avoid PermissionError on Lustre when copying files (fixes #25354)

lib/spack/llnl/util/filesystem.py

@@ -84,6 +84,74 @@
     "visit_directory_tree",
 ]
 
+if sys.version_info < (3, 7, 4):
+    # monkeypatch shutil.copystat to fix PermissionError when copying read-only
+    # files on Lustre when using Python < 3.7.4
+
+    def copystat(src, dst, follow_symlinks=True):
+        """Copy file metadata
+        Copy the permission bits, last access time, last modification time, and
+        flags from `src` to `dst`. On Linux, copystat() also copies the "extended
+        attributes" where possible. The file contents, owner, and group are
+        unaffected. `src` and `dst` are path names given as strings.
+        If the optional flag `follow_symlinks` is not set, symlinks aren't
+        followed if and only if both `src` and `dst` are symlinks.
+        """
+
+        def _nop(args, ns=None, follow_symlinks=None):
+            pass
+
+        # follow symlinks (aka don't not follow symlinks)
+        follow = follow_symlinks or not (os.path.islink(src) and os.path.islink(dst))
+        if follow:
+            # use the real function if it exists
+            def lookup(name):
+                return getattr(os, name, _nop)
+
+        else:
+            # use the real function only if it exists
+            # *and* it supports follow_symlinks
+            def lookup(name):
+                fn = getattr(os, name, _nop)
+                if sys.version_info >= (3, 3):
+                    if fn in os.supports_follow_symlinks:  # novermin
+                        return fn
+                return _nop
+
+        st = lookup("stat")(src, follow_symlinks=follow)
+        mode = stat.S_IMODE(st.st_mode)
+        lookup("utime")(dst, ns=(st.st_atime_ns, st.st_mtime_ns), follow_symlinks=follow)
+
+        # We must copy extended attributes before the file is (potentially)
+        # chmod()'ed read-only, otherwise setxattr() will error with -EACCES.
+        shutil._copyxattr(src, dst, follow_symlinks=follow)
+
+        try:
+            lookup("chmod")(dst, mode, follow_symlinks=follow)
+        except NotImplementedError:
+            # if we got a NotImplementedError, it's because
+            #   * follow_symlinks=False,
+            #   * lchown() is unavailable, and
+            #   * either
+            #       * fchownat() is unavailable or
+            #       * fchownat() doesn't implement AT_SYMLINK_NOFOLLOW.
+            #         (it returned ENOSUP.)
+            # therefore we're out of options--we simply cannot chown the
+            # symlink.  give up, suppress the error.
+            # (which is what shutil always did in this circumstance.)
+            pass
+        if hasattr(st, "st_flags"):
+            try:
+                lookup("chflags")(dst, st.st_flags, follow_symlinks=follow)
+            except OSError as why:
+                for err in "EOPNOTSUPP", "ENOTSUP":
+                    if hasattr(errno, err) and why.errno == getattr(errno, err):
+                        break
+                else:
+                    raise
+
+    shutil.copystat = copystat
+
 
 def getuid():
     if is_windows: