realpath is not portable to windows for NODERAWFS

[rchiodo]

Version of emscripten/emsdk:
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.19 (a5f7b1c)
clang version 16.0.0 (https://github.com/llvm/llvm-project 30171e76f0e5ea8037bc4d1450dd3e12af4d9938)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /home/rich/source/emsdk/upstream/bin

Building this c program:

#include <sys/types.h>
#include <dirent.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

int main(int argc, char *argv[])
{
    struct dirent *pDirent;
    DIR *pDir;

    // Ensure correct argument count.

    if (argc != 2)
    {
        printf("Usage: main <dirname>\n");
        return 1;
    }

    // Get the realpath
    char cresolved_path[PATH_MAX];
    char * res = realpath(argv[1], cresolved_path);
    if (res == NULL) {
        char error_buf[300] = {0};
        strcpy(error_buf, strerror(errno));
        printf("Cannot real path the directory '%s' with '%s'\n", argv[1], error_buf);
        return -1;
    }

    return 0;
}

With -s NODERAWFS should generate a portable js/wasm combination.

It works fine on linux.

When I run this outputted wasm using node on windows, I get this:

PS C:\Users\aku91\source\repos\debugpyweb> node ..\realpath_c\main.js C:\Users\aku91\source\repos
Cannot real path the directory 'C:\Users\aku91\source\repos' with 'No such file or directory'

I think the problem lies in the realpath implementation. It doesn't look like it would work on windows.

[sbc100]

This looks like of tricky to fix.. because the realpath implementation in musl assumes UNIX directory separators.

Ideally NODERAWFS would somehow override this behaviour, but since its written in native code its hard to do that. Is this a bug that is effecting you in practice? Could your tool mandate that incoming/provided paths are always in UNIX format, or are could you convert them on input?

[rchiodo]

This is affecting CPython. It prevents the startup of CPython because it uses realpath to find files next to itself.

But, I have a fix for this on top of #17849.

Node works fine if you pass it '/' for directory separators. So part of the fix is to ensure directories are always '/'. This can be done in the input or all of the PATH functions inside of emscripten can be changed to replace '\' with '/'.

But CPython already uses '/' itself. So for CPython to work, just this patch is needed:
realpath.patch.txt

[rchiodo]

I was going to submit a PR with that patch after @kleisauke submits #17849