libfetchers/tarball: Lock on effectiveUrl

Basically, if a tarball URL is used as a flake input, and the URL leads
to a redirect, the final redirect destination would be recorded as the
locked URL.

This allows tarballs under https://nixos.org/channels to be used as
flake inputs. If we, as before, lock on to the original URL it would
break every time the channel updates.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index a72cfafa4..c6b219c02 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -145,7 +145,13 @@ DownloadFileResult downloadFile(
     bool immutable,
     const Headers & headers = {});
 
-std::pair<Tree, time_t> downloadTarball(
+struct DownloadTarballMeta
+{
+    time_t lastModified;
+    std::string effectiveUrl;
+};
+
+std::pair<Tree, DownloadTarballMeta> downloadTarball(
     ref<Store> store,
     const std::string & url,
     const std::string & name,