d#L2681

even if we can't use Phobos I guess we could copy /paste that code.

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