Build fails on Windows when cxx.h is already present in the targets folder due to cache

[aminya]

On Windows, the build fails when a project is built with a cache and cxx.h is already present. It fails to copy cxx.h.

https://github.com/SunDoge/simdjson-rust/runs/8049220520?check_suite_focus=true#step:6:71

error: failed to run custom build command for `simdjson-rust v0.2.0-alpha (D:\a\simdjson-rust\simdjson-rust)`

Caused by:
  process didn't exit successfully: `D:\a\simdjson-rust\simdjson-rust\target\debug\build\simdjson-rust-d635beff2633e3ed\build-script-build` (exit code: 1)
  --- stderr


  cxxbridge error: Failed to copy `C:\Users\runneradmin\.cargo\registry\src\github.com-1ecc6299db9ec823\cxx-1.0.73\include\cxx.h` -> `D:\a\simdjson-rust\simdjson-rust\target\debug\build\simdjson-rust-457ffe0621787f66\out\cxxbridge\include\rust\cxx.h`

  Caused by:
      The filename, directory name, or volume label syntax is incorrect. (os error 123)

SunDoge/simdjson-rust#16

[dtolnay]

Sigh — apparently std::fs::copy on Windows cannot copy between two different drive letters? What a strange error message from the OS in that case. I don't have access to Windows but I am able to reproduce this issue in GitHub Actions.

I tried adding some logging to look at whether the paths involved exists. The path we are copying from does exist, as expected. The path we are copying to does not exist, as expected. The parent directory of the path to does exist, and is a directory, as expected.

from = "C:\\Users\\runneradmin\\.cargo\\git\\checkouts\\cxx-be839b8f5bc98a2b\\1b1f78a\\include\\cxx.h"
from.exists() = true
to = "D:\\a\\simdjson-rust\\simdjson-rust\\target\\debug\\build\\simdjson-rust-73b1080797fedd25\\out\\cxxbridge\\include\\rust\\cxx.h"
to.exists() = false
parent = "D:\\a\\simdjson-rust\\simdjson-rust\\target\\debug\\build\\simdjson-rust-73b1080797fedd25\\out\\cxxbridge\\include\\rust"
parent.exists() = true
parent.is_dir() = true

cxxbridge error: Failed to copy `C:\Users\runneradmin\.cargo\git\checkouts\cxx-be839b8f5bc98a2b\1b1f78a\include\cxx.h` -> `D:\a\simdjson-rust\simdjson-rust\target\debug\build\simdjson-rust-73b1080797fedd25\out\cxxbridge\include\rust\cxx.h`

Caused by:
    The filename, directory name, or volume label syntax is incorrect. (os error 123)

[dtolnay]

Correction, in the above, the path:
D:\\a\\simdjson-rust\\simdjson-rust\\target\\debug\\build\\simdjson-rust-73b1080797fedd25\\out\\cxxbridge\\include\\rust\\cxx.h
does exist, and is a symlink, where read_link on it reports that it points to:
\\??\\C:\\Users\\runneradmin\\.cargo\\git\\checkouts\\cxx-be839b8f5bc98a2b\\88c2051\\include\\cxx.h
which does not exist, which is why exists() reports false on the link. We are using .exists() incorrectly and should be using something like .symlink_metadata().is_ok().

[dtolnay]

That fix makes it proceed slightly further but it still doesn't work because cxx-build is unable to get rid of the old dangling symlink, despite now knowing that it exists. On Windows std::fs::remove_file(path) returns "Access is denied" error if path is a symlink whose target no longer exists.

[aminya]

Thanks for fixing this!