fetchurl: fix hashedMirrors with downloadToTemp

fetchurl supports postFetch, which must not run when fetching from
hashedMirrors, because they provide pre-built derivation outputs.

fetchurl also supports downloadToTemp, which modifies behavior relating
to postFetch.

Before this commit, a call like

    fetchurl {
      url = "...";
      downloadToTemp = true;
      postFetch = ''
        mv "$downloadedFile" "$out"
      '';
    }

would work in normal scenarios, but fail when fetching from
hashedMirrors, due to how internally downloadToTemp was not tied to
postFetch as closely as it should've been. This resulted in an error
like

    builder [...] failed to produce output path

This commit fixes this, making hashedMirror fetching work even for
derivations that have downloadToTemp enabled.

Co-Authored-By: Silvan Mosberger <silvan.mosberger@tweag.io>

0 files changed, 0 insertions, 0 deletions