Fallbacks for CreateSymbolicLinkW, CreateHardLinkW, GetFinalPathNameByHandleW

- `CreateSymbolicLinkW` is used in `std::fs::soft_link`. Fails on unsupported systems.
- `CreateHardLinkW` is used in `std::fs::hard_link`.
- `GetFinalPathNameByHandleW` is used in `std::fs::canonicalize`. Systems that don't support `GetFinalPathNameByHandleW` also don't support symlinks, so the fallback uses `GetFullPathNameW` instead.

Author: seritools

library/std/src/sys/windows/c.rs

@@ -376,6 +376,28 @@ compat_fn_with_fallback! {
 
         TRUE
     }
+
+    // >= Vista / Server 2008
+    // https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createsymboliclinkw
+    pub fn CreateSymbolicLinkW(
+        lpsymlinkfilename: PCWSTR,
+        lptargetfilename: PCWSTR,
+        dwflags: SYMBOLIC_LINK_FLAGS,
+    ) -> BOOLEAN {
+        SetLastError(ERROR_CALL_NOT_IMPLEMENTED);
+        0
+    }
+
+    // >= 2000
+    // https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createhardlinkw
+    pub fn CreateHardLinkW(
+        lpfilename: PCWSTR,
+        lpexistingfilename: PCWSTR,
+        lpsecurityattributes: *const SECURITY_ATTRIBUTES,
+    ) -> BOOL {
+        SetLastError(ERROR_CALL_NOT_IMPLEMENTED);
+        FALSE
+    }
 }
 
 compat_fn_lazy! {
@@ -396,6 +418,15 @@ compat_fn_lazy! {
         lpfileinformation: *mut ::core::ffi::c_void,
         dwbuffersize: u32,
     ) -> BOOL;
+
+    // >= Vista / Server 2008
+    // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfinalpathnamebyhandlew
+    pub fn GetFinalPathNameByHandleW(
+        hfile: HANDLE,
+        lpszfilepath: PWSTR,
+        cchfilepath: u32,
+        dwflags: GETFINALPATHNAMEBYHANDLE_FLAGS,
+    ) -> u32;
 }
 
 compat_fn_optional! {

library/std/src/sys/windows/fs.rs

@@ -1381,13 +1381,24 @@ fn get_path(f: &File) -> io::Result<PathBuf> {
 }
 
 pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
-    let mut opts = OpenOptions::new();
-    // No read or write permissions are necessary
-    opts.access_mode(0);
-    // This flag is so we can open directories too
-    opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS);
-    let f = File::open(p, &opts)?;
-    get_path(&f)
+    if c::GetFinalPathNameByHandleW::option().is_some() {
+        let mut opts = OpenOptions::new();
+        // No read or write permissions are necessary
+        opts.access_mode(0);
+        // This flag is so we can open directories too
+        opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS);
+        let f = File::open(p, &opts)?;
+        get_path(&f)
+    } else {
+        // systems that don't support GetFinalPathNameByHandleW also don't support symlinks, so we
+        // fall back to using GetFullPathName.
+        let path = maybe_verbatim(p)?;
+        let mut file_part = ptr::null_mut();
+        super::fill_utf16_buf(
+            |buf, sz| unsafe { c::GetFullPathNameW(path.as_ptr(), sz, buf, &mut file_part) },
+            |buf| PathBuf::from(OsString::from_wide(buf)),
+        )
+    }
 }
 
 pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {