dune build failed on Windows.

[CanftIn]

Expected Behavior

dune build pass.

Actual Behavior

Reproduction

• PR with a reproducing test:

1. By following the quick-start, make two files: hello-world.ml, dune. Then build a project named hello-world on Windows. There's a error occurred:

$ dune build hello_world.exe
Error: exception
Sys_error("C:/cygwin/home/appveyor/.opam/ocaml-variants.4.09.0+mingw64c/lib/ocaml\\Makefile.config:
No such file or directory")
Raised by primitive operation at file "stdlib.ml", line 398, characters 28-54
Called from file "src/stdune\\io.ml", line 55, characters 17-37
Called from file "src/stdune\\io.ml" (inlined), line 107, characters 25-69
Called from file "src/ocaml-config\\ocaml_config.ml", line 312, characters
  16-37
Called from file "src/ocaml-config\\ocaml_config.ml", line 494, characters
  15-45
Called from file "src/dune\\context.ml", line 405, characters 14-36
Called from file "src/fiber\\fiber.ml", line 196, characters 36-41
Called from file "src/fiber\\fiber.ml", line 102, characters 8-15

I must not crash.  Uncertainty is the mind-killer. Exceptions are the
little-death that brings total obliteration.  I will fully express my cases.
Execution will pass over me and through me.  And when it has gone past, I
will unwind the stack along its path.  Where the cases are handled there will
be nothing.  Only I will remain.

2. dune path:

D:\linux_home\.opam\4.09.0+mingw64c\bin

3. ocaml with cygwin path:

D:\OCaml64

4. Environment variables HOME=D:\linux_home

Specifications

• Version of dune : 2.4.0
• Version of ocaml : 4.09.0
• Operating system : Microsoft Windows [Version 10.0.18363.752]

Additional information

This error seems to be due to dune can not find cygwin path.
And my cygwin is at D:\OCaml64\Cygwin.bat.

[ghost]

Does the above file exist on your system?

C:\cygwin\home\appveyor\.opam\ocaml-variants.4.09.0+mingw64c\lib\ocaml\Makefile.config

[CanftIn]

@diml
This file location on my system is:

D:\linux_home\.opam\4.09.0+mingw64c\lib\ocaml\Makefile.config

Because I set HOME environment variables as D:\linux_home.

And my ocaml install path is :

D:\OCaml64

so dune can not find it.
Is there a way solve this? Thanks.

[ghost]

Is this the system you work on or a CI? I'm asking because of the "appveyor" in the path in the error message.

[CanftIn]

Oh, the truth is I don't have this
C:\cygwin\home\appveyor\.opam\ocaml-variants.4.09.0+mingw64c\lib\ocaml\Makefile.config
on my system cause I don't install cygwin in C drive. I'm not familiar with CI, so I get a little confuse that I have no CI system on the Windows may not matter important.

And dune works fine on my another linux system.

In D:\linux_home\.opam\4.09.0+mingw64c\lib\ocaml\Makefile.config, there is some configs about my local path is

## Arguments passed to the configure script

CONFIGURE_ARGS=--prefix=D:/linux_home/.opam/4.09.0+mingw64c --host=x86_64-w64-mingw32 CC=x86_64-w64-mingw32-gcc CPP=x86_64-w64-mingw32-cpp

## Top build directory

TOP_BUILDDIR = .

## Installation directories

prefix=D:/linux_home/.opam/4.09.0+mingw64c

I just do a stupid way to create the above path by making fold one by one. And copy D:\linux_home\.opam\4.09.0+mingw64c\lib\ocaml\Makefile.config to the created fold.

Then I build dune project. And get another error:

λ dune build hello_world.exe
File "command line", line 1:
Error: Unbound module Stdlib

BTW, maybe I should focus on linux environment rather than Windows.

[bschommer]

Since you did not install cygwin I assume that you have installed a precompiled version of OCaml? In that case you may need to set some environment variables in order for OCaml to find its install path.

[ghost]

Indeed, you need to set at least OCAMLLIB to point to the standard library directory.