Fixes path_symlink_trailing_slashes on Windows

This commit:
* adds missing `ERROR_ALREADY_EXISTS => __WASI_EEXIST` mapping
* re-routes Win errors into correct WASI values in `symlink_*`
  fns when target exists and/or contains a trailing slash
* remaps `ERROR_INVALID_NAME => __WASI_ENOENT`

build.rs

@@ -200,7 +200,6 @@ mod wasm_tests {
                         "truncation_rights" => true,
                         "fd_readdir" => true,
                         "path_rename_trailing_slashes" => true,
-                        "path_symlink_trailing_slashes" => true,
                         _ => false,
                     }
                 } else {

src/sys/windows/host_impl.rs

@@ -22,7 +22,7 @@ pub(crate) fn errno_from_win(error: winx::winerror::WinError) -> host::__wasi_er
         ERROR_SHARING_VIOLATION => host::__WASI_EACCES,
         ERROR_PRIVILEGE_NOT_HELD => host::__WASI_ENOTCAPABLE, // TODO is this the correct mapping?
         ERROR_INVALID_HANDLE => host::__WASI_EBADF,
-        ERROR_INVALID_NAME => host::__WASI_EINVAL,
+        ERROR_INVALID_NAME => host::__WASI_ENOENT,
         ERROR_NOT_ENOUGH_MEMORY => host::__WASI_ENOMEM,
         ERROR_OUTOFMEMORY => host::__WASI_ENOMEM,
         ERROR_DIR_NOT_EMPTY => host::__WASI_ENOTEMPTY,
@@ -35,6 +35,7 @@ pub(crate) fn errno_from_win(error: winx::winerror::WinError) -> host::__wasi_er
         ERROR_NOT_A_REPARSE_POINT => host::__WASI_EINVAL,
         ERROR_NEGATIVE_SEEK => host::__WASI_EINVAL,
         ERROR_DIRECTORY => host::__WASI_ENOTDIR,
+        ERROR_ALREADY_EXISTS => host::__WASI_EEXIST,
         _ => host::__WASI_ENOTSUP,
     }
 }

src/sys/windows/hostcalls_impl/fs.rs

@@ -346,6 +346,24 @@ pub(crate) fn path_symlink(old_path: &str, resolved: PathGet) -> Result<()> {
                         // try creating a dir symlink instead
                         symlink_dir(old_path, new_path).map_err(Into::into)
                     }
+                    WinError::ERROR_ACCESS_DENIED => {
+                        // does the target exist?
+                        if new_path.exists() {
+                            Err(Error::EEXIST)
+                        } else {
+                            Err(WinError::ERROR_ACCESS_DENIED.into())
+                        }
+                    }
+                    WinError::ERROR_INVALID_NAME => {
+                        // does the target without trailing slashes exist?
+                        let suffix = resolved.path().trim_end_matches('/');
+                        let out_path = concatenate(resolved.dirfd(), Path::new(suffix))?;
+                        if out_path.exists() {
+                            Err(Error::EEXIST)
+                        } else {
+                            Err(WinError::ERROR_INVALID_NAME.into())
+                        }
+                    }
                     e => Err(e.into()),
                 }
             }

winx/src/winerror.rs

@@ -86,6 +86,8 @@ win_error_expand! {
     ERROR_NEGATIVE_SEEK,
     /// The directory name is invalid.
     ERROR_DIRECTORY,
+    /// Cannot create a file when that file already exists.
+    ERROR_ALREADY_EXISTS,
 }
 
 impl WinError {